2019

Mesoscale Discussion #0141


Probability of Watch Issuance...95 percent


SUMMARY...The initial signs of discrete convective development are occurring late this morning in the warm sector.  Rapid environmental changes are forecast to occur between 10am CST/11am EST and the mid afternoon.


DISCUSSION...Visible satellite imagery shows widespread cloud cover across the destabilizing warm sector to the south of the primary frontal zone where the surface low is forecast to develop eastward across central AL into north-central GA later today.  Surface dewpoints over the FL Panhandle and far southern AL have risen around 3 degrees F in the past hour and are indicative of strong poleward moisture advection occurring as the surface cyclone develops. The warming/moistening are contributing to MLCAPE increasing from near 0 J/kg to upwards of 1000-1500 J/kg by early-mid afternoon.  


Late morning VAD data show around 35-45 kt southwesterly 700mb flow from KMOB/KBMX/KMXX/KEOX in central and southern AL but stronger flow (50-55 kt) is now being observed farther west in Jackson, MS(KDGX) and Slidell, LA (KLIX).  Models show the flow intensifying further over AL and GA this afternoon (55-60 kt 700mb).  The end result is a hodograph exhibiting little weakness (no veer-back-veer tendency or a weak layer of winds).  In summary, as moderate buoyancy and strong/veering flow through the profile combine with moist low levels, the threat for strong low-level mesocyclone associated with the discrete storms will increase, along with corresponding risk for tornadoes of which a few may be strong.

Mesoscale Discussion #0145


The severe weather threat for Tornado Watch 7 continues.


SUMMARY...Strong tornado potential appears to be maximizing over east-central AL through 3pm CST.


DISCUSSION...A mature supercell located near Montgomery is favorably located within a region of maximized surface pressure falls (3-4mb per 2 hours) immediately east/southeast of the surface low. KMXX VAD shows 500 m2/s2 0-1km SRH when accounting for the observed Montgomery County supercell's storm motion.  Given the ample buoyancy and intense shear profile in place, it appears tornadogenesis will likely occur within the next 30-60 minutes with the possibility of a strong tornado occurring.

Mesoscale Discussion #0147


The severe weather threat for Tornado Watch 7, 8 continues.


SUMMARY...The potential for tornadoes is seemingly most favorable with storms near and east of the surface low and as storms move within the warm frontal zone where pressure falls are maximized.


DISCUSSION...Latest subjective surface analysis places a 1007mb surface low over central AL with a warm front extending east into central GA near Macon.  Surface pressure falls range from 4-5mb per 2 hours across the warm frontal zone.  Surface temperatures on the immediate cool side of the boundary range are in the middle-upper 60s degrees F but are in the 70-72 degree F range south of the boundary.  It appears the lack of tornado production so far has been limited by modest low-level lapse rates (not quite warm enough boundary layer) and its influence on low-level updraft acceleration with moderate to strong mid-level mesocyclones.  


It remains unclear whether the bootstrapping process for tornadogenesis with existing supercells will occur as the storms move through the warm frontal zone or if an additional forcing mechanism (i.e., squall line cold pool, increasingly favorable large-scale support owing to more juxtaposition with the surface low) is required. Nonetheless, a tornado and and isolated damaging gusts will continue to be hazards associated with the stronger storms.

Mesoscale Discussion #0148


The severe weather threat for Tornado Watch 7, 8 continues.


SUMMARY...An intense tornado with experimental tornado guidance suggestive of wind speeds 125-175 mph based on recent volume scans of rotational velocity and the significant tornado parameter.


DISCUSSION...A very intense supercell tornado will continue to move through a very favorable environment.  Confidence is high for a significant tornado based on rotational velocity continuity, the favorable mesoscale environment, and a relatively unimpeded warm sector along the warm front.

Mesoscale Discussion #0150


The severe weather threat for Tornado Watch 8 continues.


SUMMARY...Tornadic storms with potential tornadic wind speeds 100-140mph are possible with the Twiggs County supercell.


DISCUSSION...KFFC radar imagery indicates rotational velocity values between 45-60 kt with an environment supportive of tornadic supercells. Experimental tornado damage intensity guidance is suggestive of wind speeds between 100-140mph.  Downstream of this storm, expecting little to no storm-scale interference in the near term in a strong low-level shear environment.  As other storms over south-central GA move north into the warm frontal zone over central GA, the tornado potential will probably increase.

Mesoscale Discussion #0144


The severe weather threat for Tornado Watch 8, 9 continues.


SUMMARY...Significant tornado potential appears greatest in the vicinity of the warm frontal zone across central GA during the next 2-3 hours.  The tornado risk will likely increase near the GA/SC border coincident with the intense supercells over central GA moving into the Savannah River Valley.


DISCUSSION...Radar mosaic shows numerous warm sector supercells across southern and central GA.  Surface analysis indicates a 1006mb low near Columbus, GA with a nearly stationary warm frontal zone extending east from the low to 15 mi south of Augusta.  Tornado potential appears to maximize in central GA with the ongoing mature supercells with experimental tornado guidance (conditional on a tornado) indicating damage intensities associated with likely wind speeds in the 80-140mph range with the storm moving from Taylor into Macon County as of 2125z.


Farther east over east-central GA into adjacent portions of SC, model guidance shows a substantial strengthening of flow in the 850-700mb layer between 4pm EST and 7pm EST over the eastern GA/SC region.  Coincident with the strengthening flow fields will be the supercell activity moving into the region from the west.  As such the risk for tornadoes will accompany this activity in the warm sector ahead of the surface low expected to develop to near Augusta by 7pm EST.

