Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Aug 16 2025 19:59:06 ACUS01 KWNS 161958 SWODY1 SPC AC 161957 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0257 PM CDT Sat Aug 16 2025 Valid 162000Z - 171200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS EVENING AND TONIGHT OVER PART OF SD...AND THIS AFTERNOON THROUGH TONIGHT OVER SOUTHEAST MN...SOUTHERN WI...AND NORTHERN IL... ....SUMMARY... Scattered strong/severe thunderstorms are possible today into tonight across parts of the northern Great Plains into the Midwest and Great Lakes regions. ....20Z Update... The prior forecast reasoning remains valid. Severe probabilities were reduced in parts of northern/central Wisconsin where prior convection has stabilized the boundary layer. Elsewhere, only minor changes were made to the general thunderstorm forecast based on current observational trends. See the previous discussion as well as MCDs 1965/1966 for additional information. ...Wendt.. 08/16/2025 ..PREV DISCUSSION... /ISSUED 1130 AM CDT Sat Aug 16 2025/ ....Upper Midwest into the Mid MS Valley and Upper Great Lakes Region... An expansive MCS continues to move eastward across the Upper Midwest, with a well-defined MCV evident in radar imagery over the central WI/MN border vicinity. This MCS has continued to gradually weaken throughout the morning, but a few strong updrafts persist along its southeastern periphery over central WI. This portion of the MCS is on the far northeastern periphery of the plume of steeper mid-level lapse rates that extends from the northern/central High Plains across the central Plains and into the Mid MS Valley. This plume is observable in the 12Z sounding from DVN and ILX, which sampled 700-500 mb lapse rates of 7.8 and 7.2 deg C per km, respectively. Dewpoints downstream across southern WI, northern IL, and northern IN are in the low 70s, with upper 60s dewpoints also covering much of southern Lower MI. The combination of ample low-level moisture and steep mid-level lapse rates will result in strong to very strong buoyancy to the south of the MCS from the MN/IA border into northern/central IL. Given the lack of a well-defined surface boundary and negligible large-scale ascent, additional thunderstorm development will be associated with outflow from with the MCS, which results in greater-than-average uncertainty for the Day 1 period. Ample moisture and buoyancy downstream of the leading edge of the MCS suggests the greater severe potential this afternoon/evening will likely be associated with redevelopment/reintensification of the MCS. Additionally, even if reintensification does not occur along the leading edge of the MCS this afternoon, most guidance suggests redevelopment does eventually occur this evening along the southern periphery of the MCV circulation as it moves into northern/central WI. Increased severe-wind probabilities (i.e. 15%) were introduced with this outlook to cover both of these potential scenarios. A small 15% hail probability was introduce to cover potential for later evening storms atop the outflow as well. Storms are possible into northern IN and the Lower MI this afternoon and evening as well, but the lower buoyancy should temper the overall coverage and magnitude in these areas. ....SD and Vicinity... A well-defined but rather weak shortwave trough is currently moving through western CO/western WY, and will continue northeastward into eastern WY/western Dakotas by this evening. Similar to yesterday, high-based storms will develop ahead of the approaching shortwave and intensify as they move eastward into a progressively more moist/unstable air mass over west-central SD. Upscale growth into another nocturnal MCS is forecast by most guidance, with the MCS tracking northeastward across western/central SD tonight. Strong to severe gusts are possible with this potential MCS across much of western/central SD. $$ = = = 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) .