Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Aug 10 2025 00:47:05 AWUS01 KWNH 100047 FFGMPD WIZ000-ILZ000-IAZ000-100645- Mesoscale Precipitation Discussion 0888 NWS Weather Prediction Center College Park MD 845 PM EDT Sat Aug 09 2025 Areas affected...Southern WI...Northern IL...Eastern IA Concerning...Heavy rainfall...Flash flooding likely Valid 100045Z - 100645Z SUMMARY...Increasing coverage of very heavy shower and thunderstorm activity is expected by later this evening and going into the overnight period. Slow-moving and locally backbuilding/training convective cells are expected. This coupled with high rainfall rates will promote areas of flash flooding, some of which may be significant. DISCUSSION...The latest surface analysis shows a well-defined outflow boundary that is nearly stationary across portions of northeast IA and across southern WI, with a rather significant cold pool situated just to the north given the earlier convective activity today. A very moist and unstable airmass though has been pooling along and just south of the boundary across eastern IA through northern IL with MLCAPE values of 2500 to 3500+ J/kg. PWs are generally on the order of 1.8 to 2.0 inches and generally suggestive of a tropical environment. The latest CIRA-ALPW data shows rather concentrated levels of moisture in the 850/500 mb layer and this further supports the overall high PW environment. This extremely favorable thermodynamic environment coupled with a gradual increase in a south to southwest low-level jet along the outflow boundary should support an uptick in convective development by later this evening. Increasing coverage of showers and thunderstorms should be most notable over southern WI where isentropic ascent/cold pool interaction will be stronger, but there is a likelihood for convection to develop and focus eventually back into areas of northwest IL and eastern IA where the nose of the low-level jet will be a bit stronger and thus indicative of stronger speed convergence. The level of moisture and instability that is in place coupled with an increase in moisture transport overnight near this outflow boundary will support extremely high rainfall rate potential that could easily reach 2 to 3 inches/hour. The environment will gradually become conducive for some backbuilding convective cells as the low-level jet strengthens, and thus concerns for cell-training will exist in time. Recent HRRR and WoFS solutions have been supporting as much as 3 to 6+ inches of rain at least locally, with the heaviest rainfall likely being over parts of southern to southeastern WI. Given the environmental setup, these rainfall totals certainly seem plausible, and locations such as Madison and Milwaukee may be impacted by these heavier totals. In time overnight, areas as far west as Dubuque, IA may see a similar threat. Given the high rainfall rate and storm total potential, areas of flash flooding are likely tonight, and some of this flash flooding may be notably significant. This will include a threat for strong urban flooding impacts. Orrison ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!9x0FEnoA_6QZM949Wm4Gt2aeSVTKLbVjsdtM1Gbw9D4fr4lH68LS4UvkPV28mRSw-Ly2= kmxAVJAoDoXZc5zj1ZImeZc$ for graphic product... ATTN...WFO...ARX...DMX...DVN...LOT...MKX... ATTN...RFC...MSR...NWC... LAT...LON 43718920 43688789 43158714 42418740 41928839=20 41349106 41629218 42519239 43219127=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) .