Mesoscale Discussion #0322


Probability of Watch Issuance...60 percent


SUMMARY...Thunderstorms are expected to continue to initiate across the region through the afternoon.  Some of these may be accompanied by a risk for severe hail through mid afternoon, before the potential for tornadoes increases closer to 3-4 PM CDT, when the issuance of a watch currently appears most likely.


DISCUSSION...Vigorous thunderstorm development, largely supported by strengthening low-level warm advection above/to the cool side of a northward advancing surface front, is now underway as far east as the Monroe LA vicinity, where a 4-5 mb 2 hour surface pressure fall maximum has spread within the last hour.  In the presence of moderately large CAPE and strong cloud-bearing layer shear, this activity may continue to pose a severe hail risk through mid afternoon.


Gradually, as the front progresses northward, it appears that a warming and moistening boundary layer (including surface dew points increasing to near 70f) may become supportive of intensifying boundary-layer based storm development closer to the 21-22Z time. Models suggest that this will also coincide with enlarging low-level hodographs beneath an 850 mb jet strengthening to 50+ kt, which is expected to support increasing potential for tornadoes, a few of which may become strong.

Mesoscale Discussion #0323


The severe weather threat for Tornado Watch 53 continues.


SUMMARY...Severe weather potential, including the risk for tornadoes, is expected to continue to gradually increase through 3-4 PM CDT.  One or two strong tornadoes is possible.


DISCUSSION...Peak measured (3-second mean wind) winds along the eastward advancing gust front have generally been on the order of 40-45 kts, generally focused along the warm frontal zone.  It appears that the apex of the bowing reflectivity structure and leading edge of outflow will reach the Sabine Valley around 20Z.


Downstream, discrete supercell development continues immediately ahead of the gust front, near/just north of the warm front, with additional discrete storms also beginning to initiate in the warm sector, inland of the coast, near/north of Houston into southwestern Louisiana.  50+ kt south-southwesterly deep layer mean flow will support northward motion of developing warm sector cells across a rapidly destabilizing boundary layer air mass, roughly along a zone Lufkin TX eastward into the Alexandria LA vicinity (near the current position of the warm front), during the next few hours.  This is where near surface hodographs appear largest and the environment most supportive of tornadic potential through 20-21Z.

Mesoscale Discussion #0325


The severe weather threat for Tornado Watch 53, 54 continues.


SUMMARY...Severe weather potential continues to gradually ramp up. This appears likely to include a few supercells with increasing potential for a strong tornadoes through 5-6 PM CDT.


DISCUSSION...Gust front continues to advance eastward around 40 kt, into the Sabine Valley and upper Texas coast, accompanied by a narrow broken line of intense convective development.  This activity is preceded by scattered discrete storm development, and an evolving cluster of storms centered around the Monroe LA area.


It appears that severe weather potential, including potentially damaging wind gusts and a risk for tornadoes, will maximize in a corridor near/north of Natchitoches through the Monroe LA area between now and 22-23Z.  


20Z surface observations indicate that rapid strong 2-hour surface pressure falls have become focused across the Monroe LA into Greenville/Vicksburg MS vicinity, where further boundary layer destabilization associated with warming and moistening may support intensifying boundary-layer based thunderstorm development during the next few hours.  Beneath a 50 kt southerly 850 mb jet, large clockwise curved low-level hodographs will support increasing potential for tornadoes.  A couple could be strong.

Mesoscale Discussion #0326


The severe weather threat for Tornado Watch 54 continues.


SUMMARY...The tornado threat will be maximized across eastern Louisiana and portions of southwest Mississippi along the I-20 corridor over the next 1 to 2 hours.


DISCUSSION...21Z surface analysis shows a warm front along the I-20 corridor from Vicksburg to Jackson, MS. Along and south of this boundary is where the tornado threat will be maximized over the next 1 to 2 hours. Very strong (30 to 35 knot) sustained southeasterly surface winds are present across most surface observing stations

south of this warm front. The DGX VWP shows these winds veering and strengthening to around 50 knots around 1.5 to 2 km above the surface which yields 0-1 SRH around 250 to 300 m2/s2. A line-embedded supercell currently moving into Mississippi in southwest Warren county has taken advantage of this streamwise vorticity rich environment with a consistent 50 to 60 knot Vrot over the last 15 to 20 minutes from the KDGX WSR-88D. This storm, and any additional strong updrafts which can develop in this area within the next 1 to 2 hours have the potential to produce significant tornadoes given the low level thermodynamic and kinematic environment.

Mesoscale Discussion #0328


The severe weather threat for Tornado Watch 54 continues.


SUMMARY...A few strong supercells have developed in west central Mississippi. These supercells are expected to continue through the evening with a continued threat of large hail, damaging winds, and tornadoes.


DISCUSSION...A few supercells have developed on or very near the warm front between Vicksburg and Jackson, MS. A 22Z proximity sounding from JAN shows these storms are in an environment with 0-6km shear in excess of 80 knots with mid-level lapse rates between 7.5 and 8 C/km. In addition, RAP mesoanalysis suggests MLCAPE in

this area is around 1500 J/kg. In addition, using current storm speed and motion with the partial 22Z JAN sounding, these storms are in an environment with 0-1 km SRH in excess of 450 m2/s2. Given this extremely favorable environment, these storms are expected to persist into central Mississippi through the evening with the threat for large hail and tornadoes. Storm interference has disrupted the storms low-level mesocyclone organization and seems to have limited the longevity of low-level tornadic circulations up to this point. While the environment will continue to favor significant tornado potential, messy convective mode and storm interference is expected to continue.

Mesoscale Discussion #0483


The severe weather threat for Tornado Watch 111 continues.


SUMMARY...A tornado threat is likely to continue across WW 111 through late this afternoon. Tornadoes, large hail and wind damage will be possible over the next couple of hours. A potential for strong tornadoes will also exist.


DISCUSSION...Latest surface analysis shows a quasi-stationary front across north-central Oklahoma. Tornadic supercells are ongoing to the southeast of the boundary from just north of Tulsa to southeast of Tulsa. Surface dewpoints in the Tulsa area are in the upper 60s and lower 70s F, contributing to moderate instability with MLCAPE values of 2000-2500 J/kg. In addition, the Tulsa WSR-88D VWP shows a looped hodograph with 0-3 km storm relative helicity near 300 m2/s2. This will continue to be favorable for tornadoes with the more dominant supercells. Low-level shear is forecast to strengthen even

more over the next few hours, suggesting a potential for strong tornadoes will exist. The low-level shear also appears favorable for tornadoes across a large area including southwest Missouri and northwest Arkansas. The amount of instability and deep-layer shear will also be favorable for large hail and wind damage with supercells and the more organized multicells.

Mesoscale Discussion #0573


The severe weather threat for Tornado Watch 144 continues.


SUMMARY...Tornadic potential, particularly in discrete supercell storms, appears likely to increase through 5-7 PM CDT across the Texas Panhandle, including the Amarillo metropolitan area. A strong tornado or two is possible.


DISCUSSION...As a closed mid-level low continues to turn east-northeastward into the southern Rockies, the exit region of an associated cyclonic mid/upper jet appears likely to overspread the region through early evening, in the wake of a initial perturbation now migrating into the central High Plains.  Strengthening upper divergence will enhance ongoing thunderstorm development, which should continue to intensify in the presence of moderate boundary layer instability (CAPE in excess of 2000 J/kg) and strong deep layer shear.


20Z surface data indicate 2-hourly surface pressure falls are in the process of strengthening across much of the south central High Plains, including the Texas Panhandle region.  As low-level wind fields continue to respond, enlarging low-level hodographs are expected to become increasingly conducive to potential for tornadoes through 22-00Z, particularly in association with any continuing or new supercell development.

Mesoscale Discussion #0576


The severe weather threat for Tornado Watch 144 continues.


SUMMARY...Continued storm intensification and new development is expected over the next few hours. All severe weather hazards are expected including large hail (some very large), damaging winds, and tornadoes (some strong).


DISCUSSION...Numerous storms have developed in the Texas and Oklahoma Panhandles with many reports of large hail up to this point. Radar trends and surface observations suggest a large cold pool has started to develop northwest of Amarillo. This is likely the beginning of the cold pool which will eventually move eastward across the Texas panhandle with an increasing damaging wind threat through the evening.


The storms with the greatest hail and tornado potential will be south and east of this outflow boundary where moderate to strong buoyancy and strong deep layer shear exists. This improving shear profile can be seen between the 17Z and 21Z AMA RAOB where effective shear increased from 39 knots to 50 knots and 0-1km SRH increased from 45 m2/s2 to 140 m2/s2. This increasing shear is expected to continue to improve through the evening as mid-level winds increase, surface winds back, and the low-level jet strengthens.


Given this improving shear profile, the tornado threat is expected to increase substantially through the evening. This will especially be the case for storms which remain discrete ahead of the eventual squall line. Currently the storm with the highest tornado potential is likely the mature supercell in Swisher county, Texas. This storm is discrete and expected to remain so for awhile. In addition, the isallobaric response of the low-level wind field has backed surface winds substantially in the vicinity of this storm in the last 2 hours. Additional discrete supercells may also develop in this environment (evidenced by storms currently developing in the eastern Texas panhandle). Any storms in this environment will pose a threat for tornadoes, some potentially significant.

Mesoscale Discussion #0661


The severe weather threat for Tornado Watch 176 continues.


SUMMARY...Significant tornado likely ongoing -- now crossing the Ford/Edwards county line in Kansas.


DISCUSSION...Latest radar data reveals a very strong low-level circulation just east of the Dodge City WSR-88D -- with rotational velocity in excess of 80 kt in some recent volume scans.  This rotational velocity, within the existing high CAPE/high shear environment (resulting in a SIGTOR value of 5-6 across the area) is suggestive of a potentially strong to violent tornado.  With this storm having a history of cyclic tornado occurrence, persons across Edwards county and northeast into parts of Pawnee and Stafford counties may be affected in the next half hour, as the storm moves northeastward at 35 kt.

Mesoscale Discussion #0698


Probability of Watch Issuance...95 percent


SUMMARY...A tornado watch will likely be needed by 1pm CDT.  Storm initiation is expected as early as 1-2pm along the dryline.


DISCUSSION...Visible satellite imagery shows the initial stages of a bubbling cumulus field across the Texas South Plains from near Midland northward to Lubbock.  Late morning surface observations show south-southeasterlies with rapid moisture advection occurring with dewpoints rising to near 70 degrees F near the Low Rolling Plains.  Despite the scattered low cloud cover, additional heating and moistening will contribute to extreme buoyancy (4000-5000 J/kg MLCAPE) developing by early-mid afternoon east of a sharping dryline in parts of northwest and west TX.  The aforementioned theta-e increase and weak large-scale forcing will likely lead to storms explosively developing during the 1pm-3pm period.  


