Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Sep 17 2023 15:08:36 AWUS01 KWNH 171508 FFGMPD INZ000-ILZ000-171905- Mesoscale Precipitation Discussion 1080 NWS Weather Prediction Center College Park MD 1106 AM EDT Sun Sep 17 2023 Areas affected...Northeast IL...Far Northwest IN Concerning...Heavy rainfall...Flash flooding possible Valid 171505Z - 171905Z SUMMARY...Heavy rainfall from locally intense bands of showers and a few thunderstorms may continue to foster some concerns for flash flooding for a few more hours. DISCUSSION...Radar and surface observations show a compact area of low pressure over the southern end of Lake Michigan this morning which in conjunction with a rather strong mid-level vort center is helping to produce rather slow-moving bands of heavy showers and a few thunderstorms. Heavy rains have already been impacting the Chicago metropolitan area over the last few hours, and some additional heavy rains are expected at least in the short-term as a new band of heavier rainfall currently north of the city begins to drop south down along the lakeshore. Radar and satellite imagery also are showing areas of new convection developing near Gary, IN. All of this activity is generally aligned with notably convergent low-level flow with an axis of frontogenetic forcing in place around the western flank of the surface low and a fair amount of mid-level deformation helping to provide deeper layer ascent. The rainfall rates with this morning's activity have been heaviest out over Lake Michigan, but some occasional rates reaching 1 to 1.5 inches/hour have been impacting areas along and just inland from the lake. A driver of some of these heavier rates has been a modest pooling of surface-based CAPE reaching 500+ J/kg around the lakeshore and over southern Lake Michigan itself. This instability is being aided by relatively warm SSTs that are on the order of 70F to 72F. The convection should tend to linger at least for a few more hours, and will be capable of producing locally an additional 2 to 3 inches where these bands of stronger convection set up and locally train over the same area. The activity should begin to weaken by early to mid-afternoon as the surface low and upper support begin to pull away. Nevertheless, areas in between Chicago, IL (ORD) and Gary, IN adjacent to the lake and inclusive of the urban corridors may see additional flash flooding concerns in the short-term. Orrison ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!8tECEltGIjLOSGUms3mYFKs0BVddL2L7QTMLJaf9IWRt18iQ-3I5uPXa5dv7GFgwzeq-= BmFeUELod6hmrfdAG7jOt_o$ for graphic product... ATTN...WFO...IWX...LOT... ATTN...RFC...NCRFC...NWC... LAT...LON 42478797 42378779 42058768 41758748 41618693=20 41338702 41318758 41538798 41968822 42328820=20 =20=20=20=20=20=20=20=20=20=20=20=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 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .