Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Jul 22 2025 19:55:22 ACUS01 KWNS 221955 SWODY1 SPC AC 221953 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0253 PM CDT Tue Jul 22 2025 Valid 222000Z - 231200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS PARTS OF THE NORTHERN PLAINS INTO THE UPPER MISSISSIPPI VALLEY... ....SUMMARY... Scattered severe thunderstorms will be possible over parts of the northern Plains into the upper Mississippi Valley this afternoon into tonight. ....20z Update... Minor updates were made to the D1 Convective Outlook to reduce the Marginal Risk area across North Dakota into northern Minnesota where the front has shifted southward with influence from morning convection. Otherwise, the Slight Risk across the northern Plains into the upper Midwest remains on track. There continues to remain some uncertainty on what the corridor for greater wind risk will be this evening. Cloud cover remains across much of the Slight Risk area. It is mostly clear across southern South Dakota into Wyoming, where temperatures are warming. Thunderstorm activity has begun across the high terrain in Montana and Wyoming. See the previous discussion below for more information. ...Thornton.. 07/22/2025 ..PREV DISCUSSION... /ISSUED 1130 AM CDT Tue Jul 22 2025/ ....Northern Plains into the Upper Mississippi Valley... Visible-satellite imagery late this morning shows extensive cloud debris and convective outflow from ongoing and early morning shower/thunderstorm activity. A composite outflow/front is draped from the ND/MN Red River Valley west-southwestward into northwest SD, with another frontal segment extending into northern WY. Weak to neutral height rises across the northern Plains this afternoon will likely not support a northward oscillation of the boundary into southwest ND. A belt of moderate to strong southwesterly 500-mb flow overhead the north-central Rockies and adjacent plains will be downstream of a larger-scale trough pivoting east across the northern Rockies through tonight. In agreement with earlier forecast thinking, it appears probable that diurnal storms will favor the general area of northern WY/southern MT. This region will generally be post-frontal, but steep mid-level lapse rates and a modestly moist low-level airmass should still aid in the development of at least weak instability. Strong deep-layer shear should support supercells initially, with associated threat for large to perhaps isolated very large hail. Some potential should exist for this convection to grow upscale this evening across parts of the Dakotas and pose a greater threat for severe/damaging winds overnight. But, uncertainty remains high regarding the placement of this possible cluster, and whether it will remain surface-based or elevated. Farther east into the upper MS Valley, it appears less likely that robust convection will develop before this evening due to the stabilizing influence of the ongoing morning activity. If thunderstorms can develop later, most short-term guidance continues to suggest that sufficient airmass recovery will occur to support severe convection with mainly a hail/wind threat. Some diurnal hail/wind threat may develop across IA in association with the lower MO Valley MCV. Uncertainty remains high regarding this scenario. ....Central High Plains... Scattered to numerous high-based thunderstorms should develop this afternoon along/near the surface lee trough extending southward across the central High Plains. While low/mid-level flow and deep-layer shear are all expected to remain weak today across this region due to closer proximity to the upper ridge, heating will contribute to the development of steep 0-3 km lapse rates. Severe gusts will be the primary hazard. ....Southeast... A weak cold front will shift southward today across parts of GA/SC. A rather moist low-level airmass will be in place ahead of the front, with daytime heating encouraging the development of moderate to locally strong instability through the afternoon. Scattered thunderstorms that develop along/ahead of the front, and along various sea breeze circulations, may be capable of producing occasional damaging winds, even though shear will remain weak. $$ = = = 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) .