Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Sep 28 2023 12:34:08 ACUS01 KWNS 281234 SWODY1 SPC AC 281232 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0732 AM CDT Thu Sep 28 2023 Valid 281300Z - 291200Z ....NO SEVERE THUNDERSTORM AREAS FORECAST... ....SUMMARY... The risk for severe thunderstorms appears negligible (less than 5 percent) across the U.S. today through tonight. ....Discussion... Models indicate that lingering mid-level ridging, southeast of Hudson Bay into the St. Lawrence Valley, will break down today, as an initially vigorous short wave trough within the westerlies accelerates northeast of the Saskatchewan/Montana border vicinity toward Hudson Bay. This lead perturbation, emerging from larger-scale troughing developing inland of the Pacific coast, appears likely to continue to weaken, but it may still support modest surface cyclogenesis across Manitoba. An initial trailing cold front likely will stall across the Dakotas into the Great Basin, as another short wave impulse turns inland along the western Canadian/U.S. border vicinity and a third impulse begins to dig within an amplifying regime offshore of the Pacific coast. Despite deepening surface troughing southward to the lee of the southern Rockies, and strengthening southerly low-level flow to its east, particularly by late this evening across the southern Great Plains into the middle Missouri Valley, a substantive return flow of boundary-layer moisture from the Gulf of Mexico is unlikely. High moisture content air will generally remain confined to areas south of a lingering frontal zone offshore of the south Atlantic coast into the northeastern Gulf of Mexico, and east of a remnant mid-level trough axis across the northeastern through southwestern Gulf of Mexico. Remnant surface ridging, extending to the southwest of a weakening surface high shifting across the New England and Canadian Maritimes vicinity, will maintain a considerable influence across most areas east of the Mississippi Valley into the northwestern Gulf coast. However, weak troughing within the larger-scale ridge remains a focus for relatively moist boundary-layer air, beneath modestly cool mid-levels associated with a weakening mid-level low and troughing to the south of the Great Lakes region. As the blocking pattern continues to break down, the mid-level low and trough are forecast to slowly progress into and across the Appalachians, within a generally weak westerly mean flow. This may lead to elevated moisture return from offshore of the Atlantic coast, weak destabilization and thunderstorm development across parts of the northern Mid Atlantic into southern New England by late tonight, while convective potential diminishes across the Ohio Valley. ....Lower Ohio Valley vicinity... Forcing for ascent and destabilization beneath the mid-level low, and near the weak surface trough, across the middle Mississippi into lower Ohio Valleys, has been supportive of only a few, mostly marginally severe storms the past few days. Although thunderstorm development may persist today with continuing moist inflow into a lingering warm advection regime across southeast Missouri into the southwestern Kentucky/northwestern Tennessee vicinity, slowly rising mid-level heights/warming aloft and weakening flow in the 850-700 mb layer seem likely to contribute to increasingly negligible risk for severe weather. ...Kerr.. 09/28/2023 $$ = = = 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) .