Strong and veering low-level winds beneath very strong deep-layer wind fields will likely result in sickle-shaped hodographs over the TX Panhandle and western OK this afternoon.  0-1km SRH around 250 m2/s2 coupled with the extreme buoyancy will favor long-track and potentially violent tornadoes with the strongest storms.  Giant hail(3-4+ inches in diameter) will be possible.


Farther south, tornadoes and very large hail are possible with any supercells that develop near the Permian Basin.


Mesoscale Discussion #0699


Probability of Watch Issuance...95 percent


SUMMARY...A Particularly Dangerous Situation Tornado Watch will likely be needed for portions of central and western OK. Observational trends and short-term model guidance suggest a watch being issued during the 1pm-2pm period.


DISCUSSION...Visible satellite imagery shows a bubbling cumulus field over western north-central TX into southwest and south-central OK.  Rapid moisture advection is occurring late this morning with surface dewpoints rising into the lower 70s over southern OK. Upwards of 4000 J/kg MLCAPE is expected by early to mid afternoon across western and central OK with intensifying wind profiles.  


Short-term model guidance appears to have a reasonable depiction of free warm sector initiation occurring over southwest and south-central OK during the 2-3pm period.  The observational trend in visible satellite imagery showing more pronounced bands of low cloud cover ---perhaps indicative of horizontal convective rolls and/or low-level confluence zones is supportive evidence for this

model-based depiction.  The expectation is for storms to develop on the northern half of these cloud features with explosive supercell development likely thereafter. Forecast soundings show a very rare combination of intense low-level SRH, very moist boundary, and extreme buoyancy.  As such, the risk for strong to violent tornadoes appears to be increasing later this afternoon into the early evening.

Mesoscale Discussion #0702


Probability of Watch Issuance...95 percent


SUMMARY...Environmental signals are continuing to point towards a tornado outbreak with multiple strong to potentially violent tornadoes across portions of western and central OK later this afternoon into the evening.


DISCUSSION...Visible imagery shows a bubbling and destabilizing boundary layer with upwards of 4000-4500 J/kg MLCAPE developing across the warm sector over western and central OK.  Surface dewpoints are rising through the lower 70s degrees F across western and central OK.


The 18z Fort Worth, TX upper air balloon showed a capping inversion located just below 700mb.  Recent runs of the RAP model show this inversion less pronounced farther north.  Despite temperatures warming into the lower 80s over north TX into southwest OK, this capping inversion has delayed convective initiation.  This is concerning for 2 reasons:  1) the wind profile continues to strengthen across southwest and central OK with the Norman, OK upper air balloon sampling 50kt flow around 850mb which is about 1-2 hours earlier than forecast soundings were showing. 2) It does not appear many storms will develop across southwest OK and resulting in destructive storm-to-storm interference.  In other words, tornadic potential appears very high.  Storms will likely initiate on the north-end of the cloud streets over southwestern OK in the hotter air and intensify and move northeast towards the I-40 and I-35 corridors later.


As such, the very rare combination of shear/buoyancy with many hours of run-to-run consistency of the HRRR model showing discrete supercells all point to a tornado outbreak developing later this afternoon featuring strong to violent long-track tornadoes.


Mesoscale Discussion #0703


The severe weather threat for Tornado Watch 197 continues.


SUMMARY...Rapid development of tornadic supercells expected in the next 1-2 hours.


DISCUSSION...Convective initiation is underway across the Texas Panhandle and west Texas within an environment characterized by MLCAPE of 3500-4000 J/kg, effective bulk shear of 50-60 kt, and effective SRH of 300+ m^2/s^2. In addition, observed soundings launched by the TORUS field program in this area (Wellington, TX) indicate weak CIN and a favorable low-level kinematic environment for tornadoes in proximity to the developing convection, with a sickle-shaped hodograph and 0-1 km AGL SRH near 300 m^2/s^2. Convection that is developing now is expected to mature quickly, and given the ambient environment, storms should quickly evolve into supercell structures capable of significant, long-tracked tornadoes within the next hour or two -- in agreement with SPC objective analysis.

Mesoscale Discussion #0705


The severe weather threat for Tornado Watch 199 continues.


SUMMARY...Tornado potential will likely increase across southwest OK during the next few hours.


DISCUSSION...Radar mosaic shows several quasi-discrete supercells over the eastern TX Panhandle into the Low Rolling Plains. Additional storm development is possible over southwest OK ahead of the supercells located to the west.  It is less clear regarding convective initiation and supercell development farther east towards the I-44/I-35 corridors (besides the Logan County supercell).


Surface analysis shows lower 70s surface dewpoints with temperatures ranging from the lower 80s over southwest OK to the middle 70s near OKC.  A composite front/outflow-reinforced boundary is located across the eastern TX Panhandle arcing to the east-northeast to near Stillwater, OK.  South of this boundary, a very unstable to extremely unstable airmass will support intense updraft development with existing storms.  KTLX VAD data shows a larger hodograph compared to KFDR's VAD (0-1km SRH of 300 and 200 m2/s2, respectively).


Short-term model guidance has trended away from a possible scenario of discrete storm development over south-central OK.  The most probable scenario involves several tornadic supercells likely moving across southwest OK and approaching the I-40 corridor west of the OKC metro.

Mesoscale Discussion #0709


The severe weather threat for Tornado Watch 199 continues.


SUMMARY...The severe threat continues across WW 199.  A volatile environment remains in place across the discussion area with all modes of severe (including significant tornadoes) remaining possible.


DISCUSSION...In the short term, tornado potential appears to be maximized in a couple of areas - one over Greer County, OK (where recent radar trends indicate potential for significant tornadoes and very large hail) and near Noble/Payne Counties in OK where a forward-propagating linear segment may interact with an outflow/warm frontal boundary immediately downstream of that region. Surface-based storms continue in a very volatile shear/instability combination, with all modes of severe remaining possible (including significant tornadoes).  Shear will only increase in response to significant strengthening of low-level flow through the evening.


A convectively modified surface boundary continues to migrate slowly southward across west-central Oklahoma and resides along a line from near PNC to just south of CSM and westward to south of AMA.  Storms north of this boundary will be elevated, but capable of large hail. If the current storm near Greer County, OK can continue on the warm side of the boundary, it will continue with a risk of occasional strong to violent tornadogenesis in addition to large hail and damaging wind gusts.

Mesoscale Discussion #0715


The severe weather threat for Tornado Watch 200 continues.


SUMMARY...Significant tornado potential exists with a storm in Delaware County, Oklahoma.


DISCUSSION...A supercell initially over Mayes/Cherokee Counties in Oklahoma favorably interacted with an outflow boundary and generated an intense mesocyclone, with experimental guidance suggestive of a significant tornado in the area.  Strong rotation continues on radar, and significant tornado potential will exist with this storm as it migrates east-northeastward through Delaware County, OK; Benton County, AR; and McDonald County, MO through 05Z as long as it can remain rooted near the outflow boundary.

Mesoscale Discussion #0729


The severe weather threat for Tornado Watch 207 continues.


SUMMARY...Potential significant tornado entering western portions of the St. Louis Metro area.


DISCUSSION...A linear segment has interacted favorably with a warm-frontal zone located west-to-east through parts of the St. Louis Metro area.  This storm is moving northeast around 50 knots, and experimental guidance suggests continued potential for a significant tornado in the region.  This storm should continue migrating northeastward through the western and northern portions of St. Louis Metro area over the next hour or so.

Mesoscale Discussion #0734


Probability of Watch Issuance...95 percent


SUMMARY...Supercells capable of large hail, damaging winds, and tornadoes -- a few of which may be strong -- are expected. A tornado watch is likely.


DISCUSSION...Visible satellite shows boundary layer cumulus developing over portions of northeast Oklahoma, southeast Kansas, northwest Arkansas, and southwest Missouri, as low-level moisture advects northward across the region. Surface dew points in the low 70s F are overspreading the region, ahead of a stalled cold front. Along the front, elevated convection has developed and is moving parallel to the boundary. With continued diabatic heating and low-level moisture advection, further destabilization can be expected, with MLCAPE values of 3000-4000 J/kg developing by late afternoon. 


Given these thermodynamic conditions, convective initiation is expected within the next 1-2 hours. Convection along the front may eventually root into the boundary layer, and additional storms may develop in the warm sector, particularly in southern parts of the MCD area. As storms develop, effective bulk shear of 50-55 kt will help organize the convection into supercell structures. With effective SRH exceeding 200 m^2/s^2, tornadoes -- a few of which could be strong -- are possible, along with the threat for large hail and damaging winds. A tornado watch will likely be issued within the next hour.

Mesoscale Discussion #0736


The severe weather threat for Tornado Watch 212 continues.


SUMMARY...Potential for a strong tornado or two appears likely to increase near and south through east of Tulsa between now and 6-8 PM CDT.


DISCUSSION...Discrete supercell development is ongoing, particularly near the Okmulgee and Stillwater areas.  This is occurring in the presence of rather strong (90-120 m) 12 hour 500 mb height rises, and it remains at least somewhat unclear what impact this will have on subsequent development.  However, activity is being aided by large-scale forcing for ascent associated with warm advection, and appears generally north of stronger mid-level inhibition associated with warmer elevated mixed-layer air (as inferred by 700 mb temps around +10 C to the south and southwest).


Cells now approaching Okmulgee appear increasingly rooted in the boundary layer, which is characterized by mixed-layer CAPE approaching 4000 J/kg.  Embedded within strongly sheared southwesterly deep layer mean ambient flow on the order of 40 kt, there appears considerable potential for further intensification and progression into at least southern/eastern portions of the Greater Tulsa metropolitan area through 23-01Z.  Models suggest that this will coincide with strengthening of southerly 850 mb flow to around 40 kt, with enlarging clockwise curved low-level hodographs becoming supportive of continuing/increasing tornadic potential.

Mesoscale Discussion #0740


The severe weather threat for Tornado Watch 212 continues.


SUMMARY...Risk for a strong tornado or two will continue, mainly near the Interstate 44 corridor of northeast Oklahoma through 8-10 PM. A transition to primarily a severe hail/wind risk is expected to gradually occur across the Missouri Ozarks and lower Missouri Valley by late evening.


DISCUSSION...Vigorous thunderstorm development now progressing northeast of the Tulsa area remains generally

discrete/supercellular.  In the presence of lingering large boundary layer CAPE, strong deep layer vertical shear and enlarging low-level hodographs, there still appears potential for a strong tornado to form near the Interstate 44 corridor of northeast Oklahoma through 01-03Z.


