2021

Mesoscale Discussion #0090


The severe weather threat for Tornado Watch 7 continues.


SUMMARY...Tornado threat is increasing over portions of the central Florida Panhandle, within WW 007.


DISCUSSION...Latest surface analysis indicates dewpoints increasing across coastal counties across portions of the Florida Panhandle, as winds veer to a more southerly direction ahead of the line of storms now advancing eastward across Walton County. While convection has remained generally elevated inland up to this point, the increasing boundary-layer moisture suggests that risk for surface-based convection is also increasing.  Therefore, tornado risk is likewise becoming greater with time, particularly across the Bay, Calhoun, Liberty, and Gulf County areas over the next 1-2 hours. Some potential for a strong tornado exists, given favorably veering/increasing flow with height observed by the latest KTLH WSR-88D VWP.

Mesoscale Discussion #0165


Concerning...Severe potential...Tornado Watch likely 


Valid 131952Z - 132145Z


Probability of Watch Issuance...95 percent


SUMMARY...The severe threat will continue to increase through mid/late afternoon. Thunderstorms are expected to develop and move into the discussion area around 22z. Supercells capable of producing strong tornadoes, very large hail and damaging wind gusts are expected and a watch will be issued in the next hour.


DISCUSSION...A thick cirrus shield oriented southwest to northeast across the TX South Plains/Panhandle vicinity has limited stronger surface heating somewhat this afternoon. Nevertheless, low level moisture has continued to increase across the region on strong southeasterly low level flow. Steep midlevel lapse rates of 8.0-8.5 C/km are already in place over the region and are contributing to 1000-1500 J/kg MLCAPE. Regional VWP data continues to show favorable shear for supercell development. While low level hodographs remain somewhat small, elongated profiles above 2-3 km indicate favorable conditions for very large hail amid steep lapse rates, and hail greater than 2 inches in diameter appears likely with the strongest cells. Fast-moving cells and strong low level winds also will support damaging wind gusts. 


A narrow corridor has developed from roughly Floyd County TX to Wheeler County TX where thinner cirrus has allowed for stronger heating. Surface temperatures are around 5-10 degrees warmer in this corridor per West TX Mesonet data compared to points to the west. Weaker inhibition is noted in 19z Mesoanalysis data, along with slightly stronger low level lapse rates. This corridor may become more favorable for longer-tracked supercells and strong tornadoes later this afternoon. Nevertheless, strong low level shear and a moist, unstable environment could support tornadogenesis in any semi-discrete cells through early evening.

Mesoscale Discussion #0167


The severe weather threat for Tornado Watch 19, 20 continues.


SUMMARY...A couple of tornadoes have recently been reported with supercells entering Randall and Swisher Counties. Additional storms continue to show moderate to strong rotation across the TX Panhandle. Strong tornadoes continue to be possible over the next couple of hours.


DISCUSSION...Several storms have now produced funnel clouds and tornadoes between Amarillo and Lubbock. Cells over Randall and Swisher County have recently shown strong rotation and will continue to move into a moderately unstable airmass with increasing low-level shear. As a result, expect that the threat for very large hail and additional tornadoes, some possibly strong, will continue downstream for the next few hours. 


Further to the north, a messier storm mode has developed closer to the surface boundary over Moore and Potter Counties. Nevertheless, occasionally strong rotation has been noted. Low level shear is likely being enhanced along the surface boundary, allowing periodic intensification of low level mesocyclones. Damaging gusts and tornadoes will continue to be possible with this activity, despite the more linear/clustered storm mode. 


Additional storms are developing over Hale and Floyd counties. These storms have been struggling to organize, but also will continue to move into a similar airmass as that further to the north where tornadoes have already occurred. These storms also could intensify and produce significant severe weather over the next couple of hours as they approach the far eastern TX Panhandle.

Mesoscale Discussion #0168


The severe weather threat for Tornado Watch 19 continues.


SUMMARY...Indications are that a significant tornado is ongoing across Randall County.


DISCUSSION...Radar indicates an intense, cyclic supercell ongoing across eastern Randall and western Armstrong Counties in Texas currently.  Velocities are suggestive of a significant tornado.  A less intense supercell (with strong rotation aloft) was also located just south of this storm across Swisher County that also recently had a reported tornado.  The cell resides within an axis of strong shear/instability with a significant tornado parameter of 4.  This suggests continued potential for significant tornadogenesis over the next hour or so in downstream areas..

Mesoscale Discussion #0200


Concerning...Severe potential...Tornado Watch likely 


Valid 171556Z - 171800Z


Probability of Watch Issuance...95 percent


SUMMARY...The environment is becoming increasingly favorable for tornadic supercells and a PDS tornado watch will likely be needed within the next hour or two.


DISCUSSION...Regional radar and satellite imagery continues to show deepening convection within the broad and robust warm-air advection regime across much of MS and AL. Some modest clearing occurred briefly ahead of the leading showers over MS and temperatures across much of central and southern MS are now in the mid 70s. Slightly cooler surface temperatures exist across central/southern AL. Dewpoints exhibit a similar trend, with upper 60s/low 70s across much of central/southern MS and mid to upper 60s across central/southern AL. These thermodynamic conditions have eroded much of the convective inhibition across the region, although forecast soundings do suggests some minimal (i.e. MLCIN of -25 J/kg or more) likely remains in place at the top of the boundary layer. Continued moistening of the low-level profile coupled with slight cooling aloft should result in a removal of all convective inhibition.


In addition to improving thermodynamics, the low-level wind fields continue to increase. Recent VAD profiles from LIX and DGX show 50 kts within the 1-2 km layer. Latest VAD from DGX also sampled 0-3 km storm-relative helicity over 350 m2/s2. These strengthening low-level winds are expected to persist while gradually spreading northward/northeastward into more of northern AL. Deep-layer vertical shear is already in place over the region, with 0-6 km bulk shear currently 50 kt over central MS/AL, increasing to 70 kt over northern MS/AL.


In all, the overall environment is expected to becoming increasingly favorable for discrete supercells capable of all severe hazards, including intense tornadoes. These initial storms are forecast to develop within the 17-19Z time frame. A prolonged threat for tornadoes is anticipated across the region, with conditions remaining favorable well into the evening.

Mesoscale Discussion #0202


The severe weather threat for Tornado Watch 29 continues.


SUMMARY...A strong tornado threat will increase from Wayne county, Mississippi to Marengo and Wilcox counties in Alabama over the next 1-2 hours.


DISCUSSION...Shower activity through the morning has continued to deepen and a strong storm has developed in Jones County, MS. This storm has quickly exhibited low-level rotation which is indicative of the favorable low-level shear profile in this region. SPC mesoanalysis shows an area of 300 to 400 m2/s2 of 0-3km SRH in this region which is a result of southeasterly surface winds in local observations in this area and a 50 knot south-southwesterly low-level jet around 1.5km to 2km sampled by the KMOB and KDGX VWP. The ongoing storm in this region in addition to any subsequent development could pose a significant tornado threat given the aforementioned favorable low-level shear profile and STP values around 2 to 3.

Mesoscale Discussion #0203


Concerning...Severe potential...Tornado Watch likely 


Valid 171715Z - 171845Z


Probability of Watch Issuance...95 percent


SUMMARY...The environment will remain favorable for tornadic supercells throughout the afternoon and into the evening. A new PDS Tornado Watch will be issued before 18Z to cover this threat.


DISCUSSION...Recent radar imagery shows a well-defined pre-frontal convective line from northwest AR into southeast TX. Expectation is for this line to continue gradually eastward throughout the day and into the evening. Forward motion within the line has slowed over the past hour or so but continued the approach of the shortwave and downstream destabilization is expected to result in a reinvigoration of the line this afternoon. 


Currently, KPOE VAD wind profile shows strong low-level flow (50-55 kt at 2 km) beneath deep and robust southwesterly flow aloft. This kinematic profile supports strong deep-layer vertical shear. Low-level shear is also expected to become more favorable over time as the low-level winds strengthen further. Additionally, filtered diurnal heating has also be noted, with recent surface observations showing temperatures have increased in the mid to upper 70s. Mesoanalysis now shows MLCAPE around 1500 J/kg throughout this entire region.


The overall environment will remain favorable for supercells through the afternoon and into the evening. There is potential for both supercells within the convective line as well as ahead of it within the open warm sector. These supercells will be capable of all severe hazards, including intense tornadoes, and a new PDS Tornado Watch will be issued by 18Z.

Mesoscale Discussion #0205


The severe weather threat for Tornado Watch 29 continues.


SUMMARY...A small corridor more favorable for the development of a strong tornado may be evolving across south-central MS.


DISCUSSION...Recent KDGX radar imagery reveals a tornadic supercell over Lincoln County MS. This supercell has developed within an environment characterized by strong instability and low-level shear. The environment immediate downstream of this cell is currently free of storms. The area downstream also recently experienced a subtle break in the clouds, allowing for a bit more heating. The surface observation at JAN recently reported 78/68 and is now showing a due south wind at 15 kt. These factors suggest a small corridor more favorable for the development of a strong tornado may be evolving across south-central MS

Mesoscale Discussion #0209


The severe weather threat for Tornado Watch 29, 33 continues.


SUMMARY...A corridor more favorable for the development of strong tornadoes may be evolving across central AL.


DISCUSSION...Radar imagery from BMX, GWX, and MOB continues to show a cluster of supercells over west-central AL. The downstream air mass is characterized by temperatures in the low/mid 70s and dewpoints in the upper 60s. As noted in the recent BMX sounding, this air mass is less buoyant than farther west (along the central MS/AL border) where this cluster initially developed. However, in contrast to the slightly less favorable thermodynamics, surface winds here are more southeasterly, veering to southerly in the low-levels, and then southwesterly farther aloft. This is resulting in considerable low-level vertical shear. Recent VAD profile from BMX sampled 350+ m2/s2 of 0-1 km storm-relative helicity. Given the already organized character of these storms, potential exists for the development of strong tornadoes if a more discrete nature can be maintained.

Mesoscale Discussion #0210


The severe weather threat for Tornado Watch 32 continues.


SUMMARY...The tornado threat is expected to increase late this afternoon/evening.


DISCUSSION...Most of Mississippi is in a relative lull for convective coverage/intensity with more intense convection to the east with the stronger low-level jet and to the west near the surface trough. Within this area, significant clearing has allowed temperatures to warm into the low 80s with dewpoints in the upper 60s yielding MLCAPE of 1500 to 2000 J/kg per SPC mesoanalysis. This strong surface heating has led to deep boundary layer mixing (as evident on the 18Z JAN RAOB) and as a result, surface flow has veered southwesterly across much of Mississippi which has reduced low-level directional shear significantly. However, despite this veered low-level flow, a widespread and potentially intense tornado threat is still expected late this afternoon/evening as the surface trough approaches. 


Low-level flow in proximity to this surface trough has started to back across southeast Arkansas and Louisiana. Expect this trend to continue as the boundary tightens in response to the ejecting upper trough. Evidence of this ejecting trough and the corresponding increase to the flow field can be seen on the KLCH VWP where 1km flow has strengthened by 20 kts (to near 60 knots) within the last hour. Expect this stronger low-level jet to overspread much of the warm sector by 22-00Z which should elongate low-level hodographs substantially.


Expect multiple supercells to develop along this surface boundary in the next few hours and track northeastward through the late afternoon and into the evening hours. In response to the aforementioned instability and strengthening low-level shear, the 12Z HREF shows widespread 4+ STP across much of Mississippi this afternoon/evening with some areas in excess of 6. This environment will support the potential for intense/long-track tornadoes through the late afternoon and evening hours.

Mesoscale Discussion #0212


The severe weather threat for Tornado Watch 29, 33 continues.


SUMMARY...The risk for tornadoes, a couple of which could become strong and particularly damaging, is expected to continue to increase through mid to late evening as an organizing squall line overspreads the region.  This may also be accompanied by more general strong to severe surface gusts.  A new tornado watch will be needed by 7 PM CDT.


DISCUSSION...Large-scale ascent, aided by lower/mid tropospheric warm advection beneath difluent high-level flow, continues to support discrete thunderstorm development within a relatively broad warm sector.  Areas of the warm sector not substantially impacted by prior convection remain characterized by CAPE of 1000-2000 J/kg, and wind profiles across the region exhibit strong deep-layer shear and sizable, clockwise-curved low-level hodographs.  This environment remains potentially conducive to long-lived supercells with strong low-level mesocyclones posing a risk for tornadoes.


While the onset of diurnal cooling could result in at least some decrease in instability by 00-01Z, favorable large-scale forcing for ascent seems likely to maintain discrete storm development across central Alabama, as a linear convective system continues to evolve upstream, across southeastern Louisiana through southern and eastern Mississippi.  This is occurring ahead of a vigorous short wave trough turning east-northeast of the southern Great Plains.  As this feature progresses into the lower/middle Mississippi Valley through mid/late evening, south-southwesterly 850 mb flow is forecast to strengthen in excess of 50 kt in a corridor along/ahead of the evolving squall line.  


Further enlargement of low-level hodographs will maintain the risk for tornadoes with both the discrete supercells preceding the the squall line and those forming within the squall line. This will include the potential for strong tornadoes. Otherwise, corridors of potentially damaging wind gusts will probably begin to increase as the evolving squall line continues to organize and accelerate northeastward.

Mesoscale Discussion #0255


The severe weather threat for Tornado Watch 50 continues.


SUMMARY...A tornadic supercell over northern Hale County may persist with tornado threat expanding east/northeast for several hours.


DISCUSSION...A long-lived supercell, now tornadic and likely producing a strong tornado, continues to move east/northeast across northern Hale County, and has shown no signs of weakening.


The air mass ahead of this cell is unstable and warming as the warm front continues to lift well northeast of the Birmingham area. Latest VWP out of BMX shows 0-1 SRH of 329 m2/s2 given a motion of 245/38 kt, which supports a strong tornado.


Given warm/moist advection east of the cell, the tornado threat may persist for a couple hours as it moves east/northeast across several counties in Alabama.

Mesoscale Discussion #0261


The severe weather threat for Tornado Watch 50 continues.


SUMMARY...A corridor for a long track intense to potentially violent tornado is expected to maximize through the next hour across central AL.


DISCUSSION...An intense tornadic supercell located over Hale County will likely remain unimpeded as it moves to the east-northeast across central AL during the next 1-2 hours.  The near-storm environment is currently primed across central AL with 0-1 km SRH at 600 m2/s2 per observed storm motion according to the KBMX VAD. Given the very moist/strongly sheared environment, expecting a long-track intense (EF3+) and potentially violent tornado to continue east-northeast and reach the I-65 corridor over the next hour or so.

