Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Feb 12 2025 20:31:47 AWUS01 KWNH 122031 FFGMPD ALZ000-MSZ000-LAZ000-130215- Mesoscale Precipitation Discussion 0031...Corrected NWS Weather Prediction Center College Park MD 331 PM EST Wed Feb 12 2025 Corrected for updated graphic Areas affected...Lower Mississippi Valley through Northern Alabama Concerning...Heavy rainfall...Flash flooding possible Valid 122024Z - 130215Z Summary...Showers and thunderstorms rapidly blossoming within a warm sector will expand in coverage and intensify through the afternoon. These thunderstorms will lift northward and then train SW to NE ahead of a cold front, with rainfall rates as much as 2-3"/hr. This could lead to instances of flash flooding. Discussion...The regional radar mosaic across the Gulf Coast this afternoon depicts rapidly expanding and intensifying thunderstorms along and just south of a warm front from LA to the FL Panhandle. This convection is expanding within a pronounced warm sector characterized by favorable instability (MLCAPE 1000-2000 J/kg) and elevated PWs (1.6 to 1.8 inches) according to the SPC mesoanalysis. Additionally, recent VWPs from the region indicate modest low-level veering but with strong inflow, supporting large updrafts capable of producing intense rainfall rates. This is being analyzed by recent MRMS 15-min rainfall as high as 0.75" (3"/hr rates), resulting in rising CREST unit streamflow values across parts of LA and MS. Upstream of this fresh convection, a wave of low pressure and attendant cold front are analyzed by WPC crossing from TX into LA, along which additional thunderstorms are occurring with current FFWs. As the afternoon progresses into the evening, the environment should become increasingly unstable as the plume of 1000-2000 J/kg MLCAPE surges as far north as Birmingham, concurrent with elevated PWs being drawn northward. This plume of robust thermodynamics will be advected on 850mb inflow that is progged to reach 50+ kts, resulting in 850-700mb moisture flux that may exceed 5 sigma according to the SREF. Additionally, increasing synoptic lift within the RRQ of an intensifying jet streak will support an expansion of convection into the evening, with thunderstorms likely aligning along or just ahead of the convergence axis of the approaching cold front as it squeezes the warm sector. This alignment will rapidly enhance the flash flood risk, as training of cells along the boundary will offset the limiting storm speed of 40-60kts. The HREF suggests that coverage of rainfall rates exceeding 1"/hr will expand, and the HRRR 15-min progs suggest rainfall intensity may produce 0.75 to 1 inch of rain in as little as 15 minutes. These rates themselves could cause instances of flash flooding, but where training occurs, more than 3" of rain is possible, enhancing the flash flood risk. The most likely locations for any flash flooding will be across urban areas as soil moisture in southern LA, MS, AL is drier than normal according to NASA SPoRT. However, training of these intense rain rates could quickly overwhelm even the drier soils, so flash flood instances are possible anywhere across the discussion area into this evening. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!5MQOgaXrGVUoKPJkQubelxBuZyrEYS24uHQXIN3l7yhjsj_2rwva_5FCBl-uLT7SYJgF= n5-HZtHsTQA859vPlm0_hRI$ for graphic product... ATTN...WFO...BMX...HUN...JAN...LCH...LIX...MEG...MOB...SHV... ATTN...RFC...LMRFC...SERFC...NWC... LAT...LON 34828712 34538627 33658599 32878613 32308688=20 31708793 31268939 30989077 30979206 30969237=20 31009261 31569255 32349167 34568837=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) .