Otherwise, thunderstorm activity, including a few embedded

supercells, has become increasingly numerous along a line northeast and east of Bartlesville OK through areas north/east of Sedalia MO. This is focused along a cold frontal zone, which is forecast to slowly advance eastward across the lower Missouri Valley and Missouri Ozarks vicinity through late evening.  A gradual consolidation of storms is expected to take place in response to lift associated with warm advection, with perhaps a tendency for convection to become undercut by the front.  As this occurs, the primary severe hazard probably will transition to severe hail with potential for strong convective gusts to increase.

Mesoscale Discussion #0742


The severe weather threat for Tornado Watch 213 continues.


SUMMARY...An increase in storm coverage has occurred in Tornado Watch 213 with the strongest activity entering southwestern portions of the watch area. A few intense supercells will bring a greater threat for tornadoes as they move northeast. Severe hail and damaging wind gusts will also remain possible.


DISCUSSION...Storm coverage has been on the increase in WW 213 as supercells from west-central Missouri propagate into the watch area. Two supercells within Randolph and Howard Counties in Missouri have had a history of strong mid-level rotation and a confirmed tornado near Cairo, MO. As they progress to the northeast, the will enter and environment with strong effective SRH on the order of 300 m2/s2. Low-level SRH shear has been steadily increasing over the last hour per KLSX radar and with at least modest increase in the low-level jet, this trend should continue for the next hour or two. Given these trends, the referenced storms should pose the greatest threat for a tornado into the mid evening. Deeper into the evening, the

cold front to the northwest of this activity will begin to push to the southwest, undercutting any remaining discrete storms and reducing the tornado threat. Observed 00Z soundings within the region still show 7-7.5 C/km lapse rates which will bring a threat for large hail until storms become more linear.

Mesoscale Discussion #0804


The severe weather threat for Severe Thunderstorm Watch 245, 247 continues.


SUMMARY...Severe gusts and mesovortices may continue to northeast in the vicinity of the I-40 and I-44 corridors during the next 1-2 hours.  A local extension-in-area for severe thunderstorm watch 247 may be needed in the short term.


DISCUSSION...Radar imagery during the past 30 minutes has shown a couple of brief circulations embedded near the apex of a bowing segment across the greater OKC metro.  An outflow boundary intersection with the bow likely contributed to a tornadic circulation over Canadian County during the past hour.  KTLX VAD has strengthened during the past 2 hours with 0-1km shear approaching 40kt.  Given the moist/unstable airmass in place with a mature small-scale bow echo, a continued risk for severe gusts/wind damage and perhaps brief mesovortices seems probable during the next 1-2 hours.


**Note: This MCD preceded the  El Reno EF3 QLCS Spin-Up

Mesoscale Discussion #0840


The severe weather threat for Tornado Watch 263, 266 continues.


SUMMARY...Severe thunderstorms posing a risk for tornadoes and damaging wind gusts will continue to develop east-southeastward into and across portions of western and central Ohio, including the Interstate 70 corridor from Dayton to Columbus, through 10-11 PM EDT.


DISCUSSION...Aside from a few strong convective gusts evident in recent surface observations across north central Indiana (including 49 kt at Grissum AFB), there is little yet evident in latest (00Z) surface analysis indicating strengthening of a surface cold pool. Discrete supercell development persists ahead of a narrow evolving line of storms, which appears to trail south of an MCV now progressing eastward near the Michigan/Indiana border.


It still appears that thunderstorms will continue to gradually consolidate along the warm front east of Muncie IN into areas northwest of Dayton OH through the 10-11 PM EDT time frame, accompanied by increasing potential for damaging wind gusts. However, this may continue to be preceded by discrete supercellular development accompanied by the risk for tornadoes.

Mesoscale Discussion #0842


The severe weather threat for Tornado Watch 266 continues.


SUMMARY...The risk for supercells capable of producing tornadoes continues, and may persist at least another couple of hours, into the Midnight to 2 AM EDT time frame, across and south of the Interstate 70 corridor of Ohio.  Trends are being monitored for the possibility of an additional Tornado Watch to the southeast of Tornado Watch 266.


DISCUSSION...The ongoing cluster of severe thunderstorms has failed to produce substantive convective outflow, and strongest storms have remained generally discrete in nature with a number of supercells continuing to develop and track east-southeastward across the Interstate 70 corridor roughly between Dayton and Columbus. This includes one cell which has likely produced a strong tornado across the Dayton Metropolitan area.  


It is possible that recent activity has been augmented by at least some strengthening of the west-southwesterly 850 mb jet, atop the decoupling boundary layer to the warm side of the front. However, it remains unclear how much longer this will persist, with boundary layer instability to the warm side of the front gradually waning with the loss of daytime heating.  And models suggest supporting

lift associated with low-level warm advection may tend to shift more eastward than southeastward across the remainder of central/southern Ohio through 05-06z.  However, in the near term, large clockwise curved low-level hodographs will maintain a continuing risk for tornadoes with the stronger supercells as they progress south of Interstate 70.

Mesoscale Discussion #0863


The severe weather threat for Tornado Watch 275 continues.


SUMMARY...Strong thunderstorm activity will continue to gradually increase during the next few hours.  This may include a few supercells, with potential for tornadoes increasing toward 7-8 PM, particularly north/northeast of the Kansas City metropolitan area.