Mesoscale Discussion #0262


The severe weather threat for Tornado Watch 50 continues.


SUMMARY...Strong to intense tornado potential will rapidly increase coincident with the central AL supercell moving into eastern AL.


DISCUSSION...5pm CDT surface mesoanalysis indicates a low-level moisture axis (featuring upper 60s F dewpoints) extending from southwestern AL to I-65 in central AL immediately ahead of the tornadic supercell.  Farther east over eastern AL, surface dewpoints are in the middle to upper 60s.  Forecast soundings (NAM/RAP) both indicate a slight increase in moisture will occur over the next hour across eastern AL ahead of the supercell.  As a result, it seems that moisture quality will remain relatively similar across eastern AL as it is as of 5pm across the I-65 corridor.


The KMXX VAD is showing similar 500-mb flow as KBMX and KFFC.  Given objective analysis indicating 300-400 m2/s2 0-1 km SRH, it seems plausible the tornado risk will continue relatively uninterrupted over the next 1-2 hours as the storm moves towards the AL/GA border. Some cellular interference from the south in the near term may briefly limit overall tornado potential, but once storm interference from the south ceases/relaxes, additional tornadoes (including a strong to intense tornado) are possible through 7pm CDT over eastern AL.

Mesoscale Discussion #0266


The severe weather threat for Tornado Watch 53 continues.


SUMMARY...The greatest risk for a tornado will probably focus over east-central AL over the next 1-2 hours.  The near-storm environment suggests a strong tornado is possible.


DISCUSSION...Surface observations over east-central AL indicate dewpoints in the 67-68 deg F range with mid 70s temperatures.  The 01z RAP forecast sounding from Maxwell AFB indicates 1500 J/kg MLCAPE with around 350 m2/s2 surface to 0.5 km SRH and is similar to the KMXX VAD data.  Given the moist and strongly sheared wind profile, it seems likely the supercell over Chilton County will persist for several more hours.  Although some risk for large hail could intermittently accompany this storm, it appears a tornado threat will be the primary concern---including the possibility for a strong tornado through 10pm CDT.  


The airmass has been relatively slow to moisten across parts of western GA.  The risk for a tornado beyond the AL/GA into parts of western GA is more uncertain later this evening.

Mesoscale Discussion #0268


The severe weather threat for Tornado Watch 52 continues.


SUMMARY...Tornado potential will maximize near the GA/AL border and eventually spread into the greater Atlanta exurbia through 1230 am EDT.  It is uncertain how far east the higher probabilities for a tornado will eventually develop due to increasingly marginal low-level moisture with east extent.


DISCUSSION...Surface analysis indicates mid 60s deg F dewpoints straddling the GA/AL border in west-central GA to the east of a supercell with a history of producing tornadoes (likely strong) over east-central AL.  The latest RAP/NAM indicate lowest 100 mb mean mixing ratios increasing into the 13-14 g/kg range over the next hour with MLCAPE increasing from 750 J/kg to 1000-1200 J/kg.  The KFFC VAD showed 500 m2/s2 0-1km SRH within the moist/sufficiently unstable airmass. Current thinking is the increasingly rich low-level moisture (dewpoints rising from 64-65 to 66) may enable a greater risk for a tornado over the next hour or so.

Mesoscale Discussion #0289


The severe weather threat for Tornado Watch 60 continues.


SUMMARY...A supercell producing a strong tornado may persist for another hour or so as it moves into northwest Louisiana.


DISCUSSION...A tornadic supercell now over Panola County TX has a history of tornadoes, likely strong, with VROT up to 70 kt noted. Although cycling down has been noted recently, this long-lived supercell remains in a favorable environment for tornadoes, with 0-1 SRH over 200 m2/s2, increasing to nearly 300 m2/s2 on VWP, and within a very moist air mass. The 00Z SHV sounding shows around 2100 J/kg MUCAPE, with a minor capping inversion just above 700 mb.

Mesoscale Discussion #0410


The severe weather threat for Tornado Watch 100 continues.


SUMMARY...A tornado threat will persist through at least 7 PM associated with a trio of discrete supercells, though large hail will remain the primary concern. To the northwest across the Texas Panhandle, developing thunderstorms will pose a wind/hail threat over the next couple of hours.


DISCUSSION...A trio of discrete supercells have become established as they move off the dryline and toward the Red River. Radar and satellite trends suggest the more robust northern supercell is likely taking advantage of enhanced low-level helicity along and just north of a warm frontal boundary that is draped along the Red River. This cell has also exhibited notable right deviant motion, likely the result of a strengthening mesocyclone and propagation along the warm front/instability gradient to the east. This cell should continue on an eastward trajectory over the next 1-2 hours and will primarily pose a large hail threat. However, given ambient surface vorticity along the boundary (and backed easterly flow just north of the boundary), the tornado threat will persist. The neighboring storms to the south/southeast may intensify in the coming hours, especially if they can become rooted along the boundary. Upscale growth into a cluster is still expected later this evening after 00Z as storms continue to move east. 


To the northwest, thunderstorm development along the dryline has been underway with a few stronger updrafts noted. This activity is occurring on the northwestern periphery of richer boundary layer moisture where dewpoint remain in the 50s. Sufficient instability (around 1000 J/kg MLCAPE) along with favorable effective bulk shear (35-45 knots) roughly off the dryline should continue to support semi-discrete storms capable of producing severe hail and wind.

Mesoscale Discussion #0436


The severe weather threat for Severe Thunderstorm Watch 113 continues.


SUMMARY...The greatest near-term severe threat, including the potential for 2-2.5 inch diameter large hail, should be focused with a supercell moving eastward.


DISCUSSION...A robust supercell has developed over part of northwest TX in the past hour or so. This storm has recently turned right, and is moving generally eastward into western north TX. Mid to upper 60s surface dewpoints are in place ahead of this activity per recent surface observations from the West TX Mesonet. The presence of steep mid-level lapse rates, rich low-level moisture, and surface temperatures warming into the 80s are all supporting 2000-3000 J/kg of MUCAPE per latest mesoanalysis estimates. This strong instability coupled with 50-60 kt of effective bulk shear will likely foster continued storm intensity and organization with this ongoing supercell in the short term. Large hail appears likely, and very large hail upwards of 2-2.5+ inches in diameter may also occur given the very favorable thermodynamic environment and the presence of a pronounced TBSS from the KLBB radar. The kinematic environment appears somewhat favorable for a tornado with this supercell, as the near-surface flow is backed to southeasterly. However, the low-level wind profile from KDYX/KFDR is not overly strong, and 0-1 km SRH around 100 m2/s2 will probably support just a brief/isolated tornado threat in the short term. Depending on the continued eastward movement of this supercell, a small eastward extension of Severe Thunderstorm Watch 113 may be needed for a part of western north TX in the next hour or two.


**Note: This MCD preceded the Truscott, Texas EF3

Mesoscale Discussion #0480


The severe weather threat for Tornado Watch 125 continues.


SUMMARY...Supercells with a history of tornadoes will likely persist through early evening where a corridor of greater tornado risk appears likely this evening.


DISCUSSION...Several small supercells along and west of I-55 have produced confirmed tornadoes over the last 90 minutes. KDGX analysis shows several low-level mesocyclones with VROTs of 40-50 kts and a considerable TDS near Yazoo City, MS. SPC mesoanalysis and regional VWPS show strong veering wind profiles with 200-300 m2/s2 ESRH ahead of the ongoing storms to near the warm front across north-central Mississippi. A corridor of greater tornado potential is likely evolving. The potential exists for several additional tornadoes, (possibly significant) to develop and track northeastward to the warm front over the next 1 to 3 hours.

Mesoscale Discussion #0488


The severe weather threat for Tornado Watch 127 continues.


SUMMARY...The tornado threat will remain greatest across north central GA, especially near and east of the Atlanta metro area through 16Z.


DISCUSSION...Latest VWP data show low-level shear has strengthened during the past hour with 0-1 km storm relative helicity around 400 m2/s2. Line of storms with embedded cyclic supercells currently moving through the eastern Atlanta metro area will remain in a favorable environment for occasional low-level mesocyclones and tornadoes as it continues east during the next hour as dewpoints continue to rise through the upper 60s F.

Mesoscale Discussion #0493


The severe weather threat for Tornado Watch 129 continues.


SUMMARY...Greatest short-term threat for tornadoes is expected to remain across northern South Carolina through.


DISCUSSION...A couple of supercells with persistent strong low-level mesocyclones and history of tornadoes have crossed into western South Carolina. These storms are moving east near 30 kt along a stalled boundary. Effective bulk shear around 45 kt remains favorable for supercells. Tendency has been for near surface winds to veer to southwesterly with time which has reduced the size of 0-2 km hodographs in the moist warm sector. This suggests greatest near-term tornado threat will probably remain with storms moving east and interacting with the boundary where augmented low-level shear/vorticity resides.

Mesoscale Discussion #0495


The severe weather threat for Tornado Watch 127 continues.


SUMMARY...Tornado watch 127 is scheduled to expire at 20Z. Overall tornado threat is not as high as earlier today, and greatest short-term threat exists across the eastern third of WW 127. Expected tendency is for the tornado threat to gradually decrease with time, but a few storms could still produce locally strong wind gusts and possibly some hail the remainder of the afternoon. Depending on trends, WW 127 might be replaced by a severe thunderstorm watch within the next hour.


DISCUSSION...Low-level winds have been gradually veering during the afternoon as the primary low-level jet shifts northeast through the Carolinas and into the Middle Atlantic. This has resulted in a reduction in size of 0-1 km hodographs and a decrease in overall tornado threat over most of north Georgia. However, the boundary layer is destabilizing, and widely scattered storms will continue developing within a moderately unstable environment where 30-40 kt effective bulk shear remains sufficient for some storms to develop mid-level updraft rotation. Isolated downbursts and hail should become the main threats with any stronger storms developing beyond 20Z.

Mesoscale Discussion #0505


The severe weather threat for Tornado Watch 133 continues.


SUMMARY...The threat for large to very large hail should become maximized in the next couple of hours. Some of the very large hail could be 2-3+ inches in diameter. The tornado threat may gradually increase early this evening with any storms that remain discrete.


DISCUSSION...Convection has erupted over the past hour or two along a composite cold front/dryline. Numerous instances of 1-1.75 inch hail have been reported with this activity. The airmass downstream of these severe storms remains strongly unstable, with MLCAPE of 2500-4000 J/kg present. There have been some storm mergers and interactions along the surface boundary so far, and if this trends continues it could limit the very large hail threat to some extent. Still, given the presence of very steep mid-level lapse rates (8.6 C/km in the 700-500 mb layer) per the 19Z observed sounding from FWD and enhanced flow at mid/upper levels, any supercell that can turn right and move off the boundary will have the potential to produce 2-3+ inch hail over the next couple of hours. Otherwise, the tornado threat may gradually increase through the early evening with any cell that can remain discrete, even though the low-level flow is not forecast to become overly strong.

Mesoscale Discussion #0536


The severe weather threat for Tornado Watch 149 continues.


SUMMARY...A widespread damaging wind threat will continue with a bowing line of storms moving eastward. Isolated embedded tornadoes also remain possible.


DISCUSSION...A well-organized bow will move quickly eastward late this afternoon from from southeastern LA/southern MS into southern/central AL over the next couple of hours. The most progressive portion of this line is advancing around 40-45 kt into west-central AL as of 2145Z. Other storms have formed along an outflow boundary extending from near Tuscaloosa to just south of Birmingham to near Auburn AL. This outflow boundary will likely serve as the northern limit to any substantial severe threat. Given the current intensity of the bowing complex, the presence of moderate to locally strong instability downstream (MLCAPE generally 2000-2500 J/kg), sufficient deep-layer shear, and steepened low-level lapse rates from diurnal heating, widespread severe/damaging winds of 60-70+ mph will remain the primary severe threat in the short term. Although low-level winds are not very strong ahead of the ongoing severe convection, up to 100 m2/s2 of 0-1 km SRH may still support some potential for embedded low-level circulations and a brief/isolated tornado threat.

Mesoscale Discussion #0651


Concerning...Severe potential...Tornado Watch likely 


Valid 171911Z - 172115Z


Probability of Watch Issuance...95 percent


SUMMARY...Thunderstorm initiation is anticipated with the next hour or two across far southeast NM/far southwestern TX Panhandle/western Permian Basin. Supercells capable of all severe hazards are possible and a Tornado Watch will be issued to cover the severe threat.


DISCUSSION...Recent surface analysis places a low over about 45 miles northwest of ROW. A dryline extends southeastward from this low through much of southeast NM before arcing back more southward across the TX Trans Pecos. Northward returning low-level moisture also results in an effective warm front, which extends from the surface low northeastward through De Baca County NM and then back southeastward through the TX South Plains. Deepen cumulus has been observed within the area between these two boundaries, with a few orphan anvils recently noted. 


Expectation is for eventual convective initiation along the dryline as it continues eastward/northeastward. Air mass across the region has become moderately unstable, with mesoanalysis estimating 1000 to 1500 J/kg of MLCAPE is in place with little to no convective inhibition. Effective deep layer shear is currently around 30 to 40 kt, with a gradual increase anticipated over the next few hours as the shortwave trough moves through. 


Overall environment supports initial supercells capable of all severe hazards, including very large hail (i.e. greater than 2" in diameter) and tornadoes. Some upscale growth is anticipated over time, which will result in a transition to strong wind gusts as the primary severe threat.

Mesoscale Discussion #0653


The severe weather threat for Tornado Watch 183 continues.


SUMMARY...Thunderstorms capable of producing very large hail, locally severe wind gusts, and a couple of tornadoes will be possible into the evening.


DISCUSSION...At 2145Z, strong thunderstorms have developed along an outflow boundary across portions of northwest TX. Relatively strong heating on both sides of the boundary has largely removed MLCINH, so continued intensification and development is expected into the early evening. Moderate-to-strong instability (MLCAPE of 1500-2500 J/kg), effective shear of 35-45 kt, and steep midlevel lapse rates will support very large hail (potentially baseball-size or larger) with the strongest cells. While low-level flow is currently weak, some tornado risk may evolve with any supercell interacting with the boundary, especially as the low-level jet begins to increase toward evening. With generally steep low-level lapse rates across the area, isolated severe wind gusts will also be possible. Some upscale growth is possible this evening in conjunction with the intensifying low-level jet, which would increase the threat of damaging wind with time.

Mesoscale Discussion #0660


The severe weather threat for Tornado Watch 182, 183, 185 continues.


SUMMARY...Threat for very large hail and a few tornadoes continues this evening, with an increasing threat of damaging wind with time.


DISCUSSION...At 0030Z, intense supercells are ongoing across portions of northwest TX, and also southwestward into portions of the TX South Plains. An intense supercell has recently produced a potentially significant tornado across northern Sterling County, based on the strong velocity signature noted on radar. Localized backing of the surface winds is noted near the Sterling County cluster of supercells, which is likely enhancing low-level shear/SRH and aiding in tornado potential, in addition to the ongoing threat of very large hail. MLCAPE of 2000-3000 J/kg, effective shear of 40-50 kt, and very steep midlevel lapse rates (as noted in 00Z DRT sounding) will continue to support intense supercell structures this evening. 


Given the clustering noted in this area, upscale growth is possible within the next 1-2 hours, which would result in an increasing threat of damaging wind gusts with time tonight.

Mesoscale Discussion #0725


The severe weather threat for Severe Thunderstorm Watch 200 continues.


SUMMARY...The potential for a tornado will continue from along the Sheridan/Decatur County line into the Norton/Graham County line. Downstream backing winds and temperature/dewpoint increases are supportive.


DISCUSSION...A tornado has been confirmed near Selden, KS with a supercell that has had relatively persistent 50-60 kt rotational velocity on KGLD 0.5 degree velocity. The environment ahead of the storm is expected to continue to support tornadic potential as winds at Hill City and Norton have backed to east-southeast and strengthened. Temperatures and dewpoints have also risen slightly. A complicating factor could be developing convection in the inflow region of the storm, now evident in Graham County. This could potentially reduce tornado potential quicker than expected.

Mesoscale Discussion #0755


The severe weather threat for Tornado Watch 209, 210 continues.


SUMMARY...Increasing and intensifying thunderstorm development into the 7-9 PM CDT time frame.  This will probably continue to include a few supercells with increasing tornadic potential, along with potential for the evolution of organizing thunderstorm clusters. Areas to the east of the Tornado Watches will continue to monitored for additional severe weather watches.


DISCUSSION...Although isolated to widely scattered thunderstorms are now initiating along the dryline, a much more substantive increase in thunderstorms is underway along a corridor from the Russell, KS vicinity northwestward through the McCook and Scottsbluff areas of western Nebraska.  This appears focused within a broad zone of lower/mid tropospheric warm advection, northeast of somewhat warmer and more strongly capping elevated mixed-layer air (as inferred from 700 mb thermal fields).


Storms near Russell also appear focused near a zone of locally enhanced boundary-layer convergence, near the eastern periphery of a 20-30 kt southerly 850 mb jet, which is forecast to strengthen to 40 kt this evening.  While there may be a tendency for this convection to begin to advect eastward, in the presence of 20-30 kt west-southwesterly ambient deep-layer mean flow, until the low-level jet begins to veer later this evening, strong storm development probably will remain focused near/west-northwest of the Russell vicinity.


Otherwise, a general increase and intensification of thunderstorm activity probably will continue across parts of the Nebraska Panhandle and southwestern into south central Nebraska through 00-02Z, with a tendency for activity to advect east/northeast of the Tornado Watch area.  However, strongest storms, including discrete supercells and upscale growing clusters, probably will remain focused near the edge of the warmer/more strongly capping elevated mixed-layer air, where the more moist and strongly heated boundary-layer is characterized by large CAPE (up to 3000 J/kg).  


As the southerly low-level jet begins to strengthen by early evening, the risk for tornadoes in discrete supercells will probably continue to increase, include potential for a couple of strong tornadoes.

Mesoscale Discussion #0908


Concerning...Severe potential...Tornado Watch likely 


Valid 101956Z - 102130Z


Probability of Watch Issuance...95 percent


SUMMARY...Convective initiation is expected between 20-21 UTC along the dryline over eastern MN near the ND border.  Explosive growth into significant-severe producing supercells is forecast late this afternoon into the early evening.


DISCUSSION...Visible-satellite imagery shows a swelling band of agitated cumulus along the dryline over far eastern MT near Sydney. Temperatures immediately east of the dryline have warmed into the lower 80s with a deepening boundary layer featuring low to mid 60s deg F dewpoints.  The 18 UTC Glasgow, MT raob showed a very steep 700-500 mb lapse rate (8.6 deg C/km).  Modifying the raob for 19 UTC surface conditions east of the dryline near the ND/MT border (i.e., Sydney, MT) yielded 3300 J/kg MLCAPE with very little convective inhibition remaining.  As the cap erodes, expecting explosive updraft growth quickly evolving into a few discrete supercells.  Giant hail (3+ inches in diameter) is possible with the stronger storms as the organize and move northeast into a less deeply mixed and more moisture rich environment near the warm front.  Supercell tornadoes will be possible in vicinity of the warm front, in addition to the hail/severe gust hazard.  Other isolated storms are forecast to eventually develop southward along the dryline into parts of southwest ND and northwest SD.  Large to giant hail will be the primary hazard with these storms before additional thunderstorm development into a severe squall line evolves later this evening.

Mesoscale Discussion #0909


Concerning...Severe potential...Watch likely 


Valid 102051Z - 102245Z


Probability of Watch Issuance...95 percent


SUMMARY...Supercells are expected to develop along the lee trough later this afternoon. Very large hail, severe wind gusts, and a couple tornadoes are possible. With time, initial storms are likely to grow upscale into intense lines/bowing segments capable of significant wind gusts. A WW is likely within the next 2-3 hours.


DISCUSSION...Cumulus clouds have begun to form along the MT/SD/WY border within the lee trough. Higher-based cumulus are also evident farther south in eastern Wyoming as well. Continued boundary-layer heating and mid-level height falls should continue to promote this development and eventual storm initiation later this afternoon. The 19Z UNR sounding showed extreme surface-based buoyancy, though this was only supported by a very shallow layer of low-level moisture. Farther to the east, the 18Z LBF sounding showed a deeper moist layer with similar instability/buoyancy. This richer moisture is apparent on visible satellite where boundary-layer cumulus have develop in central Nebraska/South Dakota.


Current visible satellite trends suggest that storm development is still likely a 2-4 hours away, which has been the general consensus of CAM guidance today. With 30-45 kts of effective shear orthogonal to the lee trough, initial storms will likely be supercellular and capable of very large hail (potentially 3+ inches) and severe wind gusts. Given the lower boundary layer RH towards the west, the tornado threat is not expected to be overly high, but a couple of tornadoes will be possible. If a storm can remain discrete into the evening, richer moisture to the east and a strengthening low-level jet, a brief window of greater tornado potential could develop.


The main concern beyond the initial supercells is expected to be a threat for significant wind gusts along with linear/bowing segments that develop. Guidance has varied in the exact evolution of convection this evening, but one or two of intense squall lines are possible as storms move into central Nebraska/South Dakota.

Mesoscale Discussion #0910


The severe weather threat for Tornado Watch 251 continues.


SUMMARY...All hazards will remain possible for the next 1-2 hours, including across southwest North Dakota. The greatest near-term tornado risk will likely remain across northwest North Dakota where stronger low-level shear is noted.


DISCUSSION...Radar imagery from KGGW and KMBX show discrete to semi-discrete cells continuing to mature along the surface trough/dryline across far eastern Montana. Several severe hail reports have been noted in the past hour with this activity, as well as organized mesocyclones with the stronger, more persistent storms. Additionally, new convection is attempting to develop along the dryline across southwest North Dakota. Although low-level winds are slightly more veered out of the south across this region, effective SRH values near 100-200 m2/s2 will support a tornado risk with any discrete storm that can develop. 


Further north, more easterly flow to the north of a diffuse surface warm front is supporting higher ESRH values up to 400 m2/s2 per recent RAP Mesoanalysis estimates. This favorable shear, coupled with moderate to high instability owing to surface dewpoints in the mid 60s, is supporting STP values between 3-4 within a narrow zone across northwest ND. This region may see the highest tornado potential in the near-term as storms move from eastern MT into this environment. The duration and coverage of the tornado threat remains somewhat uncertain given boundary-parallel mid-level flow and the potential for storm interactions. However, more zonal effective shear vectors across western ND may continue to support discrete modes as storms progress eastward this evening.

Mesoscale Discussion #0916


The severe weather threat for Severe Thunderstorm Watch 254 continues.


SUMMARY...Severe wind, including significant wind gusts, will remain likely as a strong line of storms moves across northwest North Dakota over the next 1-2 hours.


DISCUSSION...A line of storms moving across western ND has a history of producing severe hail and measured winds over 60 mph with a few reports of 70-90 mph gusts. Radar imagery from KGGW and KMBX shows a well organized squall line that is showing signs of a bowing segment and accompanying rear inflow jet on the northern edge. This line will continue to propagate to the north/northeast across northwest ND on the edge of the instability gradient over the next 1-2 hours. 50-70 knot effective bulk shear will help maintain storm organization, and increasing low-level flow (60-70 knots observed in the lowest 1-2 km layer per KBMX VWP observations) in the vicinity of the advancing surface low suggest a high probability of severe, and possibly significant severe, wind gusts as the lines progresses towards the international border.

Mesoscale Discussion #0997


The severe weather threat for Tornado Watch 279 continues.


SUMMARY...A continued tornado threat is expected over west-central OH through 22Z.


DISCUSSION...A supercell has recently become surface-based and become tornadic across extreme east-central IN. The downstream environment across west-central OH will continue to modify late this afternoon as an outflow boundary retreats northeastward, with temperatures warming through the 80s F and MLCINH continuing to erode. A relatively narrow corridor is expected to remain favorable for tornadoes across west-central OH through 22Z, in a region where weakening inhibition will support continued surface-based convection, and relatively strong low-level shear/helicity is in place (per recent KILN VWP) near and to the immediate cool side of the boundary. 


The ongoing tornadic supercell will likely continue to move southeast or east-southeast, with additional supercell development possible from the cluster of storms further to the west across eastern IN. Any sustained supercell with pose a tornado threat, with some risk of a strong tornado near the boundary, given the favorable instability and low-level wind profile. Large hail and locally damaging wind will also be possible.

Mesoscale Discussion #1206


The severe weather threat for Severe Thunderstorm Watch 354 continues.


SUMMARY...Hailstones greater than 2 inches in diameter will be possible with two supercells moving southeastward across western South Dakota over the next couple of hours. Wind driven hail and damaging wind gusts exceeding 70 knots will also be possible.


DISCUSSION...High resolution radar from Rapid City shows a well-developed intense supercell located about 20 statute miles to the east of Rapid City. Another supercell is located in far southwestern North Dakota. The environment ahead of the storms is characterized by moderate instability with MLCAPE near 2000 J/kg, strong deep-layer shear and steep mid-level lapse rates. The 00Z sounding from Rapid City shows 0-6 km near 75 kt with 700-500 mb lapse rate of 8.0 C/km. This will continue to support intense supercell development over the next couple of hours. Hailstones of greater than 2 inches in diameter will be possible within the strongest part of each storm. Wind driven hail and wind gusts exceeding 70 knots will also be possible. These two storms are expected to produce swaths of large hail and wind damage, oriented to the southeast across parts of western South Dakota.

Mesoscale Discussion #1281


Concerning...Severe potential...Watch likely 


Valid 141840Z - 142045Z


Probability of Watch Issuance...95 percent


SUMMARY...Storms are expected to develop by 21Z from the Nebraska/Iowa border across northwest Iowa, with supercell potential spreading east/northeast across Iowa and perhaps extreme southern Minnesota this evening. A few tornadoes will be possible, along with damaging gusts and hail.


DISCUSSION...A diffuse warm front currently extends from northeast NE across central IA, with outflow-cooled air from northeast IA into southwest WI. The outflow farther west across north-central IA has modified somewhat with dewpoints holding near 70 F along with backed surface winds.


Southerly winds are currently gusting to over 20 kt across the MO Valley, with area of heating across western IA and NE. Continued destabilization is therefore likely across these areas, and this is also where surface convergence is focused along the low pressure trough. Farther to the northwest, a secondary from extends from southwest MN into northern NE, and low-topped convection has been noted over far northwest IA.


Lift will continue to consolidate over western IA over the next few hours, where instability and shear parameters will also maximize. A downstream zone of supercell potential will exist in association with the warm front/outflow with enhanced low-level shear and low LCLs. A few tornadoes will be possible, as well as large hail. Damaging wind potential may increase should more of a linear storm mode materialize a few hours after initiation.

Mesoscale Discussion #1286


The severe weather threat for Tornado Watch 378 continues.


SUMMARY...Two supercell thunderstorms in central Iowa have recently had observed tornadoes reported. The mesoscale environment will continue to favor supercells with an attendant tornado threat.


DISCUSSION...A supercell thunderstorm in Calhoun County has recently had a tornado reported with it. A newer storm to the east in Hamilton County has also shown supercell structure with a weak TDS signature on the 0.5 degree KDMX 2109Z scan. These storms are interacting favorably with outflow from a convective complex that moved through the region earlier today. This favorable mesoscale environment will continue to support supercell storms with tornadic potential this afternoon.

Mesoscale Discussion #1288


The severe weather threat for Tornado Watch 378 continues.


SUMMARY...The potential for tornadoes will be focused in northeast Iowa and potential parts of east-central Iowa. Farther west, veered surface flow will limit tornado potential, though damaging winds and perhaps isolated hail remain a possibility.


DISCUSSION...The remaining area of greatest concern for a continued tornado threat exists in northeastern Iowa. A confirmed tornado was located in Bremer County east of Waverly. This storm has remained discrete and will likely be the focus for tornadic potential over the next hour or two. To its southwest, another cluster of supercells has recently grown upscale. While the storm mode would indicate a lower tornado threat, temperatures downstream of these storms have continued to warm into the upper 70s to low 80s F. Surface winds remain backed and will continue to support enhanced low-level SRH and potential for tornadoes.


To the west of I-35, surface winds have veered considerably and are now west to west-southwesterly. Though storms have developed along the cold front, these storms are more of a damaging wind gusts and perhaps isolated large hail threat. The tornado threat in these areas is relatively lower.

Mesoscale Discussion #1378


Concerning...Severe potential...Tornado Watch likely 


Valid 282209Z - 290015Z


Probability of Watch Issuance...95 percent


SUMMARY...Rapid development of supercell thunderstorms is anticipated in the next few hours, with a risk for very large hail, damaging winds, and potentially a few tornadoes.  A Tornado Watch will likely be issued prior to 00z.


DISCUSSION...A warm front extended south/southeast across central/southern MN at 22z, and this front will continue to move east through this evening as a weak surface low moves east across central MN. Latest visible imagery reveals moderate/towering cumulus over central MN north of the Twin Cities area, embedded within a larger area of clouds over central/northern MN and northern WI. Current expectations are for thunderstorms to develop in the next few hours near the warm front and move southeast during the evening. Northwesterly deep-layer shear of 45-55 kts in the vicinity of the front will support intense supercells initially, and locally-enhanced 0-3 km SRH will be favorable for low-level rotation and potential for tornado development. Steep mid-level lapse rates will also support a risk for very large hail, and damaging winds are also expected.  Current thinking is that the tornado threat will warrant a Tornado Watch for the first few hours after initiation given the near-storm environment, with eventual transition into a fast-moving MCS with widespread damaging wind potential later this evening/overnight.  


A Tornado Watch will likely be coordinated with affected NWS Weather Forecast Offices prior to 00z.

Mesoscale Discussion #1391


The severe weather threat for Tornado Watch 401 continues.


SUMMARY...Threat for damaging wind gusts and/or brief tornadoes will continue for the next few hours.


DISCUSSION...A large area of showers and thunderstorms continues to move eastward across the northern Mid-Atlantic. Much of this activity has remained shallow and transient. However, a few more robust updrafts have been able to develop, including two which are currently ongoing over MD, one over Carroll County MD and the other over Howard County MD, and another over Lehigh County PA. Low to mid-level rotation has been noted in each one of these storms, suggesting the slightly stronger flow associated with this shortwave trough (sampled well by recent LWX VAD profiles) coupled with the southerly surface winds is enough to promote updraft rotation. This current trend of transient updrafts capable of damaging wind gusts and/or brief tornadoes will likely continue for the next few hours.


**This MCD preceded the tornadoes in the Philly/Trenton metros

Mesoscale Discussion #1394


The severe weather threat for Tornado Watch 401 continues.


SUMMARY...The tornado threat will continue for much of central New Jersey for the next 1-2 hours as storms approach the coast.


DISCUSSION...Convection moving eastward out of far eastern PA into central NJ continues to exhibit organized supercellular structure, and at least one confirmed tornado has been noted with this activity over the past hour. Recent surface observations across NJ show winds have backed slightly to the south/southeast, which has augmented low-level helicity over the region. This is captured well by the KDIX VWP, which exhibits strong veering in the lowest 3 km. Recent RAP soundings compare well to these observed trends and suggest upwards of 150-200 m2/s2 effective SRH is in place across the region. This wind profile, coupled with sufficient instability, will continue to support a tornado threat as storms move towards the NJ coast over the next 1-2 hours.

Mesoscale Discussion #1435


The severe weather threat for Severe Thunderstorm Watch 413 continues.


SUMMARY...A localized corridor favorable for a couple tornadoes may evolve across portions of southern Wisconsin and WW413.


DISCUSSION...As of 2150 UTC, regional radar data showed several severe storms ongoing near an MCV and modified effective front across southern Wisconsin. Along this boundary, locally backed surface winds are supporting enlarged low-level hodographs favorable for supercells. SPC mesoanalysis and regional VWPs indicated 300-400 m2/s2 of ESRH is present along the boundary while to the south, a moderately unstable airmass 2500-3000 J/kg of MLCAPE resides. Temperatures in the upper 80s and dewpoints in the 70s F will continue to support robust updraft development along the southern side of the MCV this afternoon. Given the favorable shear profiles, a corridor of greater severe threat will continue to evolve across southern portions of WW413 ahead of a tornadic supercell in Grant County Wisconsin. Here, a couple tornadoes and damaging wind gusts will be possible over the next one to two hours.

Mesoscale Discussion #1453


The severe weather threat for Tornado Watch 417 continues.


SUMMARY...Vigorous thunderstorm development, including discrete supercell structures with the potential to produce relatively short-lived tornadoes, will continue into the 7-9 PM time frame.  This could impact western and southwestern portions of the Greater Chicago metro area, before activity possibly consolidates into an organizing, southward and southwestward moving cluster.


DISCUSSION...To the south of a weak surface low/low-level cyclonic circulation centered near/east of Madison, WI, a corridor of stronger low-level surface heating and confluent low-level flow will remain the focus for vigorous thunderstorm development into the evening hours.  Mid-level temperatures above this corridor are relatively warm (including 500 mb temps around -6C), but boundary-layer moisture content is seasonably high, with surface dew points in the lower/mid 70s F.  


Beneath northwesterly mid-level flow (30-35+ kt around 500 mb) to the west of the mid-level trough axis, 30+ kt southwesterly flow around 850 mb along this corridor is contributing to sufficient shear for supercells.  While the severe hail risk appears low, the high boundary-layer moisture content coupled with modest, clockwise curved low-level hodographs have been conducive to occasional brief tornadic development, and this may remain the case another hour or two.


Into the 01-03Z time frame, at least some model output suggests that convection could begin to congeal into a small organizing cluster of storms near or to the west/southwest of the Greater Chicago area. If this occurs, stronger thunderstorm activity should tend propagate to the south and southwest, with at least some increase in potential for a strong downburst or two, while the risk for tornadoes diminishes.

Mesoscale Discussion #1454


The severe weather threat for Severe Thunderstorm Watch 418 continues.


SUMMARY...Supercells across WW418 will continue to pose a risk for all hazards. Additional development is expected over the next few hours with an increasing risk for hail/damaging winds later this evening.


DISCUSSION...Ahead of the compact upper low across the northern Plains, a cluster of supercells has become established across central North Dakota. Recent storm reports of golf ball and baseball sized hail indicate these storms continue to pose a risk for large to very large hail as they track to the north and east. Ongoing near a warm front with dewpoints in the mid 60s F, SPC mesoanalysis shows 2000-3000 J/kg of MLCAPE across much of North Dakota. Regional VWPs also show robust shear profiles with 50-60 kts of effective shear. With strong instability and vertical shear in place, the environment will remain highly favorable for supercells capable of large to very large hail and damaging wind gusts this evening. 


As the cluster of storms continues to track to the north and east, they will approach a southwest to northeast oriented warm front in the vicinity of Grand Forks, ND. Along and north of this boundary, low-level flow is strongly backed, favoring enlarged low-level hodographs. KMVX VAD data shows 200-300  ESRH in place, suggesting some potential for tornadoes if storms can remain discrete. However, additional development and continued upscale growth into one or more clusters/short line segments may shift the threat towards damaging winds later this evening. Until then, a tornado or two will remain possible near the front.

Mesoscale Discussion #1478


Concerning...Severe potential...Tornado Watch likely 


Valid 111648Z - 111845Z


Probability of Watch Issuance...95 percent


SUMMARY...The threat for several tornadoes, very large hail, and significant severe wind gusts will likely increase this afternoon. Tornado Watch issuance will be needed within an hour.


DISCUSSION...Recent visible satellite imagery shows convection is beginning to develop along and ahead of a surface cold front across northern and central WI. Pronounced large-scale forcing for ascent associated with an upper trough across the Upper Midwest will likely aid the development of at least scattered severe storms this afternoon across much of WI. The airmass south of the front is strongly unstable, with very steep mid-level lapse rates present atop a rather moist low-level airmass. Any remaining convective inhibition should dissipate within the next hour or two with continued robust diurnal heating. MLCAPE will likely reach 3500-4500+ J/kg by peak afternoon heating across this region, and enhanced mid-level west-southwesterly winds will support 50+ kt of effective bulk shear across the warm sector. Current expectations are for supercells to form initially, posing a threat for both very large (2+ inch) hail and tornadoes. This tornado threat will be aided by the continued presence of a 30-40 kt southwesterly low-level jet, which should support 0-1 km SRH of 100-200 m2/s2 and low-level updraft rotation. There is some signal in short-term guidance that these supercells may try to grow upscale into an MCS at some point this afternoon. If this were to occur, then numerous severe/damaging wind gusts, some of which could be significant, would be likely given the large buoyancy available. Regardless of eventual storm evolution, the increasing threat for supercells this afternoon will require Tornado Watch issuance within an hour.

Mesoscale Discussion #1483


The severe weather threat for Tornado Watch 424 continues.


SUMMARY...The threat for all severe hazards, including tornadoes, will continue across much of southern/central WI this afternoon.


DISCUSSION...Multiple supercells have formed this afternoon across WI along and ahead of a cold front. The environment remains very favorable for severe supercells, with MLCAPE of 2500-4000 J/kg present across this area, along with continued strong deep-layer shear owing to the upper trough and related 50-60+ kt mid-level jet present over the Upper Midwest. The greatest tornado potential in the short term should exist in a narrow southwest to northeast corridor across parts of southern/central WI, where around 100-150 m2/s2 of 0-1 km SRH is present. Indeed, a supercell in Monroe County WI has recently acquired strong low-level rotation with a corresponding CC minimum. In addition to the tornado threat, both large hail and damaging winds will remain a possibility as well. This severe wind threat may increase across parts of east-central WI over the next couple of hours if storms continue to congeal and grow upscale into a cluster.

Mesoscale Discussion #1532


The severe weather threat for Tornado Watch 441 continues.


SUMMARY...The waterspout/tornado potential over the next 1-2 hours will be highest across the western Apalachee Bay shore in the Florida Panhandle.


DISCUSSION...Latest radar and IR satellite trends show convection being focused along a confluent rain band associated with tropical storm Fred off the west coast of the FL peninsula and into Apalachee Bay. Easterly winds are advecting higher theta-e air (characterized by dewpoints in the mid to upper 70s) from the FL peninsula into the rain band, which is supporting transient convection. This trend should continue in the near term, and 150-200 m2/s2 SRH in the lowest 1-2 km (as sampled by the KTLH VWP) is allowing for periods of weak rotation with some of these storms. Although the thermodynamic environment becomes less favorable with northern and westward extent across the FL panhandle, storms propagating along the rain band and onto the western shore of Apalachee bay will pose the risk for brief waterspouts/tornadoes. Given the slow motion of the tropical storm, this band will likely remain focused south of the Tallahassee, FL - primarily across the Franklin county area - over the next 1-2 hours. The tornado threat is still expected to gradually shift northward through the rest of the day.

Mesoscale Discussion #1542


Concerning...Severe potential...Watch possible 


Valid 170713Z - 170915Z


Probability of Watch Issuance...60 percent


SUMMARY...The environment has become increasingly conducive to occasional supercell structures capable of producing short-lived tornadoes near and southwest through north of Macon, GA, and this may continue to develop northward toward areas near and southeast of the Greater Atlanta metropolitan area through daybreak.


DISCUSSION...As Tropical Storm Fred slowly migrates northward to the southwest/west of the Columbus, GA area, latest observational data and objective analysis indicate northwestward advection of moist boundary-layer air characterized by mid/upper 70s F dew points is ongoing across southeastern through central Georgia.  This has contributed to a substantive increase in boundary-layer CAPE during the past few hours, and inflow of this air is contributing to thunderstorm development within bands of convection pivoting around the northeastern periphery of the low-level cyclonic circulation center.  This coincides with where clockwise-curved low-level hodographs are maximized and supportive of occasional development and strengthening of low-level mesocyclones capable of producing tornadoes.

Mesoscale Discussion #1544


The severe weather threat for Tornado Watch 444 continues.


SUMMARY...The risk for a tornado will likely focus through the midday and into the early afternoon in two areas:  1) occasional strengthening of storm-scale rotation in the more prominent band east of the circulation center, and 2) with developing convection over west-central NC moving northwestward into a baroclinic zone.


DISCUSSION...Midday surface analysis indicates a sharpening baroclinic zone over the western Carolinas in a north-south line from near/immediately east of Spartanburg, SC northward to 35 mi northeast of Hickory, NC.  Temperatures east of the boundary have warmed into the upper 70s over SC Piedmont and slightly warmer farther north into NC with lower 80s observed near Charlotte.  A very moisture rich airmass featuring mid 70s surface dewpoints in combination with some heating will yield sufficient buoyancy for sustained strong updraft development for a couple of storms.  It seems the most vorticity rich low levels will continue to be near the boundary.  The Greer, SC 88D VAD shows an enlarged hodograph with 100-150 m2/s2 0-1 km SRH when accounting for observed storm motions.  Given the adequate buoyancy/SRH in place, a couple of supercells with an occasional tornado threat seems probable through the early and into the mid afternoon.

Mesoscale Discussion #1637


Concerning...Severe potential...Watch likely 


Valid 291007Z - 291230Z


Probability of Watch Issuance...95 percent


SUMMARY...A tornado threat will develop across southeast Louisiana and far southern Mississippi this morning. A tornado watch will need to be issued across the central Gulf Coast.


DISCUSSION...Hurricane Ida is currently located 60 statute miles south from southeast tip of Louisiana. The National Hurricane Center is forecasting Hurricane Ida to move into southeast Louisiana early this afternoon. Ahead of the center of Ida, two well-defined circular rainbands are present. The outer band will move inland across southeast Louisiana and southern Mississippi over the next 2 to 4 hours. Short lines of convection are ongoing near New Orleans and to the south of Biloxi, Mississippi within this outer band. The RAP is currently analyzing moderate instability from southeast Louisiana into southern Mississippi where MLCAPE is estimated in the 1000 to 1500 J/kg range. Precipitable water values are above 2.25 inches, which is helping to create LCL heights between 500 and 700 meters above ground level. The New Orleans WSR-88D VWP currently has 0-1 km shear near 30 kt but RAP forecast soundings gradually increase 0-1 km shear to about 40 kt by 12Z. This will make low-level shear increasingly favorable for tornadoes over the next few hours. The more discrete cells within these outer bands of Ida will have potential to become supercells and could be associated with tornadoes. For this reason, a tornado watch will be issued in the 11Z to 12Z timeframe for parts of southeast Louisiana and far southern Mississippi.

Mesoscale Discussion #1638


The severe weather threat for Tornado Watch 472 continues.


SUMMARY...Tornadoes will remain possible with the stronger cells within outer convective bands.


DISCUSSION...An initial band of storms continues to move northward across southern MS, southern AL, and the western FL Panhandle. The strongest cells continues to be across southern AL and into FL where there is access to more favorable boundary-layer theta-e. Farther northwest into MS and curling southwest across the LA state line, a region of cooler air exists which may be reducing tornado potential temporarily.


