Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Nov 21 2023 04:39:49 AWUS01 KWNH 210439 FFGMPD FLZ000-ALZ000-MSZ000-LAZ000-211020- Mesoscale Precipitation Discussion 1181 NWS Weather Prediction Center College Park MD 1139 PM EST Mon Nov 20 2023 Areas affected...central Gulf Coast into central MS/AL Concerning...Heavy rainfall...Flash flooding possible Valid 210436Z - 211020Z SUMMARY...Training of heavy rain will continue a flash flood threat across portions of the central Gulf Coast into central MS/AL through 11Z. Rainfall rates of 1 to 2+ in/hr are expected and localized totals of 3 to 5 inches will be possible. DISCUSSION...04Z radar imagery across the Lower Mississippi Valley showed a broken line of thunderstorms extending from the central MS/AL border to coastal LA near Vermilion Bay, within the warm sector of a frontal system connected by two areas of low pressure. The primary low over north-central MS appears to be maintaining intensity while a secondary low over western LA has been dropping south and weakening over the past 3 hours. The resulting southward push of the cold front along the MS/LA border has helped orient the line of convection more SW to NE versus WSW to ENE. Given the mean steering flow has more of a westerly component compared to the current orientation of the broken line of thunderstorms, training potential has reduced compared to earlier Monday evening. However, a localized flash flood threat will continue across southeastern LA into southern MS and portions of southwestern/central AL over the next few hours. An estimated 500-1500 J/kg MLCAPE remained within the warm sector (00Z area soundings and SPC mesoanalysis data from 04Z) along with PWATs of 1.5 to 1.7 inches which should continue to support rainfall rates of 1 to 2 in/hr, locally higher. Short term RAP forecasts show 30 to 50 kt of 850 mb flow maintaining robust moisture transport toward the north along with the continuation of at least 500 to 1000 J/kg MLCAPE within the warm sector. While the cold front should begin to sweep toward the east at a steady pace overnight, where northern portions of pre-frontal convection are able to race ahead relative to convection to the immediate south, favorable line orientation to the deeper layer mean wind will allow training and the possibility of localized flash flooding. Rainfall rates of 1-2 in/hr will be common within the line of storms, but rates locally over 2 will also be possible where idealized training is able to set up. Dry antecedent conditions across this area of the U.S. and associated high FFGs should limit flash flooding to areas of exceptional training and/or overlap of high rates atop urban areas. Otto ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!7kB4BMHNwZNqbfPN3bEg-wg8ymvEav2bLlkyjKseg7Gzg3GhcKuklth1tIRugcg79LFE= RhLnZlm7dB0H-kYLxLDFrvk$ for graphic product... ATTN...WFO...BMX...JAN...LCH...LIX...MOB... ATTN...RFC...LMRFC...SERFC...NWC... LAT...LON 33748696 33088683 32158687 31158702 30698708=20 30218732 29308848 29018925 29079064 29369132=20 29669181 30269178 31279085 31958998 32478924=20 33408818 33718749=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) .