Subj : MESO: Heavy Rain/Flooding To : All From : Mike Powell Date : Wed Jan 24 2024 09:26:00 AWUS01 KWNH 241221 FFGMPD MSZ000-LAZ000-241819- Mesoscale Precipitation Discussion 0026 NWS Weather Prediction Center College Park MD 720 AM EST Wed Jan 24 2024 Areas affected...portions of LA and southern MS Concerning...Heavy rainfall...Flash flooding likely Valid 241219Z - 241819Z Summary...A pair of convective lines are producing heavy rainfall. Hourly rain totals to 3" with local amounts to 6" are possible. Discussion...Active lines of showers and thunderstorms are moving ahead of a cold front quicker than the guidance expected across portions of LA and MS, with some evidence of line echo wave pattern noted, implying the presence of mesocyclones. Inflow at 850 hPa is 50 kts per VAD wind profiles out of the south- southwest. Precipitable water values are near or above 1.75". The storms are utilizing ML CAPE where CIN is near zero across southern LA and MU CAPE where CIN exists farther north. MU CAPE of 500-1500 J/kg is present per SPC mesoanalyses, and advancing northward. Heavy rain rates are occuring a bit farther north than indicated by the 06z HREF guidance across MS, which is concerning. The guidance indicates that progression will be held up at times both by the near unidirectional flow out of the southwest with height and by embedded mesocyclones, with a larger scale wave across southern LA potentially holding up progression for a time across MS. The tail end of the activity will tend to slow, waiting for the incoming cold front/upper level trough to approach from the west. The ingredients support the potential for hourly rain totals to 3" and local amounts to 6", with amounts in the northern portions of the discussion area expected to outperform guidance, as seen recently. High rain rates are expected to be caused by cell mergers, training, and embedded mesoscyclones holding up the convective line from time to time. While the heavy rain is moving into an area that has been dry this past week, this degree of heavy rainfall should overwhelm the three hourly flash flood guidance. The bigger issues are expected in urban areas. Roth ATTN...WFO...JAN...LCH...LIX...MOB... ATTN...RFC...LMRFC...SERFC...NWC... LAT...LON 33038999 32808877 31428865 29978985 29459169 29679300 31089220 32379105 = = = --- SBBSecho 3.14-Linux * Origin: Ilink: CCO - capitolcityonline.net (454:1/105) .