With time, higher theta-e is expected to shift westward across southern MS and much of southeastern LA, along with increasing SRH. Additional bands of convection are expected to develop into the area, most likely emanating from the instability axis currently near and south of the AL/FL Panhandles where more robust bands of convection are currently situated.

Mesoscale Discussion #1665


The severe weather threat for Tornado Watch 480 continues.


SUMMARY...A threat for brief tornadoes continues across Tornado Watch 480.


DISCUSSION...Several cells near Rockbridge to Albemarle counties in western/central VA have intensified over the past hour or so. These cells continue to exhibit periods of weak low-level rotation as they shift north/northeast. This activity is occurring in the vicinity of a surface boundary draped across the region and within a corridor of stronger low-level instability (0-3 km MLCAPE around 100-125 m2/s2). Low-level shear is somewhat less favorable with northeast extent compared to earlier this evening, but still sufficient to support rotating cells capable of brief tornadoes.

Mesoscale Discussion #1668


Concerning...Severe potential...Tornado Watch likely 


Valid 011503Z - 011730Z


Probability of Watch Issuance...95 percent


SUMMARY...Storms are likely to increase in coverage and intensity near a front from northern Virginia into New Jersey. Damaging winds and a few tornadoes appear likely.


DISCUSSION...Surface analysis shows a low over eastern WV with a front extending east/northeastward into southern NJ. Extensive clouds exist over much of the region, but relative clearing exists across eastern NC and VA toward the Delmarva. The strongest instability is coincident with the mid 70s F dewpoints near the zone of clearing. While temperatures aloft are warm, this is still resulting in substantial instability.


Low-level shear is currently maximized along and just north of the stationary front from southern PA into NJ, as well as along an axis from the WV Panhandle southward across west-central VA. 0-1 SRH values up to 100 m2/s2 exist in the higher theta-e air mass, which is sufficient for a tornado risk.


As the low continues slowly northeastward, and warm advection persists near the rain-reinforced stationary front, effective SRH is expected to concentrate from northern VA across MD, southeast PA and NJ. Showers now forming along a line from central VA into northeast NC near the instability gradient are expected to gradually deepen, and a couple supercells may evolve out of this line of convection. Otherwise, storms are likely to gradually increase in coverage and intensity east of the low as it shifts into southeast PA and NJ be evening. Both damaging winds and few tornadoes will be possible. In addition, the PA/NJ portion of the front is expected to shift north, and this may bring the severe risk toward Long Island this evening.

Mesoscale Discussion #1669


The severe weather threat for Tornado Watch 482, 483 continues.


SUMMARY...A relative maximum in tornado risk currently stretches from northeast Virginia into central and eastern Maryland.


DISCUSSION...Multiple supercells have developed within a line south of the D.C. area, with notable rotation on radar. The moist and warming air mass has lead to 2000-2500 J/kg SBCAPE, including a favorable amount of low-level CAPE as 700 mb temperatures remain tempered.


The 16Z special sounding from IAD shows an impressive low-level hodograph structure, with observed storm motions resulting in 280 m2/s2 0-1 SRH. As such, it appears RAP-based objective analysis is underestimating the shear.


The environment east/northeast of the ongoing cells remains favorable for a supercell tornado threat, bounded on the north by the stationary front.

Mesoscale Discussion #1671


The severe weather threat for Tornado Watch 482, 483 continues.


SUMMARY...A threat for a few tornadoes along with damaging wind gusts will shift northeast out of Maryland and into Delaware, southern New Jersey, and extreme southeast Pennsylvania.


DISCUSSION...Surface analysis shows a stationary front across northern MD, southeast PA and into southern NJ, with a very moist air mass to the south. Given persistent southerly surface winds impinging on this front, it is likely that sufficient elevated instability exists immediately north of the boundary to support severe storms, most likely in the form of an MCS which should travel east/northeastward. Damaging winds will be possible with such activity, with embedded circulations possible.


Otherwise, a tornado threat remains on and south of the front, where storms will have access to around 2000 J/kg SBCAPE. The tornado risk is maximized for northeastward-moving cells, providing maximum SRH per 16Z IAD sounding. Other cells moving north/northwestward ahead of the consolidating convective line may still yield strong gusts.

Mesoscale Discussion #1673


The severe weather threat for Tornado Watch 483 continues.


SUMMARY...Storms are likely to increase in coverage and spread east/northeast across New Jersey and eventually Long Island. Damaging gusts and perhaps a tornado will be possible. An additional watch could be needed later today.


DISCUSSION...A large mass of storms currently exists just north of a warm front over southeast PA, with an additional cluster moving northeastward out of MD and northern DE. The warm front currently extends east across central NJ, and has been moving north at around 8 kt. 


The conglomeration of storms over southeast PA will likely spread east along and north of the warm front, with damaging gusts possible. Shear will remain favorable for periodic supercells or a brief tornado near this boundary which is likely to affect Long Island later this evening.


Storm mode trends currently suggest that wind may become the primary risk, especially if the storms remain north of the front. However, any cells that may develop along the front itself could possibly produce a brief tornado as low-level SRH remains favorable.


**This MCD preceded the Philly metro tornadoes

Mesoscale Discussion #1674


The severe weather threat for Tornado Watch 483 continues.


SUMMARY...Confirmed tornadoes have occurred both north and south of Philadelphia. The environment will continue to support tornadic potential, particularly for areas in southern/central New Jersey.


DISCUSSION...Supercells moving northeast along the slowly northward advancing warm front have recently produced tornadoes as confirmed by TDS signatures from KDIX. The northern storm is now moving Somerset County, NJ, with the southern storm moving through Camden/Burlington Counties (NJ). Given objectively analyzed 0-1 km effective SRH over 200 m2/s2 (confirmed by KDIX VWP), supercells that can maintain strength are expected to continue posing a threat for tornadoes. At present, the Camden/Burlington storm is moving within an airmass unaffected by much precipitation and should have the greatest tornado potential for the next 1-2 hours.

Mesoscale Discussion #1820


Concerning...Severe potential...Watch likely 


Valid 101904Z - 102100Z


Probability of Watch Issuance...80 percent


SUMMARY...Increasingly widespread and intensifying thunderstorm development appears probable in a corridor across southwestern through north central Oklahoma, including the Greater Oklahoma City area, as well as adjacent portions of northwest Texas and south central Kansas, by 5-7 PM.  Some of this activity will pose a risk for severe hail initially, with increasing potential for a few tornadoes by early evening.


DISCUSSION...A weak surface cold front has stalled south of Wichita, KS, south-southwestward into areas near/east of Childress, TX, where a surface low is beginning to form near the nose of a corridor of stronger boundary-layer heating and deeper mixing, beneath a plume of capping elevated mixed-layer air across the southern Great Plains.  A dryline is becoming better defined east and south of the surface low, and boundary-layer moisture is gradually increasing along and ahead of the front to the northeast of the surface low.


Due to the initially modest moisture relatively to the warmth of the elevated mixed-layer, latest objective analysis indicates that warm sector boundary-layer CAPE remains fairly weak (500-1000 J/kg). However, it appears that this will begin to substantively change during the next few hours, as the leading edge of mid-level forcing for ascent and cooling now overspreading the Texas Panhandle/South Plains progresses eastward.


Weakening inhibition and increasing mixed-layer CAPE likely will coincide with strengthening deep-layer shear accompanying a 50-70+ kt southwesterly 500 mb jet streak, contributing to an environment conducive to organized severe thunderstorm development.  It seems probable that this will include a rapidly upscale growing line of storms along/ahead of the front by early evening.  However, initial storm development may include isolated to scattered discrete supercells, particularly in a possible cluster near/northeast of the surface low and dryline across southwestern Oklahoma.


South-southwesterly flow in the 850-700 mb layer is initially rather modest, but forecast to strengthen to 30-40+ in the vicinity of the intensifying convective development, generally along the Interstate 44 and 35 corridors (near and southwest through north of the Oklahoma City metropolitan area) by around 00-01Z.  This will contribute to enlarging low-level hodographs supportive of strengthening low-level mesocyclones, posing a risk for tornadoes, in addition to severe hail.

Mesoscale Discussion #1822


The severe weather threat for Tornado Watch 517 continues.


SUMMARY...Initiation of discrete storms is becoming more likely in the vicinity of Frederick, OK within the next 1-1.5 hours. The threat for tornadoes is increasing in southwest Oklahoma into parts of central Oklahoma.


DISCUSSION...Towering cumulus continues to develop south of Frederick, OK. The strongest pressure falls in the last few hours have occurred in this vicinity. Confidence is increasing in storm initiation within the next 1-1.5 hours. Given the backed surface winds and over 50 kts of effective shear, initial storm mode will likely be supercellular. KFDR VWP has begun to show an increase in low-level SRH recently as well. Storms that form in this region would pose the greatest tornado risk over the next few hours.

Mesoscale Discussion #1838


Concerning...Outlook upgrade 


Valid 121929Z - 122000Z


SUMMARY...An upgrade to Category 4/Moderate risk will be introduced in the 20Z Day 1 Convective Outlook to reflect a greater risk for strong tornadoes.


DISCUSSION...The latest high-resolution/convection allowing model guidance consensus has been generally trending upward in the intensity and longevity of deep, moist convection over portions of the southern High Plains. Potential exists for multiple discrete/semi-discrete supercells to develop ahead of a Pacific front late this afternoon/evening. These storms are expected to progress eastward into an ambient environment characterized by very strong low-level shear, resulting in large, curved hodographs and effective SRH values exceeding 400 m2/s2, especially across portions of southwest KS/northwest OK/far northeast TX Panhandle. Here, potential exists for at least a few intense, cyclical tornadic supercells to develop, and a long-tracked tornado or two cannot be ruled out. As such, portions of the central Plains will be upgraded to Category 4/Moderate risk in the upcoming 20Z Day 1 Convective Outlook.

Mesoscale Discussion #1839


Concerning...Severe potential...Tornado Watch likely 


Valid 122008Z - 122145Z


Probability of Watch Issuance...95 percent


SUMMARY...Strong ascent ahead of an advancing upper low will support rapid destabilization and storm development late this afternoon and into this evening. Supercells with all hazards including tornadoes are possible. A tornado watch is likely late this afternoon.


DISCUSSION...As of 1955 UTC, a well-defined upper low was located on WV imagery near the Four Corners region moving east. To the south of the low, an 80-100 kt mid-level speed max was observed rounding the base and ejecting into southern CO. To the north and east of the low, strong ascent (90-120 DM 12 hr H5 height falls) is supporting widespread precipitation across the central and northern Rockies. In response to the powerful dynamics aloft, already strong low-level pressure gradients are forecast to strengthen rapidly allowing a relatively warm/moist surface airmass to advect ahead of the dryline/surface trough supporting destabilization late this afternoon.


Mid and lower 50s F surface dewpoints at the nose of deeper surface moisture, have already been observed across southwestern KS as far north as TQK. Continued warm/moist advection beneath the cold-core of the upper low will support rapid destabilization (MLCAPE values of 500-1250 J/kg) by 23-01z given steep mid-level lapse rates near 8.5 C/km. Late afternoon/early evening model soundings also show very strong and veering wind profiles developing beneath the mid-level jet, with largely boundary-normal effective shear values of 60-70 kt supportive of discrete supercells. Low-level shear is also likely to be strong beneath a 50-60 kt low-level jet. Model soundings show large looping hodographs (ESRH 300-400 M2/s2) favorable for strong low-level mesocyclone development. Given the overall parameter space and potential for strong supercells, a risk for tornadoes (some significant), large hail, and damaging winds appears likely to develop by 22-00z. 


Latest observational trends suggest hi-res guidance remains too cool and dry across much of the High Plains where rapid warming/moistening is occurring. This lends high confidence in eventual destabilization of the airmass as the upper low approaches late this afternoon. Deep convection should gradually evolve out of the initial updrafts ongoing in the elevated cumulus field across eastern CO. Weaker buoyancy and storm motions more parallel to the northern sections of the dryline suggest initial storm mode may remain linear, though a gradual transition to more isolated convection is expected with southern extent. Fast-moving long-track supercells capable of all hazards should evolve rapidly and intensify as they move through the narrow, but unstable and strongly sheared warm sector after dark. Given the potential for significant severe weather, a tornado watch will likely be needed late this afternoon.

Mesoscale Discussion #1840


Concerning...Severe potential...Tornado Watch likely 


Valid 122014Z - 122245Z


Probability of Watch Issuance...80 percent


SUMMARY...A few supercells may develop through evening, from the eastern Texas Panhandle into far western Oklahoma. Tornadoes, perhaps strong, and very large hail will be possible.


DISCUSSION...Surface analysis shows a front extending from northern TX into southwest OK which is becoming more diffuse with heating. This boundary separates a cooler/capped air mass over much of OK from a destabilizing air mass over northwest TX and into the TX Panhandle. Meanwhile, a dryline stretches from north to south across the TX Panhandle and South Plains.


Visible satellite shows stable billow clouds north of the boundary, but these are gradually eroding from south to north as temperatures warm into the lower 80s F. A growing CU field is also evident over northwest TX, where MLCAPE is in the 1500-2000 J/kg range. Backed surface winds on the cool side of the boundary are contributing to 100-150 m2/s2 0-1 km SRH per FDR VWP.


Although convergence is currently weak, it is expected to increase around 00Z and into the evening as the dryline eventually pushes east with the upper trough. A few more hours of air mass modification will occur, including moistening. In addition, the low-level jet will continue to increase to over 50 kt, further enhancing shear.


Assuming a cell or two can form, they should quickly acquire rotation, with tornadoes and hail likely. Any lone cells that can maintain access to the warm side of the boundary will have the potential for a strong tornado.

Mesoscale Discussion #1869


Concerning...Severe potential...Watch unlikely 


Valid 160616Z - 160745Z


CORRECTED FOR GRAPHIC ERROR


Probability of Watch Issuance...20 percent


SUMMARY...A weak, brief tornado or two may occur over parts of southern Ohio over the next couple of hours.


DISCUSSION...A persistent supercell near the southeastward-advancing cold front has produced several moderate mesos with radar-indicted tornado debris signatures in Highland and Ross counties over the past hour. This cell appears to be located near a meso low and/or MCV, which is likely supporting locally enhanced SRH. Furthermore, this cell is within an area of relatively stronger low-level instability and surface vorticity as noted in latest mesoanalysis. Downstream surface dewpoints are in the low/mid 60s with locally backed surface winds. This should continue to support at least low potential for sporadic re-intensification of ongoing convection and some threat for weak/brief spin-ups to occur over a relatively small area. The broader environment appears unlikely to support a more widespread threat or increasing convective coverage. While a tornado watch is not expected at this time, trends will continue to be monitored.

