Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Jul 08 2023 06:59:49 AWUS01 KWNH 080659 FFGMPD TNZ000-KYZ000-ILZ000-MOZ000-ARZ000-081200- Mesoscale Precipitation Discussion 0661 NWS Weather Prediction Center College Park MD 259 AM EDT Sat Jul 08 2023 Areas affected...Southeast Missouri, Northeast Arkansas Concerning...Heavy rainfall...Flash flooding possible Valid 080658Z - 081200Z Summary...Clusters of extremely slow moving thunderstorms will continue overnight across parts of Missouri, possibly diving into Arkansas. Rainfall rates will likely eclipse 2"/hr at times, resulting in locally 2-4" of rain. Flash flooding is possible. Discussion...The local radar out of KSGF indicates a few scattered but extremely slow moving thunderstorms just west of the Missouri Bootheel. These thunderstorms are being driven by ascent downstream of a shortwave rotating through a mean longwave trough, producing height falls and thickness diffluence over the region. This ascent is occurring into a favorable thermodynamic environment characterized by PWs approaching 2 inches and MUCAPE of more than 2000 J/kg. 850mb inflow within the LLJ is locally backed to the SSW at 20 kts downstream of the approaching shortwave, helping to resupply moisture into the developing convection, and produce radar-estimated rain rates of 2-2.5"/hr. This has resulted in scattered FLASH responses of 130% QPE:FFG ratio and CREST unit streamflows above 200 cfs/mi. The high-res guidance is struggling to handle the ongoing convection which has produced several FFWs across Missouri already. Recent runs of the HRRR are completely missing the ongoing activity, so the forecast relies more heavily on the ARWs and ingredients. As the shortwave continues to trek eastward, the LLJ should continue to pulse to 20-30 kts but begin to veer as the best height falls shift farther east. This should result in convective cells dropping farther south, but could maintain intensity as thermodynamics remain robust. Additionally, this veering of the low-level inflow will help to collapse Corfidi vectors to 5 kts or less, with some anti-parallel motion noted in the RAP. This will likely continue to manifest as a few clusters of thunderstorms organized through 20-25 kts of effective bulk shear backbuilding into greater instability to result in very little motion. With HREF rain rates progged to exceed 2"/hr, this will likely yield isolated rainfall amounts of 2-4" before convection wanes towards morning. Although the convection is not progged to become widespread, it may feature a bit more coverage than guidance indicates. This could continue to pose an isolated flash flood threat as storms will move very slowly atop soils that in some places are saturated from 7-day rainfall of 150-200% of normal according to AHPS. HREF FFG exceedance probabilities are modest, mostly due to limited coverage and a lack of model consensus, but it is likely where these storms stall, soils will become overwhelmed to result in rapid runoff and isolated instances of flash flooding. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!7ty33NhQTYr3DlhyZWUrRjn-SJPewKYH4D8VhRLCn1azbTbWp0aLL9Hg_lU9ElQfA6cu= 6xV1Oz4mgAXQcT8-jTo5WM0$ for graphic product... ATTN...WFO...LSX...LZK...MEG...PAH...SGF... ATTN...RFC...LMRFC...MBRFC...NCRFC...NWC... LAT...LON 38149122 37879022 37268946 36718927 36318929=20 35788952 35328995 35119076 35339131 35749184=20 36299208 36989205 37829163=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) .