Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Jul 21 2024 02:52:51 AWUS01 KWNH 210252 FFGMPD ALZ000-MSZ000-LAZ000-TXZ000-210800- Mesoscale Precipitation Discussion 0676 NWS Weather Prediction Center College Park MD 1052 PM EDT Sat Jul 20 2024 Areas affected...Southwest Louisiana through Central Alabama Concerning...Heavy rainfall...Flash flooding possible Valid 210251Z - 210800Z Summary...Thunderstorms will persist and increase in coverage along a stationary front into the overnight. Rainfall rates of 2-3"/hr are likely, which through slow motion could produce 2-3" of rain with locally higher amounts. Flash flooding is possible. Discussion...The regional radar mosaic this evening shows a slow expansion of higher reflectivity aligned SW to NE from far southwest Louisiana through central Alabama. This convection is blossoming within favorable deep layer ascent driven by convergence along a stationary front analyzed by WPC, modest isentropic ascent on a weak LLJ emerging from the Gulf of Mexico, and upper diffluence within the RRQ of an upper jet streak. Together, this impressive lift is occurring into favorable thermodynamics characterized by PWs above 2.15", or the 90th climatological percentile, and MLCAPE of 1000-2000 J/kg. Radar-estimated rain rates have been 1.5-2"/hr according to KHDC WSR-88D beneath rapidly cooling cloud tops noted via the GOES-E IR imagery. During the next several hours, the 850mb LLJ should at least subtly intensify from its current 10 kts to 15-20 kts as progged by the RAP, which will advect even more impressive moisture northward while driving additional isentropic ascent. Although subtle backing of the wind may occur in the vicinity of any weak impulses within the flow aloft, in general the LLJ should veer into the front to drive impressive moisture confluence, resulting in a narrow corridor of thunderstorms with intense rainfall rates. Both the HREF and REFS ensembles indicate a 30-40% chance of 1"/hr rates, and although the 2"/hr probabilities are just 5-10%, this is likely underdone as the individual CAMs comprising the ensembles are generally too low with current coverage and intensity. The ingredients based approach suggests that the current activity will persist and may even intensify as thermodynamics remain impressive in the region of strengthening ascent. Bulk shear is weak, so strong organization of cells is not likely, but repeating rounds of heavy rainfall is expected as the mean 0-6km winds are aligned to the front and to the weak Corfidi vectors, suggesting training from SW to NE across the area. Where multiple rounds of storms occur, rainfall could reach 2-3" with locally higher amounts. FFG remains elevated across this area except in AL where it is locally compromised to 1.5-2"/3hrs. Although HREF FFG exceedance probabilities are modest, the intensity of these rates suggest rapid runoff is likely, especially in any urban areas or over locally more saturated soils, which could result in instances of flash flooding. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!8ARwgUCHBGogRmYBgXWOX9ZTJ_cWtLkfDLWN2NdfioMrx1HOr9HHGRElmsYSRjgLXjUk= 1bx3fxFRSyck_HdYkrbBAME$ for graphic product... ATTN...WFO...BMX...JAN...LCH...LIX...MOB...SHV... ATTN...RFC...LMRFC...SERFC...WGRFC...NWC... LAT...LON 32898684 32818594 32178615 31748694 31258853=20 31088912 30679011 30389090 30039225 29929324=20 29949381 30189385 30539365 31569194 32249030=20 32408976 32808818=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .