Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Aug 11 2025 04:24:41 AWUS01 KWNH 110424 FFGMPD WIZ000-ILZ000-IAZ000-110900- Mesoscale Precipitation Discussion 0901 NWS Weather Prediction Center College Park MD 1223 AM EDT Mon Aug 11 2025 Areas affected...northern Illinois through central Wisconsin Concerning...Heavy rainfall...Flash flooding possible Valid 110423Z - 110900Z Summary...Showers and thunderstorms expanding ahead of a shortwave will likely train across parts of Wisconsin tonight. Rainfall rates of 1-2"/hr at times will produce 1-3" of rainfall, and may result in renewed flash flooding. Discussion...The GOES-E IR imagery tonight shows expanding convection evident via cooling cloud tops across parts of northern Illinois and southern Wisconsin. These thunderstorms are generally developing in response to the overlap of a shortwave analyzed by the RAP and noted in the satellite imagery lifting across eastern IA, with the slow veer of an 850mb LLJ analyzed by regional VWPs to be 20-30 kts from the S/SW. This LLJ is drawing elevated PWs northward, which were measured via the 00Z U/A soundings at DVN and ILX to be above 1.9 inches, or well above the 90th percentile for the date. These PWs are aligned with a ribbon of high MUCAPE above 2000 J/kg, and as the LLJ continues around 30 kts the next several hours, these robust thermodynamics will resupply an environment favorable for heavy-rain producing convection. Recent radar-estimated rainfall rates from KMKX have been as high a 1.5"/hr, and the HREF neighborhood probabilities for 1"/hr remain as high as 40% through around 09Z, while the HRRR indicates an isolated potential for brief 3"/hr rain rates (0.75"/15min). The strongest convection is likely during the next few hours, primarily across southern WI, before the LLJ begins to veer. This is also when the greatest height falls/PVA will occur downstream of the shortwave as it lifts northeast, providing enhanced ascent into the favorable thermodynamics. There may be two areas of focused heavier rainfall, one across central WI and a secondary maximum in southeast WI. Across central WI, the LLJ nose will develop leading to enhanced convergence before it begins to veer after 07Z. This suggests regenerating cells in this region with enough support from thermodynamic advection to produce repeating 1"/hr rain rates. With cells likely strengthening right along this convergent axis, rainfall could reach 1-3" leading to isolated instances of flash flooding within a narrow corridor. Farther south in WI and into far northern IL, the greatest isentropic ascent is likely, which will act into a plume of the most intense MUCAPE. Here, propagation vectors collapse to around 5 kts and become aligned obliquely right of the mean wind suggesting backbuilding cells and a higher training threat. Rain rate probabilities also peak in this vicinity, and the HREF 6-hr rainfall probabilities for 3" rise above 15%. Southern WI has also experienced tremendous rain the past 24-hrs of 2-5", and in some areas more than 9" of rain, leading to extremely vulnerable soils such that any heavy rain could quickly lead to runoff and instances of flash flooding. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!_3v1zRJNRvp-j3FKUYPjRVhvGbxMCsh4UlA9MC-EWaAO33e92oTzGb6w6MjJBQ3xGOED= QYViyd1hxpt_9-5SRx_1Czs$ for graphic product... ATTN...WFO...ARX...DVN...GRB...LOT...MKX... ATTN...RFC...MSR...NWC... LAT...LON 45258843 45058781 44668756 44198757 43318773=20 42818781 42348803 41878897 41819016 42209087=20 42559100 43419084 44409024 45008936=20 =3D =3D =3D 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) .