Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Aug 13 2025 05:56:01 ACUS01 KWNS 130555 SWODY1 SPC AC 130554 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1254 AM CDT Wed Aug 13 2025 Valid 131200Z - 141200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE CENTRAL PLAINS... ....SUMMARY... The evolution of an organized cluster of thunderstorms accompanied by strong to severe wind gusts appears probable across parts of the central Plains this evening and overnight. Scattered thunderstorms across the Mid-Atlantic/Northeast may produce sporadic damaging winds this afternoon. ....Synopsis... Strong to severe thunderstorm chances today will primarily be focused across the Mid-Atlantic/Northeast and across the central Plains. Early-morning water-vapor imagery depicts a broad upper-level trough across eastern Canada and Great Lakes region with a diffuse surface front draped from the Midwest southwestward into the Plains. This wave and its attendant surface front will spread east through the day, reaching the Mid-Atlantic by around peak heating when conditions should be adequately unstable for thunderstorms. Further west, a deepening upper trough will progress rapidly across the Pacific Northwest and northern Rockies over the next 24 hours. Ascent ahead of this wave overspreading a dry, but buoyant, air mass will promote scattered thunderstorms with robust convection anticipated across the Plains later this evening/overnight as lift impinges on a more moist/buoyant air mass. ....Central Plains... 05 UTC surface observations show modest moisture return ongoing across the Plains in the wake of a recent frontal passage. Through the afternoon, a deepening of the lee trough will promote stronger moisture return just as lift ahead of the approaching wave and high-based convection emanating off the central Rockies spreads east. Deep, well-mixed boundary layers to the west of the surface trough will promote strong to severe downbursts winds as well as outflow dominant storms. Most CAM guidance suggest cold pool consolidation will be adequate for upscale growth of at least one convective cluster across the High Plains by mid/late evening. This activity will likely intensify as it encounters richer moisture within a moderately sheared environment (35-40 knots of effective shear). This scenario appears to be the most probable based on ensemble consensus, and hints that strong to severe winds will likely overspread much of southern SD and northern NE through the overnight hours. While CAMs show reasonably good agreement on the trajectory of this system, the exact corridor of propagation remains uncertain. A few solutions hint at more cellular development across portions of SD after roughly 02 UTC as isentropic ascent over an effective warm frontal zone increases with a strengthening of the nocturnal jet. Cells developing within the warm advection regime may evolve into supercells with an attendant risk for large hail given strong veering between 1-3 km and moderate effective shear. A propagating cluster may emerge out of this regime, but ensemble support for this scenario is comparatively weak. ....Mid-Atlantic/Northeast... 00z soundings across the region sampled rich low-level moisture as well as poor mid-level lapse rates. However, west/southwesterly flow aloft will advect steeper mid-level lapse rates over the next 12-18 hours. The combination of steepening lapse rates and diurnal heating of a moist air mass should result in a modestly buoyant, but weakly capped, environment across the Mid-Atlantic. Focused forcing along the front coupled with limited inhibition should promote scattered to widespread thunderstorms by 19-21 UTC. Damaging downbursts will be possible with this activity - especially where surface temperatures can warm into the upper 80s and low 90s. Based on recent ensemble guidance, this appears most probable from southern PA into the New England region. While deep-layer shear will be fairly weak, very weak surface winds under 20-25 knot mid-level flow may provide adequate deep-layer wind shear for a few persistent, more robust cells and/or clusters. ...Moore/Hart.. 08/13/2025 $$ = = = 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) .