Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Mar 26 2025 17:15:53 AWUS01 KWNH 261715 FFGMPD TXZ000-262315- Mesoscale Precipitation Discussion 0085 NWS Weather Prediction Center College Park MD 115 PM EDT Wed Mar 26 2025 Areas affected...South-Central and Deep South TX Concerning...Heavy rainfall...Flash flooding possible Valid 261715Z - 262315Z SUMMARY...Developing and expanding clusters of heavy showers and thunderstorms are expected through this afternoon. Very heavy rainfall rates and locally slow cell-motions will support an increasing flash flood threat. DISCUSSION...The midday GOES-E satellite imagery shows a well-defined mid-level shortwave trough ejecting east across northwest mainland Mexico which will begin to cross the Rio Grande Valley by later today. Increasingly divergent flow aloft ahead of these height falls along with some smaller scale vort energy will be gradually overspreading the lower Rio Grande Valley and adjacent areas of south-central TX and will be interacting with an increasingly moist and unstable airmass. MLCAPE values over much of the region are already locally on the order of 1500 to 2000 J/kg, with PWs of 1.5 to 1.75 inches. Persistent low-level south-southeast flow will continue to bring moisture up across much of southern TX in general going through the afternoon hours, and the latest CIRA-ALPW and MIMIC-TPW data sets show notable concentrations of deeper and more anomalous moisture advecting into the lower Rio Grande Valley ahead of the upstream mid-level height falls/shortwave energy. This will set the stage for developing and expanding clusters of heavy showers and thunderstorms going through the afternoon hours. The convective cells in this moistening environment should become increasingly efficient and will be capable of producing very high rainfall rates considering the level of instability and some uptick in updraft helicity parameters. The 12Z HREF guidance suggests the stronger and more organized convective cells may be capable of producing 2 to 3 inch/hour rainfall rates. A combination of multicell and some isolated supercell structures are generally expected to evolve over time, and some of the cells that become more deeply rooted are expected to potentially become very slow-moving with cell-motions a bit to the right of the deeper layer mean flow. This will support some locally enhanced rainfall totals, with some rainfall totals by early this evening of 3 to 5+ inches possible. Antecedent conditions are very dry, but with such high rainfall rates and potential for slow cell-motions, the threat for flash flooding will be increasing with time. Additional MPDs will likely be required this evening to further address the excessive rainfall threat going into the overnight hours. Orrison ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!4aPFlnQ_WWQm9hc6kTt-06RSX7IdGQfndG2Vwt8UA4aR2YV7FEW9O1vcMKua9pksn0_Q= EPjdyCFI2HiIQV1Rz1KgAYQ$ for graphic product... ATTN...WFO...BRO...CRP...EWX... ATTN...RFC...WGRFC...NWC... LAT...LON 29289749 28919687 28229668 27529713 27149726=20 26709731 26009720 25929757 26109820 26369895=20 26729931 27479964 27839989 28240022 28800007=20 29279882=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) .