Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Aug 12 2025 09:58:42 AWUS01 KWNH 120958 FFGMPD FLZ000-ALZ000-MSZ000-LAZ000-121430- Mesoscale Precipitation Discussion 0917 NWS Weather Prediction Center College Park MD 558 AM EDT Tue Aug 12 2025 Areas affected...Central Gulf Coast through central Alabama Concerning...Heavy rainfall...Flash flooding possible Valid 120957Z - 121430Z Summary...Showers and thunderstorms streaming onshore will train north this morning. Rainfall rates of 2-3"/hr are likely, which could produce 2-4" of rain along the immediate coast. This may cause flash flooding. Discussion...The regional radar mosaic early this morning shows an expansion of showers with isolated thunderstorms across the northern Gulf. Although instability continues to be modest onshore (MUCAPE 500-1000 J/kg inland from the coast) a sharp instability gradient exists across the FL Panhandle westward to the coasts of AL and MS. Recent analysis of 850mb winds from the regional VWPs and the SPC RAP analysis indicate the inflow has increased to 20-30 kts with some local backing to the SE, leading to increasing N-S oriented convergence which is helping to drive lines of convection pushing onshore. At the same time, weak MCVs noted in reflectivity and a surface trough analyzed by WPC are helping to enhance ascent locally as well. Ascent into the area will remain impressive through morning, and may actually intensify as the 850mb LLJ reaches 1.5x the mean wind (850mb winds to 30 kts, mean wind to 20 kts) forcing more broad lift. This ascent will act upon thermodynamics that will become increasingly robust through extreme PWs measured by GPS above 2.3 inches and MUCAPE which will gradually expand inland both through the 850mb transport but also in response to daytime heating. Together, this suggests that convection will continue push onshore, while gradually spreading northward in response to the strengthening instability. The high-res CAMs have struggled this morning to resolve the ongoing activity, which is more widespread and intense than any available guidance. However, the recent HRRR runs have started to catch on and insist that convection will become widespread later this morning. This appears likely, and as the environment becomes more thermodynamically rich, rainfall rates will likely reach 2-3"/hr as progged by both HREF neighborhood probabilities and the HRRR 15-min rainfall accumulation. More concerning to the flash flood risk will be that storms will likely train repeatedly south to north as mean 0-6km winds of 10-15 kts suggest progressive cells, but propagation vectors aligned anti-parallel and into the Gulf indicate backbuilding potential. Where this training is most prolonged, 2-4" of rainfall is possible through the morning. FFG across this area is quite high at 3-4"/3hrs, and HREF FFG exceedance probabilities are generally below 15%. However, where any of these narrow training bands persist, especially if they occur over urban areas, instances of flash flooding may result, with the greatest potential occurring along the immediate coast. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!9mGE-pFkZny07w97O8ihRpXeXudfjyAWcejdl_7aYyLFwRq-vDMdHTt969QEt-t5BnRH= GQLDve1h_KI3zL_cashyD_0$ for graphic product... ATTN...WFO...BMX...HUN...JAN...LIX...MEG...MOB...TAE... ATTN...RFC...ALR...ORN...NWC... LAT...LON 34128738 33708648 33128592 31628530 30388504=20 30028536 30118611 30178665 30218707 30088793=20 29498858 29138887 28928913 28978948 29128970=20 29118999 29259022 29589018 29918978 30208937=20 30458887 30738836 31338817 32178815 33098835=20 33918831=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 3.28-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .