Subj : DAY3SVR: Nws Storm Prediction Center Norman Ok To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue May 13 2025 07:29:45 ACUS03 KWNS 130729 SWODY3 SPC AC 130729 Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0229 AM CDT Tue May 13 2025 Valid 151200Z - 161200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS PARTS OF THE UPPER MISSISSIPPI RIVER VALLEY AND WESTERN GREAT LAKES... ....SUMMARY... Scattered strong to severe thunderstorms are expected across parts of the western Great Lakes and Midwest Thursday afternoon and evening. A more isolated/conditional severe threat will extend into the mid-Mississippi River Valley during the late evening and overnight hours. ....Synopsis... The upper trough currently situated over the Pacific Northwest is forecast to eject into the Plains/upper MS River Valley through the day Thursday. A surface low will intensify through early afternoon before beginning the occlusion process as a Pacific cold front pushes east. Ahead of this front, southeasterly low-level flow will advect upper 50s to mid 60s dewpoints northeastward into the upper MS River Valley and Midwest regions. Thunderstorm development is likely along the front as it impinges on the returning moisture across the upper MS Valley and western Great Lakes. Strong capping with southward extent will likely result in more isolated thunderstorm development along the front into parts of the Midwest and OH Valley. ....Upper MS Valley into the Western Great Lakes... Thunderstorm development is anticipated by early afternoon across parts of the upper MS River Valley as the Pacific front surges into the region under a 50-60 knot mid-level jet. While higher-quality moisture will likely remain south of the region, dewpoints in the low to mid 60s, coupled with steepening mid-level lapse rates, should support MLCAPE values between 1500-2500 J/kg. Strong mid-level flow will promote supercell wind profiles, and mean storm motions off the front will likely support initially discrete cells that should pose a severe hail/wind threat. Upscale growth into an organized line is possible given strong forcing along the front as an arcing line of storms moves east into the Great Lakes region. Discrete supercells will be most probable on the southern extent of the line of storms, but increasing capping with southwestward extent introduces considerable uncertainty in how far south storms will develop. The best thermodynamic and kinematic environment will likely extend across IN into western OH and southward to the OH river, but most deterministic and ensemble solutions show only weak QPF signals across this region through early evening. 15%/Slight risk probabilities were maintained for IN/western OH due to account for low-probability, but potentially high-impact supercells within this environment, but further refinements are likely as the likelihood of convective initiation becomes more apparent. ....Mid-MS River Valley and lower OH Valley... The Pacific front is forecast to gradually stall across northern AR into the lower OH Valley through the overnight hours as the primary surface low occludes to the north. Thunderstorm development along the front is possible during the late evening/overnight hours with most ensemble solutions showing some QPF signal during the 06-12 UTC period as low-level isentropic ascent increases along the stalled boundary. 40-50 knot mid-level flow will favor organized convection, though storm motions along the boundary may promote clustering with time. Regardless, some severe threat will likely manifest with this activity during the overnight hours into early Friday morning. ...Moore.. 05/13/2025 $$ = = = 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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .