Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Jul 18 2023 17:14:57 AWUS01 KWNH 181714 FFGMPD KYZ000-ILZ000-MOZ000-182300- Mesoscale Precipitation Discussion 0757 NWS Weather Prediction Center College Park MD 114 PM EDT Tue Jul 18 2023 Areas affected...Missouri, southern Illinois, far western Kentucky Concerning...Heavy rainfall...Flash flooding possible Valid 181713Z - 182300Z Summary...Showers and thunderstorms will intensify along a low-level convergent axis through the afternoon before an MCS sweeps through to the southeast. This convection will likely train with 1-2"+/hr rain rates, producing locally more than 3 inches of rain. Flash flooding is possible. Discussion...The regional radar mosaic this aftn shows a pair of MCSs with accompanying MCVs moving southeast across Missouri. The lead MCS has left a low-level convergent boundary in its wake, into which subtly backing flow downstream of the second MCV is impinging more orthogonally to drive ascent. This is resulting in an expanding line of convection with radar-estimated rain rates of 1.5-2"/hr according to KLSX. The environment across the area is characterized by PWs of 1.7-1.9 inches within the pre-convective environment, and MUCAPE of 2000 J/kg just south of this line. This locally backed low-level flow will continue to transport these thermodynamics northward into the boundary and along the impressive SBCAPE gradient, and convection is likely to persist until the second MCV sweeps through later this aftn. The high-res guidance is unfortunately very different in its evolution of the simulated reflectivity fields today. As the 850mb flow backs more to the south and increases to 15-20 kts, it should drive the best CAPE northward while also isentropically ascending the remnant convergent boundary. With impressive PWs remaining in place, these ingredients suggest convection will redevelop across this axis and then train to the southeast on boundary parallel 0-6km mean winds of 20-30 kts. Additionally, effective bulk shear increasing to 50-60 kts will allow for increasing storm organization, driving rain rates to 2"/hr or more at times. While the heaviest rain is likely along this axis before the MCS sweeps through later today, locations that receive training along the boundary and the subsequent MCS, could receive more than 3 inches of rain before precip winds down this evening. Confidence in the exact placement of the heaviest axis is modest, but HREF EAS probabilities for more than 1 inch peak above 25% along and just northeast of the surface boundary. Recent rainfall across this part of Missouri and southern Illinois has been more than 300% of normal according to the 7-day AHPS rainfall departures. This has lowered FFG to 1.5"/1hr and 2.5"/3hrs which may be exceeded in the most pronounced training. This could result in instances of flash flooding before the MCS sweeps through and brings an end to precipitation from NW to SE by this evening. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!_QNw1YziYOQtY8WtYavKCdGrEEF16Ms6YtgyU7YqzEvBCeQhqxklPmd9jhzMhMG3e9xu= 10jAdrplB2eMciefRIkZPvw$ for graphic product... ATTN...WFO...EAX...LSX...MEG...PAH...SGF... ATTN...RFC...LMRFC...MBRFC...NCRFC...OHRFC...NWC... LAT...LON 38859389 38579133 38289020 37948900 37668851=20 37288842 36818868 36588907 36539013 37059173=20 37639309 38099392 38359441 38679433=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) .