Mesoscale Discussion #1881


Concerning...Severe potential...Watch unlikely 


Valid 212125Z - 212330Z


Probability of Watch Issuance...20 percent


SUMMARY...The tornado risk will likely continue for another hour or so (thru 600-630 pm EDT) and decrease towards sunset and likely be very limited after sunset.


DISCUSSION...Radar imagery from Cleveland's 88D shows a broken band of supercells immediately ahead of a strong mid-level vorticity maximum moving east across the southern Great Lakes.  Surface temperatures have warmed into the low-mid 60s with dewpoints near 60 F. RAP forecast soundings indicate 100-250 J/kg MLCAPE with a relatively straight hodograph yielding 150-225 m2/s2 0-1 km SRH. The current expectation is for a continuation of the tornado risk for the next hour or so given the sufficient buoyancy in place across northeast OH.  However, as the boundary layer begins to cool this evening towards sunset and temperatures fall into the 60-62 deg range, storm-scale rotation will gradually become more intermittent and less intense.  The tornado risk will correspondingly lessen as supercell rotation weakens.  The tornado risk will further diminish after sunset as cooling further increases convective inhibition and supercell rotation becomes more marginalized.

Mesoscale Discussion #1882


Concerning...Severe potential...Watch unlikely 


Valid 212356Z - 220200Z


Probability of Watch Issuance...20 percent


SUMMARY...The threat for a couple of tornadoes is expected to persist for a couple more hours before storms weaken and the severe threat gradually diminishes. Given the expected short duration tornado threat, a Tornado Watch issuance remains unlikely.


DISCUSSION...Multiple discrete/semi-discrete supercells continue to exhibit instances of strong low-level rotation, from Butler County PA to Ohio County WV. Multiple TDS signatures were noted with some of these storms in the past few minutes via KPBZ dual-polarimetric radar data. These storms continue to rotate within an environment characterized by weak buoyancy (MLCAPE barely reaching 500 J/kg MLCAPE), but with strong low-level shear. Specifically, PBZ VAD profiler data have shown consistent elongated hodographs with 200+ 0-1km SRH, with METAR observations also showing some localized backing of the surface winds across southwest PA. As such, storm organization and periods of low-level rotation/brief tornadoes will likely continue for a couple more hours, before boundary-layer stabilization results in a gradual waning of the severe threat. A Tornado Watch issuance is not expected.

Mesoscale Discussion #1888


Concerning...Severe potential...Tornado Watch likely 


Valid 241740Z - 242015Z


Probability of Watch Issuance...95 percent


SUMMARY...The threat for tornadoes, large hail, and severe wind gusts will increase as storms develop and intensify this afternoon. Tornado Watch issuance will be needed.


DISCUSSION...A low-amplitude shortwave trough will continue moving eastward across the central Plains and MO Valley this afternoon. Large-scale ascent preceding this feature is already supporting isolated convection ahead of a cold front just east of the KS/MO border. Latest surface observations show a warm front extends eastward across MO. With a surface low progged to develop across northern MO this afternoon, this warm front may lift northward a little bit more across MO over the next few hours. Diurnal heating of a moist low-level airmass across this region along with steep mid-level lapse rates will likely support 1500-2000 J/kg of MLCAPE by mid to late afternoon. A veering and strengthening wind profile at both low and mid levels will foster 40-50 kt of effective bulk shear, which is more than sufficient for supercells.


Current expectations are for surface-based storms to develop along or just ahead of the cold front across western MO by 19-20Z (2-3 PM CDT). Some short-term guidance suggests that other storms may initiate across the open warm sector as well. Supercells will likely be the dominant storm mode initially this afternoon, as sufficient cross-boundary flow aloft is present along and ahead of the cold front. Given the steep mid-level lapse rates present, large hail should occur with these supercells. Low-level shear also appears strong in recent VWPs from KEAX/KSGF. Effective SRH in the 200-300 m2/s2 range will likely foster low-level rotation and potential for tornadoes with any supercells. The best low-level shear and related tornado potential may exist along the warm front, where low-level winds will be backed to a more east-southeasterly direction. A couple of these tornadoes, especially across MO, could be strong since the thermodynamic and kinematic environment both appear rather favorable. With time, one or more broken lines of supercells and/or small clusters are expected to advance eastward across MO and into parts of west-central IL. The severe wind threat may eventually increase, especially if storms develop more linear characteristics versus a broken line of supercells. Regardless of eventual convective evolution, the increasing severe threat this afternoon will require Tornado Watch issuance within the next couple of hours (likely by 2-3 PM CDT).

Mesoscale Discussion #1893


The severe weather threat for Tornado Watch 531 continues.


SUMMARY...The threat for severe storms, including tornadoes, continues across Tornado Watch 0531 in central MO, and is expected to persist through the remainder of the evening. The greatest short term threat is associated with storms immediately ahead of the cold front and in proximity to the warm front, though the severe threat may increase further south with time.


DISCUSSION...Multiple sustained semi-discrete supercell structures are in progress across portions of north-central into central MO immediately ahead of a cold front and within proximity to a diffuse warm front. In addition, storms are also attempting to mature further south along the cold front into southwest MO, as well as with a second confluence zone east of SGF. Tornadoes have been reported over the past few hours across northern/central MO with storms closer to the warm front, where latest METAR observations depict more backed surface flow. These storms have the greatest threat of continued tornado potential in the short term. 


The low-level jet is expected to intensify going into the evening hours across portions of central into eastern MO. 2154Z SGF VWP showed over 200 m2/s2 SRH, and these values are expected to gradually increase this evening. As such, a tornado threat may develop with any sustained supercell structures that manage to develop in southern MO. In addition, severe hail and damaging rear-flank downdraft winds may also accompany any mature supercells as well.

Mesoscale Discussion #1895


The severe weather threat for Tornado Watch 533 continues.


SUMMARY...The greatest tornado threat is currently over southeastern Missouri, and is expected to shift into southern Illinois.


DISCUSSION...A trio of supercells currently extends from Ste. Genevieve into Reynolds County MO, with strong mesocyclones noted on radar. Storm mode appears complex with substantial precipitation ahead of the circulations. 


These storms are currently near the instability axis, with MLCAPE around 1500 J/kg. Dewpoints rapidly decrease toward the Wabash/Lower Ohio Valleys, but favorable instability should remain in place toward the MS River and into parts of southern Illinois. Here, 0-1 SRH exceeds 300 m2/s2, which is quite favorable for tornadoes and supercells producing damaging wind gusts.

Mesoscale Discussion #1911


Concerning...Severe potential...Watch likely 


Valid 271236Z - 271400Z


Probability of Watch Issuance...80 percent


SUMMARY...Discrete thunderstorm development is ongoing and likely to continue across the region into mid morning.  It appears that this will include the evolution of a few supercell structures which may begin to pose a risk for tornadoes.


DISCUSSION...Thunderstorm activity on the leading edge of the southeastward advancing, convectively generated surface cold pool has yet to show signs of appreciable intensification, and the window of opportunity for this to occur appears to be narrowing, with it on track to reach mid/upper Texas coastal areas by or shortly after 15Z.  However, this activity is now preceded by scattered discrete thunderstorm development, likely rooted within the seasonably moist and moderately unstable boundary layer, near upper Texas and southwestern Louisiana coastal areas.  These storms probably have been supported by forcing associated with weak low-level warm advection, with at least one cell with a sustained low-level mesocyclone offshore east of Galveston.  


The isolated supercell may advance inland across coastal areas southwest of Beaumont/Port Arthur during the next hour or two, and similar additional development near coastal areas appears at least possible through 14-15Z.  Although cloud cover may slow boundary-layer destabilization inland across southwestern into south central Louisiana coastal areas, strengthening of southerly 850 mb flow (in excess of 30 kt) is ongoing, and will contribute to enlarging clockwise curved low-level hodographs.

Mesoscale Discussion #1912


 The severe weather threat for Tornado Watch 540 continues.


SUMMARY...The greatest threat for tornadoes through 16Z will persist with discrete storms developing from southeast TX and possibly far southwest LA.


DISCUSSION...Early this morning a warm front extends through southwest LA north of Lake Charles into southeast TX near Jasper, then farther northwest where it intersects the squall line which extends southward through the Houston metro area and beyond. The warm sector to the south and east of these boundaries is very moist with low to mid 70s F dewpoints along with temperatures in the upper 70s F. The 12Z RAOBs and latest objective analysis show the atmosphere in this area to be moderately unstable with around 1500 J/kg MLCAPE. VWP data from Lake Charles also indicates sizeable low-level hodographs with 250-300 m2/s2 storm relative helicity based on current storm motions. This strongly sheared, low-LCL environment will remain favorable for low-level mesocyclones and tornadoes next couple hours as discrete supercells continue moving northeast through the warm sector. Some interaction with the warm front is also likely, potentially augmenting the tornado threat.


Farther west, damaging wind will remain the primary threat along the squall line, but a couple of brief tornadoes cannot be ruled out with any embedded mesovortices.

Mesoscale Discussion #1914


The severe weather threat for Tornado Watch 540 continues.


SUMMARY...Threat for a few tornadoes (a couple of which could be strong) remains relatively high across southeast TX into southwest LA through at least 18Z.


DISCUSSION...Supercell with a history of tornadoes has crossed into southwest LA and will remain in a favorable environment for additional tornadoes next couple hours. Other semi-discrete storms farther west in southeast TX might also become better organized, but some of this activity is being overtaken by the squall line. A couple storms are developing in closer proximity to the warm front over southwest LA, and might evolve into supercells as they continue northeast. Low-level hodographs remain large within a low LCL and moderately unstable environment, suggesting the threat for tornadoes will persist next couple hours, especially with discrete or semi-discrete storms in warm sector and in proximity to the warm front. 


Otherwise, isolated strong to damaging wind gusts and brief QLCS tornadoes remain possible with embedded organized structures in the squall line.

Mesoscale Discussion #1915


The severe weather threat for Tornado Watch 540 continues.


SUMMARY...Threat for damaging wind and tornadoes including potential for a couple of strong tornadoes should persist over southern LA, spreading east through southeast LA and southern MS during the afternoon. A new tornado watch will likely be needed for this area by 19Z.


DISCUSSION...A line of storms with embedded bowing segments and some supercell structures continues moving through western LA at around 35 kt. East of this line the warm sector continues to expand northward south of a warm front that extends from southeast through north central LA. A very moist boundary layer is in place south of this front with mid 70s F dewpoints, and diabatic warming has boosted surface temperatures into the low to mid 80s F supporting up to 2000 J/kg MLCAPE. Several northwest-southeast oriented convergence bands are evident on visible imagery extending into southern LA from the Gulf. The 18Z RAOB from Slidell modified for surface conditions in warm sector indicates minimal inhibition. This suggests that, in addition to the arrival of the line of storms, the potential will exist for discrete storms develop as the boundary layer continues to destabilize. The low-level jet is forecast to undergo further strengthening, supporting large hodographs with 0-1 km storm relative helicity from 250-350 m2/s2. Threat for damaging wind and tornadoes will persist through the remainder of the afternoon into early evening in this region.

Mesoscale Discussion #1917


The severe weather threat for Tornado Watch 542 continues.


SUMMARY...Threat for damaging wind and tornadoes including potential for a couple of strong tornadoes will persist across southeast LA and far southern MS into the early evening.


DISCUSSION...Warm front is moving northward and currently extends from southeast LA near New Orleans northwest into southwest MS. Numerous discrete showers and a few supercells continue developing across southeast LA within the weakly capped warm sector along and south of the warm front where the atmosphere remains moderately unstable. The Slidell VWP indicates a large hodograph with veering winds in the lowest 1 km supporting up to 350 m2/s2 storm relative helicity along the low level jet corridor. Some of the pre-frontal convection will likely evolve into mature supercells and become capable of producing tornadoes, especially as they interact with the warm front. Otherwise, embedded bowing segments, mesovortices and occasional supercells continue to be observed within the squall line, supporting a threat for damaging wind and QLCS tornadoes.

Mesoscale Discussion #1945


Concerning...Severe potential...Watch likely 


Valid 131707Z - 131900Z


Probability of Watch Issuance...80 percent


SUMMARY...Showers and thunderstorms are expected to intensify across the region, spreading from near northern Mid Atlantic coastal areas into southern New England, accompanied by increasing risk for potentially damaging wind gusts and perhaps a couple of tornadoes through late afternoon.


DISCUSSION...Although details differ considerably among the various models, it seems probable that surface low pressure will begin to consolidate across parts of central New Jersey into the western Long Island vicinity by mid afternoon, before deepening while continuing to track east-northeastward across southeastern New England through 22-00Z. This is expected in response to strengthening large-scale forcing for ascent, ahead of a vigorous short wave trough currently pivoting across the northern Virginia/central Maryland vicinity.


It appears that this will include intensifying lift within a corridor along and ahead of an associated cold front, preceded by at least weak destabilization within an expanding warm sector across parts of southeastern New England.  It is uncertain whether destabilization will be sufficient to support discrete storm development ahead of the east-northeastward surging cold front, but the evolution of at least a narrow line of low-topped convection seems probable in response to the enhanced mesoscale lift.


Likely located along/just north of a belt of 70-90+ kt flow around the 500 mb level, cloud bearing layer shear will be quite strong and more than sufficient to contribute to organized convection with the potential to produce small hail and potentially damaging wind gusts. Low-level wind fields are initially relatively modest, with pre-frontal southerly 850 mb flow still around 30 kt, and this could slow the development of increasing potential for severe wind gusts. However, guidance generally indicates that substantive further strengthening of this flow to 40-50+ kt is possible, particularly by late afternoon across parts of eastern Long Island into southeastern New England, where enlarging low-level hodographs might become conducive to a risk for tornadoes, in addition to increasing potential for severe wind gusts.

Mesoscale Discussion #1978


Concerning...Severe potential...Watch likely 


Valid 101935Z - 102145Z


CORRECTED FOR TYPO


Probability of Watch Issuance...95 percent


SUMMARY...Discrete supercell development appears increasingly probable by 4-6 PM CST, accompanied by the risk for severe hail and tornadoes, including increasing potential for a couple of strong tornadoes by early evening.


DISCUSSION...A short wave impulse of subtropical eastern Pacific origin continues to accelerate northeastward across Kansas and Oklahoma, and is forecast to reach the mid/lower Missouri Valley vicinity by early evening.  Mid/upper forcing for ascent and elevated moisture return preceding this feature have contribute to weak high-based convection and light rain in a corridor across eastern Oklahoma into the lower Missouri Valley, while low-level moisture from the Gulf of Mexico gradually deepens across the lower Mississippi Valley into parts of the southeastern Great Plains.  The deeper low-level moisture return is being aided by a branch of stronger southerly flow across the northwestern Gulf coast vicinity into the Ozark Plateau.  This appears to include a 40-45 kt speed maximum around 850 mb, across the upper Texas coastal plain into the Ark-La-Tex vicinity.


Through 21-00Z, model output continues to generally indicate that this speed maximum will rapidly propagate northeastward into the Ozark Plateau through middle Mississippi/lower Ohio Valley vicinity, while strengthening to 50+ kt in a corridor from near Little Rock AR into the Missouri Bootheel vicinity.  It appears that deepening boundary-layer moisture and increasing mixed-layer CAPE along this corridor will coincide with weakening inhibition associated with a transition from broadly anticyclonic to cyclonic mid-level flow. This is expected to allow for the initiation of at least scattered discrete storm development, as southwesterly flow in the 700-500 mb layer also strengthens to 60-80+ kt.


This regime likely will become increasingly conducive to the development of supercells, with the potential to produce severe hail initially, along with at least some risk for tornadoes.  Backing of surface winds toward a south to south-southeasterly component by 00Z may gradually contribute to enlarging, clockwise-curved low-level hodographs increasingly conducive to tornadoes, a couple of which may become strong.

Mesoscale Discussion #1982


The severe weather threat for Tornado Watch 552 continues.


SUMMARY...A slow increase in storm intensity/coverage is expected over the next 1 to 2 hours.


DISCUSSION...Initial storms which developed near Little Rock have not shown much organization thus far. In addition, weak cellular convection is developing across much of the Mississippi River region. However, a strong capping inversion, sampled by the 19Z LZK RAOB is likely limiting more robust storm development thus far. As heights continue to fall this evening, expect these warmer mid-level temperatures to erode further and expect greater storm coverage and intensity. Once mature supercells can develop, all severe hazards remain possible as the environment remains favorable with 0 to 1 km shear now in excess of 35 knots per KLZK VWP.

Mesoscale Discussion #1984


The severe weather threat for Tornado Watch 553 continues.


SUMMARY...The severe threat appears to be gradually increasing across portions of central Missouri. Large hail and damaging wind gusts appear to be the primary threats, though a few tornadoes are also likely, especially across eastern Missouri later this evening.


DISCUSSION...Deep-moist convection has recently initiated across portions of southwest MO, just northwest of SGF within the past hour. These storms are developing along the western fringes of a moist warm sector, where near 60 F surface dewpoints are overspread by 7 C/km mid-level lapse rates (evident via 22Z mesoanalysis and previously noted by the 19Z SGF observed sounding). While the surface winds are somewhat veered, the 21Z SGF VWP showed a modestly curved but long hodograph depicting well over 300 m2/s2 SRH in both the 0-1 km and 0-3 km layers. 


As deep-layer ascent increases across the area and convective inhibition continues to wane, additional storms are expected to develop over the next several hours. A mixed mode of linear segments and semi-discrete storms are expected, with all severe hazards (including a couple of tornadoes) likely. The best chance for tornadoes will be later this evening across eastern MO as the more mature storms progress farther east into the LLJ axis, where low-level shear is expected to be strongest and where MLCAPE may exceed 1000 J/kg.

Mesoscale Discussion #1985


Concerning...Severe potential...Tornado Watch likely 


Valid 102352Z - 110115Z


Probability of Watch Issuance...95 percent


SUMMARY...A new tornado watch is needed downstream of tornado watch 552.


DISCUSSION...Warm air advection showers have started producing lightning across portions of southern Illinois and western Kentucky. Expect a slow increase in storm coverage and intensity across this region. This activity (including a tornado warned storm entering Calloway County, Kentucky) will move east of tornado watch 552 in the next 30 to 60 minutes. The HPX VWP shows a very favorable low-level shear environment with 0-1 km SRH around 400 m2/s2 indicating the potential for strong tornadoes. Therefore a downstream tornado watch will be needed. The eastward extent of the threat will be limited due to decreasing instability, but at least some threat is expected to near I-65. This area will likely need to be in a watch for an extended period due to multiple rounds of convection continuing for most of the night.

Mesoscale Discussion #1986


The severe weather threat for Tornado Watch 552 continues.


SUMMARY...Locally higher tornado threat potentially materializing with a maturing supercell across northeast Arkansas. Potential exists for this supercell to become long-lived, with sustained/strong tornadoes possible over the next few hours.


DISCUSSION...KLZK, KNQA, and MRMS mosaic radar data all depict an intense supercell in progress across the Jackson/Woodruff County AR area, where deep-layer ascent and LLJ intensity both continue to increase in magnitude. Latest LZK and NQA radar data also depicts a possible TDS, suggesting that the supercell may have already produced a tornado. The 00Z LZK sounding shows that the convective inhibition above the boundary layer has eroded, with a moist and unstable boundary layer likely advecting ahead of the ongoing storm. The 00Z sounding, along with the 2352Z NQA VWP shows a relatively long/curved hodograph with 0-1 and 0-3 km SRH at/over 300 m2/s2. Low-level shear is only expected to increase with further intensification of the LLJ over the MS river. Furthermore, several of the recent HRRR runs have also depicted a long-tracked supercell across this region. As such, this supercell may obtain a steady-state structure, with additional tornadoes (some strong) potentially accompanying this storm through early evening.

Mesoscale Discussion #1988


The severe weather threat for Tornado Watch 553 continues.


SUMMARY...The damaging wind and tornado threat is increasing across eastern Missouri and western Illinois, including the St. Louis Metro area.


DISCUSSION...A line of storms has organized across central Missouri and is moving quickly east toward the Mississippi River. Within this line are several embedded supercells with some low-level rotation evident from the KLSX WSR-88D. The storm with the coldest cloud tops is currently moving toward St. Louis. Therefore, this portion of the line in particular may have a greater severe wind/tornado threat over the next 1 to 2 hours, especially given the backed surface flow and around 500 m2/s2 0-1 km SRH from the KLSX VWP.

Mesoscale Discussion #1991


The severe weather threat for Tornado Watch 552, 555 continues.


SUMMARY...An uptick in the severe threat, including strong tornadoes, appears evident across southwest into east-central Arkansas. The locally higher tornado threat may persist with the more dominant supercells for at least a few hours.


DISCUSSION...Multiple storms, including sustained supercells, have recently organized across portions of central and eastern Arkansas, with a discrete supercell also entering far southwest Arkansas. MRMS mosaic radar shows intense low-level rotation tracks associated with the more dominant supercells just north of LZK, and these storms are expected to progress across a moist, unstable/minimally capped environment. The latest VWPs from SHV to NQA depict long, curved hodographs given the presence of a broad, intense LLJ overspreading the area. These VWPs and 01Z mesoanalysis depict 0-1 km and effective SRH in the 250-400 m2/s2 range, supporting the risk for sustained, strong tornadoes across southwest into eastern AR for at least the next few hours.

Mesoscale Discussion #1992


The severe weather threat for Tornado Watch 552 continues.


SUMMARY...A strong to potentially violent tornado is ongoing in far northeastern Arkansas and is expected to persist.


DISCUSSION...A mature and very strong supercell in northeast Arkansas is currently producing a very strong to potentially violent tornado. The downstream airmass remains very favorable with dewpoints near 70, strengthening/backing surface flow, and 0-1 km SRH in excess of 400 m2/s2 per KNQA VWP. This is yielding STP around 5. Given the favorable downstream environment with no convection to disrupt this storm, expect the significant tornado threat to continue for at least a few more hours as this discrete, long-track supercell continues northeast.

Mesoscale Discussion #1994


The severe weather threat for Tornado Watch 554 continues.


SUMMARY...The severe threat continues across Tornado Watch 554, with a local uptick in tornado potential possible with any discrete supercells that can become sustained.


DISCUSSION...Multiple supercell structures with transient low-level rotation have been progressing across northern portions of Tornado Watch 554 over the past couple of hours. Recently, KHPX radar data suggests a relatively deep mesocyclone has developed with a supercell across Muhlenberg County, KY, likely due to increased low-level shear as the axis of a strong LLJ overspreads the region, and as richer moisture continues to advect into the region in tandem with stronger deep-layer ascent. As such, a local uptick in tornado potential may be realized over the next couple of hours with the more isolated supercells that persist in the LLJ axis. Also, a long-lived supercell with a long-tracked, intense tornado is also approaching Tornado Watch 554, and is expected to approach the western bounds of the watch in the next couple of hours. Given that modest instability and strong low-level shear are expected to remain in place, a potentially significant tornado threat may manifest in far southwest KY.

Mesoscale Discussion #1996


The severe weather threat for Tornado Watch 552, 553, 557 continues.


SUMMARY...The severe threat continues across Tornado Watches 552, 553 and 557. A locally higher tornado threat may evolve with a more dominant storm at the southern end of a line of storms.


DISCUSSION...Multiple linear thunderstorm segments with embedded supercell structures have recently congealed into a more coherent squall-line structure across central and southern Illinois. Storms within this squall have a history of producing damaging gusts over 70 mph as well as isolated tornadoes. Widespread 60F dewpoints overspread by 6-7 C/km mid-level lapse rates are contributing to 1000 J/kg MLCAPE per 02Z mesoanalysis, amid minimal convective inhibition. The latest mesoanalysis shows widespread effective bulk shear exceeding 80 kts with ILX and PAH VWPs depicting long, curved hodographs (contributing to 300-500 0-1 km SRH). Given the impressive shear profiles, damaging gusts and tornadoes will remain a concern for at least a few more hours. 


At the southern end of the line, more dominant supercell structures have produced TDSs, and are progressing across an unimpeded low-level airmass, characterized by mid 60s F dewpoints. The impressive low-level shear, adequate moisture, and open warm sector may support a locally higher tornado threat with these storms, and a strong tornado is possible.

Mesoscale Discussion #1997


The severe weather threat for Tornado Watch 557 continues.


SUMMARY...A strong tornado threat is expected to persist for the next 1 to 2 hours across central and east-central Illinois.


DISCUSSION...The supercell on the southern edge of a line of storms moving across central Illinois has produced several tornado debris signatures so far. This portion of the line will remain the favored location for tornadoes given the lack of storm interference, low to mid 60s dewpoints, and very strong low-level shear (0-1 km SRH in excess of 600 m2/s2 per both ILX and VWX VWP). In addition, this environment will support the potential for strong tornadoes, especially as the storm inflow remains uninhibited.

Mesoscale Discussion #1999


The severe weather threat for Tornado Watch 552, 554 continues.


SUMMARY...A strong to potentially violent tornado is ongoing and expected to continue for at least another hour.


DISCUSSION...A strong supercell with a history of a long-track tornado with intense to potentially violent damage has recently intensified once again across southwest Kentucky. Latest radar and environmental analysis give high confidence that an intense to potentially violent tornado has occurred across southwest Kentucky. The radar presentation of this storm continues to be extremely favorable for continued intense, long-lived tornadoes. Nearby convection has mostly dissipated which may allow a more steady-state to continue as it moves northeast. The downstream environment remains very favorable with upper 60s to low 70s dewpoints and backed surface winds with STP around 5 to 6. Eventually, expect storm activity to the west to catch this supercell, but until that happens, continued strong to potentially violent tornadic damage is expected to continue along its path.

Mesoscale Discussion #2003


The severe weather threat for Tornado Watch 554 continues.


SUMMARY...Strong to intense tornado damage is expected to continue across portions of western Kentucky.


DISCUSSION...The long-track supercell, now entering Hopkins county, Kentucky, has now had a nearly continuous TDS for over 3 hours with an average vRot over 70 knots. The radar presentation and downstream environment does not show any sign of weakening this storm in the near term. In fact, recent observations ahead of this supercell have shown temperature increases of 2 to 3 F and dewpoint increases of 2 to 3F. This, combined with the cooling temperatures aloft, has actually increased instability ahead of this storm over the last 2 hours. Warm sector winds have veered slightly in the last hour which has reduced low-level shear slightly. However, there is still significant turning between the surface and the southwesterly low-level jet, and therefore, despite this slightly weaker shear, it likely won't have much of an impact on storm tornadic potential. 


The likely catalysts for weakening this long-lived tornadic supercell will be eventual movement into low to mid 60s dewpoints and weaker instability, or storm interference as the storms to the west catch up with the lead supercell. Neither of these are expected to have an impact in the next hour, but may bring some reprieve after 06Z.

Mesoscale Discussion #2006


The severe weather threat for Tornado Watch 554 continues.


SUMMARY...A significant tornado threat is materializing across northern Tennessee and southern Kentucky.


DISCUSSION...A cluster of storms has produced occasional tornadoes as it moved across eastern Arkansas and western Tennessee, but storm interference and a messy storm mode so far has precluded a more long-lived, strong tornado threat. However, a cell, now in Henry County, Tennessee, has emerged ahead of this line and has a favorable airmass ahead of it. MLCAPE around 1000 to 1200 J/kg and 0-1 km SRH around 300 m2/s2 per OHX VWP suggest strong tornadoes will be possible. As long as this storm inflow remains unimpeded, it will likely pose a threat for strong tornadoes.

Mesoscale Discussion #2008


The severe weather threat for Tornado Watch 554 continues.


SUMMARY...A strong tornado threat continues across portions of northern Kentucky.


DISCUSSION...Storm interference from new cells merging has finally disrupted the persistent very strong low-level mesocyclone with the long-lived supercell now entering Breckenridge County, Kentucky. However, while this has weakened the intensity of the updraft and low-level rotation, a strong tornado with around 50 to 55 knot Vrot and a TDS is still present. Mid 60s dewpoints have advected ahead of this storm and therefore, adequate instability remains for strong tornado development given the 350 to 400 m2/s2 0-1 km SRH per the KLVX VWP. Therefore, while circulations may be weaker and more transient, a strong tornado threat persists.

Mesoscale Discussion #2010


The severe weather threat for Tornado Watch 554 continues.


SUMMARY...Tornado potential persists for a mature supercell structure across southwestern Kentucky. A strong tornado remains possible over the next hour or so.


