Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Jul 21 2025 16:34:27 ACUS01 KWNS 211633 SWODY1 SPC AC 211632 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1132 AM CDT Mon Jul 21 2025 Valid 211630Z - 221200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE NORTHERN PLAINS... ....SUMMARY... Severe thunderstorms capable of producing large hail, severe gusts, and perhaps a tornado or two will be possible late this afternoon into tonight across parts of the northern Plains. ....Northern Plains into the Upper Midwest... Water-vapor imagery shows a mid-level trough progressing eastward across the Pacific Northwest towards the northern Rockies. A lead mid-level vorticity max rotating through the base of the trough is forecast to pivot east-northeastward from north-central ID into MT by the early evening. In the low levels, a stationary frontal zone extends from near the NE/SD border west-northwestward to near the ID/WY/MT border with an easterly component to the low-level flow being maintained across eastern into central portions of MT. A moisture plume protrudes northwestward along and north of this boundary with a reservoir of 70s F dewpoints over NE to lower 60s in southeast MT (850-mb dewpoints around 16 deg C per objective analysis). A notable capping inversion will likely inhibit storm development until mid afternoon and the initial storm activity will likely focus near higher terrain and over southern MT. Steep mid-level lapse rates and 30-45 kt southwesterly 500-mb flow will support supercells with large to very large hail accompanying these storms from near the Black Hills into southern MT. A tornado risk may develop where locally backed flow in the presence of smaller temperature-dewpoint spreads could evolve near the boundary. Upscale growth into one or more clusters or an MCS seems plausible this evening into the overnight as storms move/develop east into the Dakotas. ....Central Plains... No change was made to the previous forecast for the Central Plains region. Much of the central Plains will remain capped today, as the upper ridge and warm temperatures aloft exert their influence. A surface trough is expected to extend southward across the central High Plains this afternoon, and a remnant MCV related to earlier convection should move eastward along/near the NE/KS border. Both of these features may aid in at least isolated thunderstorm development this afternoon, in the presence of moderate to strong instability amid modest deep-layer shear. Isolated severe hail and wind gusts may occur with any of the more robust cores that can develop and be maintained in an otherwise weak forcing regime. ....Tennessee Valley into the Southeast... Midday visible-satellite imagery shows an agitated cumulus field from southern GA northwestward into the southern Appalachians and Cumberland Plateau. 12 UTC raobs from Jacksonville, Atlanta, and Charleston showed PW in excess of 2 inches, signifying a very moist, deep troposphere. Surface temperatures will continue to warm into the 90s F, thereby steepening 0-2 km lapse rates. As storms develop, some of the stronger water-loaded downdrafts may yield a threat for localized 50-65 mph gusts and pockets of wind damage. This activity will likely diminish by the evening. ...Smith/Halbert.. 07/21/2025 $$ = = = 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) .