Subj : DAY3SVR: Nws Storm Prediction Center Norman Ok To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Jul 21 2025 07:31:03 ACUS03 KWNS 210730 SWODY3 SPC AC 210729 Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0229 AM CDT Mon Jul 21 2025 Valid 231200Z - 241200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS WEDNESDAY INTO WEDNESDAY NIGHT ACROSS PARTS OF EAST CENTRAL MINNESOTA...NORTHERN AND CENTRAL WISCONSIN AND UPPER MICHIGAN... ....SUMMARY... One or two organizing clusters of storms posing a risk for severe wind and perhaps some hail are possible across parts of the Upper Midwest into adjacent Great Lakes region Wednesday through Wednesday night. ....Discussion... Models indicate some further suppression of the northeastern Pacific mid-level ridging, with flow becoming more zonal and progressive across the British Columbia coast into the Canadian Prairies during this period. A lingering short wave perturbation emerging from the northern U.S. intermountain region may accelerate east of the Montana Rockies, along the central Canadian/U.S. border. This appears likely to be preceded by more subtle smaller-scale impulses migrating around the northern periphery of persistent mid-level ridging centered over the Ohio Valley. It appears that these will accelerate into the southern fringe of strengthening mid-level westerly flow across parts of the Upper Midwest/Great Lakes region into Ontario and Quebec, between the mid-level ridge and a significant mid-level trough/cyclone migrating slowly across Hudson Bay. While a cold front trailing the surface cyclone may continue to advance southward through the Great Plains to the lee of the Rockies, models suggest that it probably will stall across parts of the Upper Midwest into adjacent Great Lakes Wednesday into Wednesday night, near the northern periphery of the mid-level ridge. ....Upper Midwest/Great Lakes... It appears that a seasonably moist boundary layer (including dew points around or above 70F) advecting into the region during the day Wednesday, if not earlier, will become supportive of moderate to strong potential instability beneath a remnant plume of modestly steep lower/mid-tropospheric lapse rates. Models suggest that this will generally focus along the stalling surface front, where 30-40 kt west-southwesterly flow in the 700-500 mb layer will contribute to the possible evolution of organizing, eastward propagating convective systems with the potential to produce strong to severe surface gusts. There appears a general signal within the model output that a stalling, trailing flank of outflow associated with an initial cluster of storms may become a focus for renewed convective development, near where it intersects the front, just ahead of an eastward migrating frontal wave, across northern Wisconsin into Upper Michigan during the peak late afternoon into evening instability. ....Lee of northern Rockies into Front Range... In the presence of steep lapse rates, moistening easterly to southeasterly near-surface flow, beneath modest westerly flow aloft, may contribute to sufficient destabilization and shear to support widely scattered strong to severe storms. This may include evolving supercells near/just east of the higher terrain late Wednesday afternoon and evening. ...Kerr.. 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) .