Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Sep 21 2025 20:01:03 ACUS01 KWNS 212000 SWODY1 SPC AC 211959 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0259 PM CDT Sun Sep 21 2025 Valid 212000Z - 221200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS NORTH TEXAS INTO SOUTHERN OKLAHOMA... ....SUMMARY... Large hail and severe gusts may occur with supercells that develop this afternoon across parts of north Texas and southern Oklahoma. ....20z Update... The previous forecast largely remains on track with only minor modifications outlined below. ....Ozarks... 5% wind probabilities were slightly expanded across northern AR/southeast MO to better align with the expected trajectory of developing upstream convection across northeast OK/northwest AR, which should spread east/northeast through mid-evening based on latest CAM guidance. Loosely organized clusters appear probable, and deep-layer shear should be adequate (around 20-25 knots) for periodic intensification with an attendant threat for strong/severe winds. ....Mid Missouri Valley into Southern Minnesota/Northern Iowa... Severe risk probabilities were trimmed across portions of eastern SD/northeast NE based on latest surface obs/satellite data that shows the best low-level convergence across far eastern SD/far southwest MN. Correspondingly, time-lagged CAM ensemble guidance suggests the highest probability for strong/severe storms will reside mainly across southwest MN/northwest IA this evening. ....Southern Oklahoma/northern Texas... Latest surface analysis reveals multiple boundaries draped across the Red River Valley region to the east of a weak surface low over the Rolling Plains of northwest TX. Lingering convection from this morning near the I-35 corridor has persisted longer than anticipated, which has stunted diurnal heating across portions of the Red River Valley to some degree. It remains unclear exactly which boundary will be most influential for thunderstorm development, which may have implications for storm mode/evolution. However, strong heating to the south of the outflow boundaries combined with glancing ascent from the passing MCV over central OK should still promote at least isolated to scattered convection by mid-evening. ...Moore.. 09/21/2025 ..PREV DISCUSSION... /ISSUED 1121 AM CDT Sun Sep 21 2025/ ....Southern Plains into the Ozarks and Mid Mississippi Valley... Radar mosaic data this morning shows a pair of MCVs moving slowly east over central KS and OK and immediately downstream of an impulse moving east-southeastward (per water-vapor imagery) from the central High Plains towards the lower MO Valley. Considerable cloud cover persists from the Red River northward into the lower MO Valley in association with overnight and morning convection. Surface analysis places an outflow boundary across north TX to the south of ongoing elevated storms near the Red River. Along and to the south of the boundary, rich low-level moisture coupled with heating will lead to moderate destabilization by mid afternoon. The glancing influence of the MCV combined with the low-level convergence along the outflow boundary will probably lead to widely scattered to scattered storms developing by mid-late afternoon over the Red River Valley. Elongated hodographs due to 70-kt northwesterly high-level flow will favor supercellular organization with the stronger updrafts. Large hail and severe gusts appear to be the primary threats with this activity through the early evening before the severe threat likely diminishes after sunset. Farther north, weak mid-level troughing with multiple embedded perturbations will move eastward across the central Plains into the Ozarks and mid MS Valley. Heating will likely be greatest across MO ahead of the aforementioned KS MCV with weak to locally moderate instability this afternoon along/south of a front that should be draped across northern KS/MO. As modest large-scale ascent overspreads the warm sector, at least scattered thunderstorms are forecast to develop this afternoon in a weakly sheared environment, with modest enhancement provided by the eastward-moving MCV across MO. Isolated hail and damaging winds may occur with the stronger cores, with some potential for eventual clustering towards the MS River by early evening. ....Midwest/Great Lakes... A broad zone of modest (20-30 kt) west-southwesterly mid-level flow will be maintained today over much of the Midwest/Great Lakes, on the southeast periphery of weak upper troughing over the Upper Midwest. Diurnal heating of a seasonably moist airmass will lead to isolated to widely scattered storms eventually developing late this afternoon into the evening. Somewhat poor mid-level lapse rates will likely stunt storm intensity, but a few widely spaced damaging gusts cannot be ruled out within this general corridor. This activity should quickly weaken this evening with the loss of heating. ....Mid Missouri Valley into Southern Minnesota/Northern Iowa... A compact mid/upper-level low will continue to migrate eastward across the Upper Midwest through early Monday morning. This low and attendant shortwave trough may aid in the development of isolated to widely scattered storms by early evening from southern MN into northeast NE in the vicinity of a weak surface boundary. Forecast soundings show some modest enhancement to the hodograph by early evening, which may yield a couple of stronger storms. Multicells or transient supercell structures are possible with the strongest cells and an accompanying isolated risk for severe may occur before this activity weakens by late evening. $$ = = = 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) .