Subj : DAY1SVR: HIGH RISK PLAINS To : All From : Dumas Walker Date : Mon May 06 2024 09:31 am ACUS01 KWNS 061252 SWODY1 SPC AC 061250 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0750 AM CDT Mon May 06 2024 Valid 061300Z - 071200Z ....THERE IS A HIGH RISK OF SEVERE THUNDERSTORMS OVER PARTS OF WESTERN...CENTRAL AND NORTHERN OKLAHOMA TO SOUTH-CENTRAL KANSAS... ....SUMMARY... A regional outbreak of severe weather with multiple strong, long-tracked tornadoes, as well as very large hail and severe thunderstorm gusts, is expected over parts of the south-central Plains from this afternoon through evening. ....Synopsis... In mid/upper levels, a strong synoptic-scale trough was evident in moisture-channel imagery from the northern Rockies, through a low over northeastern UT, then southward to the international border near the AZ/NM line. The main 500-mb low should pivot northeastward toward the Black Hills and deepen by 00Z, with trough northwestward over central MT and southward across eastern parts of CO/NM. A basal shortwave trough -- now from central CO to the Four Corners area -- should swing northeastward then northward, reaching southern SD, western NE and eastern CO by 00Z. This perturbation then should shift northeastward, possibly merging with convectively generated vorticity over NE and SD this evening and tonight, and reaching eastern SD, southwestern MN and IA by 12Z. A weaker, but still influential perturbation -- now over parts of southern NV/northern AZ -- should make a net eastward shift to parts of northeastern NM and the TX Panhandle by 00Z, reaching southern KS and northern OK by 12Z. Associated substantial height falls and DCVA should remain over and north of the Red River Valley through this evening. At the surface, an elongated area of low pressure was analyzed on the 11Z chart over eastern WY, with Pacific cold front across eastern CO and northeastern/north-central NM. A dryline extended from the front over southeastern CO to eastern NM and the TX Trans-Pecos region, and should mix eastward to southwestern KS, eastern OK/TX Panhandles, and west-central/southwest TX by late afternoon. The cold front should overtake the dryline across the central Plains through the afternoon, then over OK overnight. A developing/synoptic warm-frontal zone was apparent from southeastern WY across central KS to southern MO, and should move northeastward to the lower/mid Missouri Valley through the period. The southern warm front -- demarcating the northern rim of a richly moist Gulf airmass from outflow-modified air, was drawn near the Red River from the Arklatex to the southeastern TX Panhandle. This boundary will shift northward through OK and much of KS today while becoming diffuse, and possibly catching up to the northern warm front. ....OK, Southern KS, Red River region... Thunderstorms are expected to develop by mid/late afternoon along and ahead of the dryline, near the eastern TX Panhandle/western OK line or 100W longitude into southern KS, then strengthen quickly to severe levels as they move eastward. Given the already very favorable parameter space by late afternoon, and increasingly so into early/mid evening, the concern is high for at least a few cyclic, tornadic supercells producing multiple significant tornadoes along potentially long paths. The threat for such tornadoes, as well as very large/destructive hail, will be maintained well into the late evening, and may even increase as hodographs further enlarge beneath the LLJ. Some uncertainty lingers as to how many such supercells will track across the outlook area, but given the unusually favorable environment and increasing confidence, a "high risk" outlook is warranted for areas between roughly the I-40 corridor in OK and the US-54/500 corridor in southern KS. Compared to farther north in KS, the environment will feature slightly stronger CINH, very rich low-level moisture (dewpoints commonly upper 60s to low 70s F), lack of frontal forcing (mainly dryline instead), and more orthogonal mean-wind/deep-shear vectors relative to the boundary. The 12Z FWD sounding sampled the richly moist and deep boundary layer that will be shifting northward across OK today, with mean mixing ratio of 15 g/kg. As low clouds erode in the moist sector from west-east, diabatic heating will boost MLCAPE into the 2500-4000 J/kg range over western/central OK and southern/ central KS, and contribute to