DISCUSSION...A mature, intense supercell with a history of damaging, long-track tornadoes is progressing across southern Kentucky, where the latest mesoanalysis depicts nearly 500 m2/s2 of effective SRH present. The 0640Z OHX VWP also shows nearly 300 m2/s2 of 0-1 km SRH due to a long, curved hodograph driven by a strong LLJ. Mid 60s F surface dewpoints are contributing to 500-1000 J/kg MLCAPE and minimal convective inhibition ahead of the storm, suggesting that tornado potential should continue for at least the next hour. Given the impressive low-level shear and the presence of a 45 kt rotational velocity signature accompanied by a TDS at 0655Z (per KHPX radar), a strong tornado may already be in progress and significant damage may accompany this storm.

Mesoscale Discussion #2014


The severe weather threat for Tornado Watch 561 continues.


SUMMARY...Damaging wind gusts and a tornado or two remain possible across WW 561.


DISCUSSION...A supercell over Marion County Kentucky has shown periods of strong rotation with a tornado debris signature noted over the past 15-30 minutes. Rotation associated with this storm has recently weakened as it continues northeast into eastern portions of the Louisville CWA. This is likely due to weaker low-level instability as surface dewpoints drop off rather quickly from the mid 60s to upper 50s/low 60s. While the cluster of storms over central KY may still produce strong, damaging gusts, the narrowing warm sector downstream may begin to limit stronger tornado potential over the next 1-2 hours.

Mesoscale Discussion #2015


The severe weather threat for Tornado Watch 558 continues.


SUMMARY...A locally higher threat for damaging gusts and tornadoes exists with a supercell structure embedded within the line as it approaches the Nashville metropolitan area.


DISCUSSION...A relatively dominant supercell structure embedded within a north-south oriented segment of the squall line has exhibited strong low-level rotation, with TDSs noted around 0830Z and 0845Z. This storm is progressing in an environment characterized by strong low-level shear, with the 0828Z OHX VWP showing a long, curved hodograph and over 350 m2/s2 0-1 km SRH. Given low to mid 60s F dewpoints residing ahead of the storm, the potential for severe wind gusts and tornadoes is expected to continue over the next hour or so, when the storm is expected to traverse the Nashville Metropolitan area.

Mesoscale Discussion #2027


Concerning...Severe potential...Tornado Watch likely 


Valid 151828Z - 152030Z


Probability of Watch Issuance...95 percent


SUMMARY...Storms are expected to develop and rapidly intensify as they race northeastward this afternoon. Widespread severe winds of 60-75 mph are likely, with gusts to 80-100 mph possible. A few tornadoes, including the potential for a strong tornado or two, may also occur. Tornado Watch issuance is likely by 2 PM CDT.


DISCUSSION...A compact and intense shortwave trough evident on water vapor satellite imagery over the central High Plains will eject quickly northeastward across KS/NE this afternoon, reaching the upper MS Valley by this evening. A strong low-level mass response is occurring ahead of this feature, with surface pressure falls generally ranging from 3 to 5.5 mb per 2 hours based on latest observations across western/central KS/NE. Meanwhile, over eastern KS/NE into much of MO/IA, low-level moisture continues to rapidly advect northward in tandem with a pronounced, 50+ kt south-southwesterly low-level jet. Surface dewpoints have generally increased into the mid 50s to low 60s across this region. As the pronounced large-scale ascent associated with the shortwave trough overspreads the warm sector, the sharp low-level inversion noted on the 18Z sounding from TOP will quickly erode.


Based on linear extrapolation of the band of clouds/showers attendant to the lift with the approaching shortwave trough currently over western KS, convective initiation across parts of central/eastern NE and adjacent northern KS to the east of a surface dryline appears increasingly likely by 20-21Z (2-3 PM CST). These storms are forecast to rapidly strengthen and race northeastward as they encounter at least a weakly unstable airmass and greater low-level moisture with eastward extent over KS/NE. MLCAPE generally ranging from 500-1000 J/kg will be more than sufficient to support surface-based convection.


Very strong flow at both low and mid-levels is expected to overspread the warm sector as the shortwave trough ejects northeastward through this evening. The potential for widespread severe wind of 60-75 mph appears likely, with stronger gusts up to 80-100 mph possible, as these anomalously strong winds aloft reach the surface through mixing and convective downdraft processes. With the deep-layer shear vectors oriented at least partially orthogonal to the surface boundary, some potential for supercells may exist. Given the strength of the low-level shear, a few tornadoes appear likely, and a strong tornado or two may also occur. Otherwise, a broken band of low-topped storms will likely develop as convection shifts into western/central I, southern MN, and vicinity later this afternoon and early evening, with a continued widespread severe/damaging wind threat and potential for a few tornadoes. The rapidly increasing severe risk across this region will warrant Tornado Watch issuance by 20Z (2 PM CST).

Mesoscale Discussion #2029


The severe weather threat for Tornado Watch 563 continues.


SUMMARY...The threat for a few tornadoes and widespread severe winds of 60-85+ mph will spread east-northeastward across parts of eastern Nebraska and northeastern KS through 4 PM CST.


DISCUSSION...A line of storms has quickly developed early this afternoon across portions of north-central KS into south-central NE. Multiple measured wind gusts of 60-85 mph have been recorded across this region as the line moved through. 20Z mesoanalysis shows a narrow corridor of 500-1000 J/kg of MLCAPE preceding the line across northeastern KS into southeastern NE with minimal convective inhibition noted due to the pronounced large-scale ascent preceding a shortwave trough ejecting over the central Plains. A recent VWP from KUEX shows a rapid increase in southwesterly flow in the 0-2 km layer, with winds quickly increasing to around 70-80 kt just 1 km AGL. Potential for these enhanced winds to reach the surface in convective downdrafts will remain high in the short term across northeastern KS and eastern NE as the line races east-northeastward across this area around 50-60 kt. Widespread severe/damaging winds of 60-85 mph will likely be the primary severe threat, with some potential for even higher gusts given the strength of the low-level flow. A few tornadoes with circulations embedded within the line will also be a continued threat with the enhanced low-level shear present (effective SRH around 200-300 m2/s2). A couple of these circulations have already been observed in south-central NE, with at least one CC minimum (likely TDS).

Mesoscale Discussion #2030


The severe weather threat for Tornado Watch 563 continues.


SUMMARY...Widespread damaging winds of 60-85+ mph and the potential for a few tornadoes will spread quickly eastward into western/central Iowa and northwestern Missouri this afternoon.


DISCUSSION...Temperatures ahead of a QLCS across eastern NE and northeastern KS have recently warmed into the mid 60s to mid 70s, with surface dewpoints generally in the mid 50s to low 60s. This squall line is expected to remain well organized in the short term given 60-70+ kt of effective bulk shear present across the warm sector. Strong low/mid-level flow attendant to an ejecting shortwave trough will continue to reach the surface through convective downdraft accelerations. Numerous severe wind gusts of 60-85 mph have been observed at multiple surface sites over the past hour or so across northeastern KS and eastern NE. Potential exists for even stronger gusts given 60-70 kt of flow present around 850 mb. Indeed, a recent wind gust to 93 mph was reported at KLNK (Lincoln, NE) as the line moved through. Widespread severe/damaging winds ar expected to remain prominent as this line of storms races quickly east-northeastward into western/central IA, northwestern MO, and vicinity over the next couple of hours. Multiple embedded mesovorticies have been noted within the line, as low-level shear remains enhanced (effective SRH around 300-400 m2/s2). A few tornadoes will also remain a threat, especially with any embedded supercell within the line, and a strong tornado cannot be ruled out.

Mesoscale Discussion #2032


Concerning...Severe potential...Watch likely 563...


Valid 152251Z - 160045Z


Probability of Watch Issuance...95 percent


SUMMARY...A line of storms will continue to produce significant wind damage, and may also produce several tornadoes as it rapidly moves across Iowa, southern Minnesota and into southwest Wisconsin.


DISCUSSION...A surface low over northwest IA will continue to deepen as it moves northeast into MN this evening. An ongoing line of storms producing significant wind damage along the trailing cold front is expected to remain intact as strong southerly winds warm and destabilize the area downstream. While cool conditions currently exist farther north into MN and WI, models suggest the warm front will mix north, resulting in sufficient SBCAPE to support both wind damage and tornadoes. Effective SRH of 500 m2/s2 is expected which will support rotation regardless of storm mode.

Mesoscale Discussion #2033


The severe weather threat for Severe Thunderstorm Watch 564 continues.


SUMMARY...Widespread damaging winds (including 65+ kt gusts) remain a concern across eastern Kansas into Missouri over the next few hours. A couple of tornadoes also remain possible.


DISCUSSION...An intense squall line has developed across the Mid-Mississippi Valley and is approaching the KS/MO border with a 50 kt forward speed. Several severe wind gusts (some around 65 kts) have been reported over the past hour or so. Given the 60+ kt synoptic-scale 925 mb flow occurring in proximity to the squall, downward momentum transport in the stronger storm cores embedded in the line will continue to support the potential for several additional severe gusts, with at least a few significant severe (65+ kt) gusts expected over the next few hours. Transient supercell structures have also developed within the squall, with up to 400 m2/s2 effective SRH residing ahead of the line, suggesting that a couple of tornadoes could also occur with the more sustained, dominant supercell structures.

Mesoscale Discussion #2034


The severe weather threat for Tornado Watch 563 continues.


SUMMARY...Damage is likely to occur in association with a rapidly moving line of storms across Iowa, northern Missouri, and eventually far southern Minnesota, with a few fast-moving tornadoes possible as well.


DISCUSSION...A particularly damaging line of storms currently extends from a low over northwest IA southward into northwest MO and eastern KS, and is moving east/northeast at 75-85 mph. Several measured sig-severe wind gusts have been measured recently, and this is likely to continue. Further, effective SRH currently ranges from 400-600 m2/s2 across western IA and points south, suggesting brief, but possibly fast-moving embedded QLCS tornadoes are clearly a threat. Destabilization due to the spread of a moist air mass will eventually occur over southern MN behind a diffuse warm front, and tornadoes will be a concern as the low continues to deepen.

Mesoscale Discussion #2036


The severe weather threat for Tornado Watch 565 continues.


SUMMARY...The threat for damaging winds and brief tornadoes continues from Iowa into Wisconsin.


DISCUSSION...A long-lived line of storms with a history of significant wind damage continues to rapidly move eastward at over 70 mph along a cold front. Meanwhile, a warm front is gradually lifting north over far southeast MN and into parts of southwest WI. Forecast soundings from the warm frontal area indicate that a near-60 F surface dewpoint yields 500-750 J/kg MLCAPE. This, combined with effective SRH over 500 m2/s2 suggests that storms will persist across the MN/WI/IA portion of the MS River Valley. Damaging wind gusts remain likely given the speed of this system as well as wind magnitude just off the surface, and low-level shear still supports a QLCS tornado risk.


Farther south across IL and into MO, instability is weaker with more CIN noted on objective analysis. However, the existing line of storms will continue to post a damaging wind risk toward the MS Valley here as well, although the greatest risk remains farther north where the line is oriented perpendicular to the deep-layer shear vector.

Mesoscale Discussion #2038


The severe weather threat for Tornado Watch 565 continues.


SUMMARY...A severe wind risk may eventually push into northern Wisconsin this evening, and a new watch may need to be considered depending on storm trends.


DISCUSSION...The northern end of a long-lived squall line continues to produce severe gusts and damage this evening, moving from southeast MN into western WI. Currently, this section of the line is oriented favorably (more perpendicular) to the winds aloft, aiding storm speed and forward tilt. 


Surface analysis shows that the line is near the warm front, with temperatures cooling back into the mid 50s F northeast of the storms. Very strong southerly winds exist just off the surface, and this is likely aiding elevated instability north of the warm front. 



Given the organization of the line of storms and continued warm advection profiles, some wind threat may persist into north-central or even northern WI this evening. Storm trends are currently being monitored, and a new watch or extension may be needed.

Mesoscale Discussion #2071


Concerning...Severe potential...Watch likely 


Valid 291644Z - 291845Z


Probability of Watch Issuance...95 percent


SUMMARY...The severe thunderstorm threat is expected to increase by 18z. Supercells and bowing segments producing a few tornadoes, damaging gusts and isolated large hail are expected with this activity. A watch is likely by around 18z


DISCUSSION...An area of showers and isolated thunderstorms across parts of northern MS/AL and south-central TN will continue to shift east/northeast through early afternoon in a strong warm advection regime. Airmass recovery in the wake of this activity is evident across parts of northwest MS into southeastern AR where cloud breaks are allowing for greater heating. Temperatures to the west and south of morning precipitation generally are in the low 70s, with upper 60s to low 70s F dewpoints. This is allowing or rather quick destabilization with MLCAPE values quickly increasing to around 500-1000 J/kg. This trend should continue with northeast extent across the MCD area as morning precipitation continues to clear. 


A surface boundary associated with morning convection extends across parts of southeast AR into northern MS/AL and may serve as a focus for greater severe thunderstorms potential by early afternoon. A couple rounds of severe storms may be possible as initial supercell storms develop in the vicinity of this surface boundary within the open warm sector, while additional convection spreads eastward from AR/LA associated with the surface low and cold front. Strong vertical shear, with effective shear magnitudes greater than 50 kt, and a southwesterly low level jet increasing to around 40-50 kt through the day will support supercells. A few tornadoes, one or two of which could be strong, damaging gusts and isolated large hail is expected with this activity. With time, convection may develop into one or more bowing segments closer to the front/surface low. As this occurs, the threat for damaging wind gusts will increase, with a continued threat for mesovortex tornadoes given favorable low level shear and rich boundary-layer moisture. A watch will likely be needed by around 18z.

Mesoscale Discussion #2073


The severe weather threat for Tornado Watch 569 continues.


SUMMARY...The severe thunderstorms threat is expected to increase over the next couple of hours across northern MS.


DISCUSSION...GOES-16 1-minute data, specifically the cloud phase distinction RGB, has shown vertical development in TCU with beginnings of glaciation from near the Mississippi River in far northeast LA into north-central MS over the past 30 minutes. Should this trend continue and semi-discrete cells develop, a corridor of greater relative severe threat can be expected over the next 2-3 hours across the MCD area. 


A surface boundary from morning convection extends from near Tunica, eastward across northern MS. To the south of this boundary, temperatures have warmed into the upper 70s  with dewpoints in the upper 60s to near 70 F. This has resulted in rather quick destabilization with MLCAPE ranging from 500-1500 J/kg. Recent VWP data from KGWX shows a vertically veering wind profile with a somewhat small, but favorably curved low-level hodograph. Low-level shear is forecast to improve somewhat with time, resulting in slightly larger hodographs and a more favorable environment to support supercells capable of producing a few tornadoes this afternoon.