DISCUSSION...Intense thunderstorm development near Emporia northward into the Topeka area, as well as well as along and north of a stalled outflow boundary, from St. Joseph east-northeastward through the Missouri/Iowa border vicinity, is generally focused within a zone of strong warm advection on the nose of the plume of capping elevated-mixed layer air.  This is generally beneath the region of focused strong upper-level divergence (around 250 mb), which is aiding large-scale ascent that appears likely to gradually spread east-northeastward through this evening.


This lift, coupled with inflow of seasonably high boundary layer moisture content characterized by moderate CAPE (on the order of 2000+ J/kg), is expected to contribute to considerable further upscale convective growth through 7-8 PM. In the presence of strongly sheared, 40+ kt southwesterly deep layer mean ambient flow, this probably will include a few supercells. Except in the immediate vicinity of the outflow boundary, north of both the Kansas

City metro and Topeka areas, low-level shear remains relatively modest.  However, at least some further strengthening of southerly 850 mb flow (in excess of 30 kt) will contribute to enlarging low-level hodographs toward sunset.  This may support an increasing risk for tornadoes, particularly where outflow generated by the current Emporia/Topeka convection intersects the stalled outflow boundary, probably north/northeast of Kansas City Mo.

Mesoscale Discussion #1533


The severe weather threat for Severe Thunderstorm Watch 525 continues.


SUMMARY...Intense winds expected across Menominee, Oconto and Marinette Counties over the next 30-60 minutes. Severe threat will continue across broader northern/central WI this evening.


DISCUSSION...An intense bow echo continues to shift east/southeast across northern/central WI this evening. While measured severe wind gusts have been few, many wind damage reports have been received this evening. Additionally, radar observations suggest that several corridors of intense winds are occurring as the bow evolves. Most recently, a corridor of intense wind is expected to move across Langlade County toward Menominee, Oconto and Marinette Counties over the next 30-60 minutes. This is evident in the intense bow surging across Langlade County with a very sharp reflectivity gradient shown from the Green Bay 88-D. Additionally, radar velocities have increased to 80-90 kt at around 5 kft. This is the most intense and well defined evidence of a descending rear inflow jet so far this evening. Expect intense wind threat to continue across WW 525.

Mesoscale Discussion #2091


The severe weather threat for Tornado Watch 676 continues.


SUMMARY...Tornado is currently ongoing across northern Dallas County. The environment is supportive of a strong tornado, with additional tornadoes possible downstream in the next hour or so.


DISCUSSION...Recent radar signatures from KFWS reveal an intense supercell characterized by a 0.5 degree rotational velocity between 60 and 65 kt. A tornadic debris signature has also been noted on recent radar scans. This signature is occurring in an environment characterized by STP between 3 and 4. Previous signatures within similar environments produced damage-estimated wind speeds from 120 to 160 mph and a confidence is high for an intense tornado.

Mesoscale Discussion #2202


Probability of Watch Issuance...80 percent


SUMMARY...Storm strength and persistence will continue to gradually increase of the next few hours. Supercells capable of damaging wind gusts, tornadoes, and isolated hail are possible and a Tornado Watch will likely be needed by 18z.


DISCUSSION...Air mass from southeast TX across LA and into MS continues to destabilize amidst modest moisture advection. Recent surface analysis reveals 70 deg F dewpoints across southeast TX and southwest LA and mid-60 deg F dewpoints now near the LA/AR border. 12Z soundings from LCH, SHV, and JAN all sampled a seasonally strong EML. Despite favorable low-level moisture, the warm temperatures aloft associated with this EML are likely tempering updraft intensity/persistence thus far. However, continued theta-e advection will likely lead to a gradually decreasing convective inhibition, which will in turn lead to gradually increasing updraft strength and persistence. 


Regional VAD data show long and veering hodographs supportive of supercells, suggesting that once storm updraft strength and persistence increase, there will be an increased likelihood for supercells capable of damaging wind gusts and tornadoes. Some isolated hail is also possible. Wind profiles are strong enough to support strong tornadoes. Convective trends are being monitored

closely and a Tornado Watch will likely be needed across portions LA and western MS (and potentially far southeast TX) before 18Z.

Mesoscale Discussion #2205


The severe weather threat for Tornado Watch 700 continues.


SUMMARY...A corridor favorable for strong tornadoes is developing across central LA.


DISCUSSION...Recent VAD data from KPOE and KLCH continues to show long hodographs (i.e. 0-6 km bulk shear over 50 kt) and vertically veering low-level wind profiles. Surface winds across southern LA have increased slightly but still remain generally 10 to 15 kt from the south. Recent mesoanalysis places a small area of 45 kt 850-mb winds over central LA, matching expectations based on previous model guidance. Instability continues to increase as well, with mesoanalysis suggesting 2000 J/kg MLCAPE now stretching into southwest LA and 1500 J/kg MLCAPE covering much of the central and southern portions of the state.


Low-level winds are expected to strengthen further over the next hour or two, resulting in a favorable overlap between the increased low-level vertical shear and building instability. As a result, a corridor of increased tornado risk appears to be developing across central LA. Additionally, storms have already developed upstream of this area. Given these conditions, storms capable of strong tornadoes are possible.

Mesoscale Discussion #2206


The severe weather threat for Tornado Watch 700 continues.


SUMMARY...Based on recent radar and environmental data, a strong to potentially intense tornado with potential peak winds of 110 to 155 mph (EF1-EF3) is likely ongoing.


DISCUSSION...Recent radar signatures from KPOE and KLCH as of 17:31z reveal an intense supercell characterized by a 0.5-0.9 degree rotational velocity between 61 and 70 kt. A tornadic debris signature has also been noted on recent radar scans. These signatures are occurring in an environment characterized by STP between 4 and 5. Previous signatures within similar environments produced tornado-damage-estimated wind speeds from 110 to 155 mph and confidence is high for likely strong to potentially intense tornado. A tornado is ongoing and may continue based on the rotational velocity continuity and the storm moving within a favorable downstream environment.

Mesoscale Discussion #2207


The severe weather threat for Tornado Watch 700 continues.


SUMMARY...Based on recent radar and environmental data, a strong to potentially intense tornado with potential peak winds of 110 to 155 mph (EF1-EF3) is likely ongoing and tracking towards Alexandria, LA.


DISCUSSION...Recent radar signatures from KPOE as of 1832z reveal a long track tornadic supercell characterized by a 0.5 degree rotational velocity between 61 and 70 kt. A tornadic debris signature has also been noted on recent radar scans. These signatures are occurring in an environment characterized by STP between 4 and 5. Previous signatures within similar environments produced tornado-damage-estimated wind speeds from 110 to 155 mph and confidence is high for likely strong to potentially intense tornado. A tornado is ongoing and may continue based on the rotational velocity continuity and the storm moving within a favorable downstream environment.

Mesoscale Discussion #2208


The severe weather threat for Tornado Watch 700 continues.


SUMMARY...Air mass across east-central LA and southwest MS remains supportive of all severe hazards, including strong tornadoes.


DISCUSSION...Recent KPOE VAD sampled 50 kt winds between 1 and 2 kft and surface winds across far southwest MS and adjacent east-central LA have slightly increased. These increases have result in a slight strengthening of the deep-layer shear as well as storm-relative helicity across the region. In contrast to these kinematic increases, this air mass over the region is slightly cooler (i.e. temperatures in mid 70s) and less moist (i.e. dewpoints in the mid to upper 60s). Even so, the air mass downstream of the ongoing storm near Alexandria, LA as well as those in Avoyelles and St. Landry Parishes remains supportive of supercells capable of all severe hazards, including strong tornadoes.

Mesoscale Discussion #2211


The severe weather threat for Tornado Watch 700 continues.


SUMMARY...Greatest threat for tornadoes will be across southern Mississippi over the next hour. Significant tornadoes are possible.


DISCUSSION...Multiple supercells are moving northeast across southwest Mississippi with confirmed tornado reports with two of the storms. Radar signatures are indicative of possible strong tornadoes with VROT values of 35-45 knots and tornadic debris signatures were sampled per KDGX in the last 10-20 minutes. The environment remains conducive for tornadic supercells with significant tornadoes possible with 0-1 km SRH of 200+ and STP values around 3.

Mesoscale Discussion #2213


The severe weather threat for Tornado Watch 701 continues.


SUMMARY...Tornado potential will likely maximize during the next 1-2 hours. A strong tornado is possible with the supercells moving northeast across the US 49 corridor.


DISCUSSION...Radar imagery shows a cluster of supercells over southern MS moving northeast within a moderately unstable airmass. Surface conditions show middle 70s degrees temperatures and dewpoints in the 68-70 degrees F range.  RAP forecast sounding show strengthening and veering winds with height with minimal weakness (i.e., veer-back-veer).  As a result, hodographs seem most favorable within this corridor over southern MS. Additionally, the maximizing of buoyancy across southern MS translates to a heightened supercell-tornado risk potentially evolving during the next 1-2 hours.

Mesoscale Discussion #2216


The severe weather threat for Tornado Watch 702 continues.


SUMMARY...A corridor for enhanced tornado potential will extend in the near term across southeast MS with a discrete supercell. The risk may continue into far west-central AL between 730-800pm CST.


DISCUSSION...Radar imagery shows a discrete supercell over Jones County, MS with a messy supercell structure straddling Smith/Jasper counties as of 610pm CST.  The low-level airmass is gradually moistening along the MS/AL border with surface dewpoints immediately downstream of the supercells slowly rising into the upper 60s degrees F.  The observed 00z Slidell, LA sounding showed 1600 J/kg MLCAPE and a 15 g/kg lowest 100mb mean mixing ratio. Farther north ahead of the aforementioned storms, RAP forecast soundings show enlarged low-level hodographs with around 300-350 m2/s^2 0-1km SRH and around 1000 J/kg MLCAPE.  The greater risk for a tornado or series of tornadoes will likely accompany the discrete cell during the next 1-2 hours.

Mesoscale Discussion #2217


The severe weather threat for Tornado Watch 701 continues.


SUMMARY...Based on recent radar and environmental data, a strong to potentially intense tornado with potential peak winds of 120 to 155 mph (EF2-EF3) is likely ongoing. This storm has a history of producing tornadoes.


DISCUSSION...An intense supercell will continue to move through a favorable environment over southeast Mississippi, characterized by 0-1 km SRH around 300 m2/s2 and MLCAPE near 1200 J/kg per recent mesoanalysis. Recent radar signatures from KDGX as of 0017 UTC reveal an intense supercell characterized by a 0.3 degree rotational velocity between 55 and 60 kt. A tornadic debris signature has also been noted on recent radar scans. These signatures are occurring in an environment characterized by STP between 3 and 4. Previous signatures within similar environments produced tornado-damage-estimated wind speeds from 120 to 155 mph and confidence is high for likely strong to potentially intense tornado. A tornado is ongoing and may continue based on the rotational

velocity continuity and the storm moving within a favorable downstream environment.