Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Feb 26 2023 13:01:14 ACUS01 KWNS 261301 SWODY1 SPC AC 261259 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0659 AM CST Sun Feb 26 2023 Valid 261300Z - 271200Z ....THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF OKLAHOMA AND NORTHWEST TEXAS... ....SUMMARY... An extensive swath of severe thunderstorm winds, some exceeding 75 mph, is expected this evening into tonight from the eastern Texas Panhandle across parts of Oklahoma to the western Ozarks region. A few tornadoes also are possible, with potential for significant/EF2+ damage. ....Synopsis... A series of well-developed shortwave perturbations moving over the West Coast States will be the greatest mid/upper-level influences on convective potential this period. One trough will move ashore in the Pacific Northwest and northern CA through the remainder of the morning, as another upstream trough digs southeastward out of the Gulf of Alaska region. The latter should be approaching the West Coast by 12Z tomorrow. The combined effects of those troughs will contribute to eastward ejection/acceleration of a compact, pronounced cyclone -- initially evident in moisture-channel imagery over southern parts of NV/CA and northern Baja. The 500-mb low and its accompanying, intense shortwave trough will move east-northeastward today, reaching eastern parts of CO and NM by 00Z. By 12Z, the low should reach northern MO, with the trough becoming negatively tilted and extending toward the Mid-South region. The 11Z surface chart showed a wavy warm/marine frontal zone across southern LA and southeast/south-central TX, bending southward over northeastern Coahuila and Nuevo Leon. This boundary should become more diffuse through the day amidst increasing boundary-layer southerlies on both sides. A diffusion/extension of the 60 F isodrosotherm north of this boundary already was evident into the southern Hill Country/Edwards Plateau area around JCT-SOA. During the 18-21Z period, rapid surface cyclogenesis will occur in an area of current lee troughing over eastern CO. The low will shift into northwestern KS, with combined lee trough and Pacific cold front southward through the eastern Panhandles and then southwestward over the Permian Basin and far west TX. At that time, the front should be catching up to an antecedent dryline that will develop through the previous daylight hours near the Caprock, south-southwestward across the lowest Pecos Valley area. The low will deepen as it sweeps quickly east-northeastward toward IA overnight, and the cold front overtakes the remainder of the dryline. By 12Z, the front should extend from the low across western IL, southeastern MO, central AR, and parts of east and south TX. ....Southern Plains to Ozarks region... Thunderstorms should form quickly late this afternoon, in a north/south-aligned belt from parts of southwestern KS across the eastern Panhandles of TX/OK. This activity should include a few supercells with damaging gusts, large hail and tornado potential. Over southern parts of the corridor, supercell maturation and movement into relatively maximized low-level moisture (with very large hodographs) will promote the greatest tornado potential. During the evening, a severe line of thunderstorms should sweep east-northeastward over OK and KS, offering localized gusts above 75 mph and widespread damaging wind. Some backbuilding into northwest/ north-central TX is possible, though the southern extent and intensity will be limited by weaker deep-layer forcing and stronger capping than areas near and north of the Red River. A narrow corridor of "just in time" favorable moisture return is expected over the eastern Panhandles/western OK and northwest TX corridor, just ahead of the dryline and cold front. This should occur in trajectories emanating from near the marine/warm frontal zone now near I-10. Surface dewpoints mainly in the 50s F, with a couple hours of some mid/late-afternoon cloud breaks and heating, should underlie steep midlevel lapse rates, with MLCAPE around 1000-1500 J/kg reaching the Red River and perhaps the I-40 area of western OK/eastern TX Panhandle. Buoyancy will diminish northward from there, but with at least briefly surface-based inflow parcels into southwestern/south-central KS as well. The mass response to the fast-moving, compact mid/upper trough will lead to a preceding swath of intense winds throughout most of the troposphere. This will include strongly difluent, rapidly strengthening mid/upper-level flow over the southern Plains late this afternoon into this evening, accompanied by a rapid-onset swath of strong DCVA/ascent and nearly collocated frontal lift. Related upscale growth of the convection into an organized complex is expected near the western OK/TX Panhandle line, with organization further improving eastward into OK. This should lead to a well- developed, aggregate downdraft slab with scattered hurricane-force surface wind speeds where the near-surface layer is not too stable. At least isolated significant-gust potential may extend well into the Ozarks tonight, even as the complex outruns the narrow/foregoing corridor of optimally favorable boundary-layer air and into greater stability. Regionally rare vertical shear is forecast, with effective-shear magnitudes of 55-75 kt. Very fast storm motions of 50-60 kt (Interstate highway speeds) are likely, both for early-stage supercells and elements within the subsequent convective complex, based on the forecast deep-layer and mean-wind fields. These extreme storm motions essentially make severe any part of a downdraft whose surface translation keeps up with that of the cell above. Such forward speeds also impart substantially greater vector flow into the right (south) side of any tornadoes that form, increasing significant damage potential there. This all is probable wherever boundary-layer lapse rates are large enough to maintain effectively surface-based parcels, which should reach well past the I-35 corridor over northern and perhaps central OK. The 60-70-kt western fringes of the LLJ will contribute to very large hodographs in the immediate preconvective sector, with effective SRH exceeding 500 J/kg and 1/2-km SRH over 300 J/kg in some areas. This should help to maintain tornado potential well past the transition to quasi-linear mode. ...Edwards/Kerr.. 02/26/2023 $$ = = = To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .