Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Sep 21 2025 06:02:34 ACUS01 KWNS 210602 SWODY1 SPC AC 210600 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0100 AM CDT Sun Sep 21 2025 Valid 211200Z - 221200Z ....THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR PARTS OF THE SOUTHERN PLAINS INTO THE OZARKS...MID MS VALLEY...OH VALLEY...AND SOUTHERN GREAT LAKES...AND ALSO FROM NORTHEAST NE/SOUTHEAST SD INTO SOUTHERN MN/NORTHERN IA... ....SUMMARY... Isolated severe thunderstorms are possible later today across parts of the southern Plains into the Ozarks, mid Mississippi Valley, Ohio Valley, and southern Great Lakes. A few strong to severe thunderstorms are also possible from the mid Missouri Valley into southern Minnesota and northern Iowa. ....Synopsis... A broad mid/upper-level trough will cover much of the central/eastern CONUS later today, with several embedded vorticity maxima expected to move across parts of the Great Plains into the Midwest and Ohio Valley. Modest midlevel flow atop a sufficiently moist and unstable environment will support some potential for strong to locally severe storms across a relatively large area. Localized corridors of somewhat greater severe threat may evolve where deep-layer shear is enhanced by one of the embedded midlevel shortwaves, as well as where midlevel flow veers to west-northwesterly across parts of the mid MO Valley and southern Plains. ....Parts of TX into southern OK... Extensive overnight convection is expected to leave a residual outflow boundary that will be located somewhere in the vicinity of north TX/southern OK by afternoon. While some midlevel warming is expected across the southern Plains through the day, relatively strong heating, and the potential influence of an MCV that may evolve from overnight convection, will support isolated to widely scattered storm development this afternoon/evening near the outflow boundary, and potentially southward along a diffuse dryline into northwest/west-central TX. Moderate buoyancy and 35-50 kt of effective shear within the northwesterly flow regime across parts of north TX into southern OK will conditionally support splitting supercells capable of producing hail and localized severe gusts. There is some uncertainty regarding the placement of the boundary by afternoon and the magnitude of any MCV-related enhancement to deep-layer shear and storm coverage, but greater probabilities may be needed if confidence increases in development of multiple supercells and/or an organized cluster within this regime. ....Northeast NE/southeast SD into southern MN/northern IA... A compact mid/upper-level low will move southeastward from eastern ND into MN later today. This low and the attendant shortwave trough will aid in the development of isolated to widely scattered storms by late afternoon or early evening from southwest MN into adjacent southeast SD, northeast NE, and northwest IA, in the vicinity of a weak surface boundary. Relatively cool temperatures aloft, moderate buoyancy, and effective shear of 25-35 kt will support strong multicells and perhaps a couple splitting supercells. Large hail is expected to the primary hazard, though localized strong gusts will also be possible with the strongest storms. ....Eastern KS into MO... A cluster of elevated convection will likely be ongoing at the start of the period across central/eastern KS. This cluster and possibly an attendant MCV may encounter an environment across parts of MO that is recovering from a separate area of overnight convection near the Ozarks. While background midlevel flow will only support effective shear of 20-25 kt, any MCV-related enhancement to the flow would result in sufficient deep-layer shear for somewhat more organized storms. If sufficient destabilization can occur, then a few modestly organized cells or clusters may evolve this afternoon and evening, accompanied by a threat for localized damaging wind and perhaps some hail. ....Parts of the Ohio Valley and Great Lakes... Modest deep-layer southwesterly flow will overspread parts of the southern Great Lakes and Ohio Valley later today, in advance of the midlevel shortwave trough moving across the upper MS Valley. Scattered thunderstorm development is expected across the region, within a moderately unstable and weakly capped environment. Midlevel lapse rates and deep-layer shear are expected to remain relatively weak, but steepening low-level lapse rates will result in potential for cells/clusters capable of locally damaging wind this afternoon into the early evening. There is also some potential for a storm cluster or loosely organized MCS to develop across the lower MO/mid MS Valley and move toward parts of the southern Great Lakes later tonight. ...Dean/Halbert.. 09/21/2025 $$ = = = 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 3.28-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .