Severe Storm Outlook Narrative (AC)
Issued by NWS
Issued by NWS
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
280 ACUS01 KWNS 251258 SWODY1 SPC AC 251257 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0757 AM CDT Sat May 25 2024 Valid 251300Z - 261200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF KANSAS...OKLAHOMA AND SOUTHWESTERN MISSOURI... ...SUMMARY... An outbreak of severe thunderstorms is possible from late afternoon into tonight over parts of the central and southern Plains. A few long-lived supercells capable of intense tornadoes may occur. Giant hail and destructive wind gusts are also expected. ...Synopsis... In mid/upper levels, a synoptic-scale trough over the western CONUS -- with several associated shortwaves and vorticity lobes -- will shift eastward to the Great Plains States by the end of the period. A positively tilted, basal shortwave trough -- evident in moisture- channel imagery over parts of the lower Colorado River Valley and southern CA -- will eject east-northeastward slightly faster than the progress of the synoptic trough. This shortwave trough should reach southwestern KS, the TX Panhandle, and western/southern NM by 00Z, then extend near an MKC-CSM-HOB line by 12Z tomorrow. Meanwhile, farther poleward, a shortwave trough now apparent over the northwestern NV/eastern OR area should amplify and pivot across the central Rockies, reaching eastern CO by 12Z. A northern-stream shortwave trough now over parts of Lake Superior, Upper MI and WI should move east-northeastward to parts of Lake Huron and southern ON by 00Z, then break through a synoptic ridge to its east. By 12Z, this feature should reach parts of the St. Lawrence Valley and northern New England. Meanwhile, a broad fetch of difluent mid/upper-level flow will persist over the southeastern CONUS, with several embedded, convectively generated/augmented vorticity lobes. The 11Z surface analysis showed a cold front from lower MI southwestward across southern IL and southeastern MO, becoming quasistationary over western AR, southeastern OK, and north-central/ west-central TX. Amid intense low-level mass response to the approaching mid/upper trough, the boundary is forecast to move northward across northwest TX and OK today as a warm front, becoming more diffuse with time into evening as the airmass now to its south approaches (and eventually moves into some of) southern KS. A dryline will develop and sharpen with time across the area from west-central TX northward to western KS, as moist advection continues to its east. An elongated area of low pressure -- attached to a lee trough over eastern CO -- is expected to consolidate today, with the resultant low reaching the MCK vicinity by 00Z. The low should move/redevelop southward into western KS overnight then shift eastward to near SLN by 12Z. To its southwest, frontogenesis will occur overnight, leading to a 12Z cold-frontal position from the low across northwestern OK and parts of the TX Panhandle. ...Central/southern Plains... Isolated to scattered thunderstorms should develop by midafternoon near the low and dryline, from parts of western NE to KS and perhaps over northwest TX and western OK. The airmass ahead of this activity will destabilize, moisten and get more strongly sheared with time, supporting all severe hazards to significant levels (tornadoes, hail, gusts). The activity in NE/KS will occur in less moisture than farther south, with deeper, strongly mixed subcloud layers promoting the possibility of earlier cold-pool development after initial evolution to supercell structures. Relatively dense concentrations of large to very large hail, then severe wind, are possible -- along with potential for a band of thunderstorms to aggregate and sweep eastward toward the lower Missouri Valley tonight. The low-level wind profile for much of the afternoon will support both right- and left-moving supercells (each capable of very large/damaging hail). The tornado threat generally should increase with time from midafternoon into early evening before peaking, especially from about southern KS southward. As the LLJ strengthens from late afternoon into evening, greatly enlarging hodographs, and the richest moisture spreads northward through southern/central OK, the parameter space will become much more suitable for long-lived, significant tornadoes. Meanwhile the threat for large to very large hail and severe downdrafts will continue with any relatively discrete cells. In parts of north TX to central OK, forecast soundings from multiple different models reasonably superimpose MLCAPE of 4000-5000 J/kg, upper 60s to mid 70s F dewpoints, 50-70 kt effective-shear magnitudes, and effective SRH as high as 400-700 J/kg by early evening. That is an uncommon (even for this time of year) environment supporting potentially dangerous supercells, and may spread north of I-40 as far north as southern KS. However, some important caveats remain that preclude any greater unconditional severe probabilities for now. The strongest deep-layer forcing across the central Plains will remaining displaced north of the remnant/diffuse frontal zone, and thus north of the richer moisture over TX and into southern OK, for much of the day and evening. The development of only isolated/few storms in TX may greatly increase the threat in OK. By contrast, dense coverage of afternoon convection over west-central/northwest TX may affect potential farther north -- whether directly through left-split interactions or indirectly via outflow-related theta-e deficits advected northward. Also, a plume of high clouds is forecast to develop and stream east-northeastward for hundreds of miles off the mountains of south-central/southeastern NM as the shortwave trough approaches, potentially limiting diurnal heating/destabilization between about I-40 and southern KS. North and south of that, heating will be stronger, for longer. Still, any supercell(s) that can move through the high-SRH, large-buoyancy environment of north TX to southern KS from late afternoon onward will pose a threat for substantial tornado production. ...Lower Great Lakes/upper Ohio Valley... Widely scattered to scattered thunderstorms are expected to develop near the cold front, and along a nearly parallel, prefrontal trough/convergence zone this afternoon, moving eastward to southeastward across the outlook area and persisting into early evening. Aside from lift along those boundaries, activity will be supported by diurnally weakened MLCINH, with surface dewpoints in the upper 50s to mid 60s F contributing to around 1500 J/kg MLCAPE. Weak low-level flow and nearly unidirectional low/middle-level wind profiles will limit shear, except through the entire cloud layer. Although the shortwave trough will affect very little of this area directly, its flattening of the ridge and related enhancement to mid/upper-level gradient winds will enable strong flow in higher portions of the buoyant layer to aid somewhat in multicell organization. Damaging gusts and isolated hail will be possible from the best-organized convection. ...Southeastern CONUS... Multiple mesoscale boundaries -- both from ongoing convection over the region and from later-developing outflow and differential- heating zones -- will support isolated potential for severe gusts and/or hail today across a broad swath of the Southeast, from the Mid-South to GA and parts of the Carolinas. Separately, a merger of sea breezes over southeastern FL should prompt scattered to widely scattered thunderstorms this afternoon. Both areas will be characterized by rich moisture but generally weak flow in low/middle levels, though locally backed winds on the east and north sides of boundaries may augment vertical shear enough to support occasional supercell structures. MLCAPE should range from around 3000 J/kg across the Mid-South to 1500-2000 J/kg over outlooked parts of AL/GA/FL/Carolinas. Damaging to isolated severe gusts, as well as isolated large hail, will be possible, mainly from afternoon into early evening. Any aggregated thunderstorm clusters in the Carolinas to AL corridor may move southeastward with damaging-gust potential continuing into the evening. ..Edwards/Goss.. 05/25/2024 $$