greater potential for discrete supercells to develop and last a few hours before potential major upscale evolution to lines or clusters this evening. Hodographs will be favorable for tornadoes soon after initiation, and enlarge further ahead of the activity with time. Effective SRH commonly around 200-300 J/kg is expected late this afternoon and 300-500 J/kg after 00Z, amidst strengthening LLJ and deep shear (effective-shear magnitudes reaching 45-60 kt). Effective-layer STP in the 5-12 range may be realized for a few hours this evening across parts of OK and southern KS. Stronger MLCINH and weaker large-scale support will contribute to lesser storm coverage with southward extent over southern OK, though significant tornadoes and damaging hail may be possible from any that form. The corridor of favorable buoyancy will enlarge eastward this evening with continued moisture transport/advection, helping to maintain surface-based effective-inflow parcels well eastward into the Ozarks and vicinity to maintain eventual upscale growth, possibly linking with the southern part of QLCS activity sweeping across the Missouri Valley region. ....Central Plains... Thunderstorms should develop as early as midday to early afternoon over portions of western KS and southwestern NE, where CINH will be weakest, as the southern part of the front overtakes the dryline and impinges on a rapidly destabilizing/moistening sector to the east. Initial supercell mode is possible, with tornadoes (some strong), large to very large hail and damaging gusts all possible. With time this afternoon into evening, a more quasi-linear storm mode may evolve as the influence of frontal forcing increases, versus some component of flow across the boundary. As that occurs, tornadoes still will be possible, and the hail threat will transition to severe wind with eastward extent. Some significant (near 75 mph or higher) gusts will be possible as the momentum of stronger flow aloft gets transported to the surface, with increasing forced ascent along the leading edge of the complex. 60s F surface dewpoints will overspread a northward-narrowing sector across much of KS and NE today, contributing to peak/preconvective MLCAPE increasing into the 2000-3000 J/kg range, as deep shear strengthens, and hodographs extend, while maintaining favorable curvature. ....Northern Plains... From central NE northwestward, the prefrontal corridor of favorable moisture and diurnal destabilization will become quite narrow. Nonetheless, it should support scattered thunderstorms in northward- shifting plume, curving from the western Dakotas (and perhaps parts of extreme northeastern WY and southeastern MT) southeastward to central NE, and connecting to the northern part of the central Plains severe threat. With strong large-scale lift, cooling aloft, rapidly weakening MLCINH, and robust low-level mass response/shear expected ahead of the ejecting shortwave trough, confidence is growing that an arc of strong-severe thunderstorms will develop, offering large hail, severe gusts and at least marginal tornado potential. Even with 50s to low 60s F surface dewpoints and limited time for substantial diabatic heating, the net steepening of low/ middle level lapse rates should support peak MLCAPE near or slightly above 1000 J/kg. Deep shear may not be particularly intense in a regime of strongly difluent flow aloft, but still should be adequate for supercell potential given large lowest-km hodographs possible, and effective SRH in the 150-300 J/kg range. Severe potential should diminish after about 00Z. ....West-central/southwest TX... Isolated thunderstorms are possible in mid/late afternoon along/ ahead of the dryline over northwest to southwest TX. Although large-scale/mid-upper forcing will be negligible, any pockets of relatively persistent/maximized low-level lift associated with solenoidal processes on the dryline may persist enough to initiate convection. Mid/upper 60s to low 70s F surface dewpoints and steep low/middle-level lapse rates will contribute to 3000-4000 J/kg MLCAPE amidst enough deep shear for supercells. A conditional significant-hail and marginal tornado threat exists with sustained supercell(s) -- if any can form. Coverage concerns preclude more than marginal categorical outlook at this time. ...Edwards/Broyles.. 05/06/2024 $$ --- SBBSecho 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (21:1/175) .