Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Aug 17 2025 08:30:33 AWUS01 KWNH 170830 FFGMPD INZ000-ILZ000-171300- Mesoscale Precipitation Discussion 0950 NWS Weather Prediction Center College Park MD 429 AM EDT Sun Aug 17 2025 Areas affected...Northeast Illinois...Northwest Indiana... Concerning...Heavy rainfall...Flash flooding possible Valid 170830Z - 171300Z SUMMARY...Isentropic ascent within remaining unstable/moist environment continues. Additional 1.5-3" totals training in proximity of Chicago and suburbs will keep risk of incidents of flash flooding possible through daybreak. DISCUSSION...GOES-E 10.3um IR loop shows much of northern IL has remained untapped through the overnight period. This is confirmed by recent RAP analysis fields with 2500-3000 J/kg of MUCAPE across N IL. Surface analysis continue to show affects of initial evening complex of return southeasterly flow with remnants of a boundary angled NW to SE from far NW IL toward DNV, which given recent elevated convective lines through Chicagoland; seems to be reinforced with steepened isentropes from north to south. This while VWP at DVN and LOT/ORD shows generally west and west-northwest 15-25kts orthogonal to the boundary. RADAR shows a few upstream cells redeveloping given the stronger moisture flux in the upglide through N IL. Moisture remains more than ample given Tds in the low to mid 70s from the source while mid-level moisture/RH remains solid for a core of 2"+ total PWats through the ascent plane. As such, thunderstorms will have solid vertical moisture loading to continue to support 2"/hr rates. Deep layer steering starts to curl anti-cylonically along the northeast edge of the deeper ridging, and convection has been bending right of mean flow becoming parallel to the IND/IL border. Though further southward, the inflow/upglide weakens and becomes displaced from the core of unstable air, so cells have been generally weakening further south or eastward, and this is likely to continue throughout the early morning, limiting the risk for additional heavy rainfall toward northeast IL/Northwest IND.=20 Currently LLJ strength is strong and with heavy rainfall/cold pool generation closer to the Lakeshore, westward propagation and closer to surface rooting of cells may limit path of newer development to train over earlier tracks, but there will remain some intersection for an additional 1-3" with newer cells; combine that with proximity to urban environment near Chicago and increased run-off make it more probable that incidents of flash flooding/rapid inundation remain possible through the early morning hours. Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!5xAMj4-01uIHivdK-1pSE1hmvhDQfj2cxMRA2KrmTQ_coF3ArZdVaoWhH8TCLPPffO3V= ItuQiImU_QGYmK5y4pYxYFM$ for graphic product... ATTN...WFO...ILX...IND...IWX...LOT... ATTN...RFC...MSR...TIR...NWC... LAT...LON 42418859 42148785 41108660 40248662 40088755=20 40518816 41288894 42248930=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) .