Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Jun 12 2025 08:00:43 AWUS01 KWNH 120758 FFGMPD TXZ000-121300- Mesoscale Precipitation Discussion 0423 NWS Weather Prediction Center College Park MD 358 AM EDT Thu Jun 12 2025 Areas affected...TX Triangle region into the Middle and Upper TX Coast Concerning...Heavy rainfall...Flash flooding likely Valid 120755Z - 121300Z Summary...Localized hourly rainfall totals as high as 3-4" expected to continue into mid-morning. Numerous instances of flash flooding are likely (some life threatening to locally extreme) with additional localized totals of 6"+ expected (with 8"+ amounts possible). Discussion...Clusters of thunderstorms are in the process of growing upscale into a mesoscale convective system (MCS) across western portions of the TX Triangle region, from the San Antonio area northeastward to near Waco. Storms are generally organizing linearly along the southern and eastern periphery of the established cold pool, where instability is greatest (1000-3000 J/kg of SBCAPE) with increasing low-level moisture transport (in association with a strengthening nocturnal low-level jet with 925mb winds of 25-30 kts from the SSE). PWs have also increased to a very impressive 1.9-2.3 inches, nearing daily max record levels (using CRP sounding climatology as a proxy). Localized hourly rainfall totals are estimated to be as high as 3-4" (per MRMS), a resulting of training (as deep layer steering flow is oriented nearly parallel to the cold pool boundary, due to the favorable placement of a mid-upper level low) and warm rain processes dominating (with wet bulb zero heights around ~13k feet). Storms training from west-to-east (along the southern edge of the cold pool) in the vicinity of San Antonio are particularly concerning, given the flooding sensitivities of the metro area. Meanwhile, a separate cluster of thunderstorms are growing in strength and coverage near the Middle TX Coast (where PWs are maximized) due to the strengthening low-level jet and associated warm-air advection/isentropic ascent. Storms should only continue to organize this morning, given the very favorable aforementioned environment (with differential divergence only increasing further over the next several hours). Hi-res models (both the 00z HREF and experimental 18z REFS ensembles) are in excellent agreement with both the expected magnitudes and placement of QPF with relatively high probabilities (40-60%) for both localized 5" exceedance (40-km neighborhood) and 1" exceedance overlap (10-100 km Ensemble Agreement Scale). This corresponds with high FFG exceedance probabilities (up to 60-70%) and a decent chance (up to 25-35%) of locally exceeding 100-yr ARIs. Given this strong ensemble signal, localized 6"+ totals are expected (and it is notable that hourly HRRR/RRFS runs have been fairly consistent in depicting localized 8"+ totals, primarily between the Corpus Christi and Houston metros where repeating heavy rainfall is most likely). Numerous instances of flash flooding are likely, some of which are expected to be life threatening. Given the potential for 100-yr ARI exceedance, extreme instances of localized flash flooding are possible (with areas that do not typically flood at risk of experiencing flash flooding). Churchill ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!6DZOWV8JTor6182-ZxpoyfYaoFai91QBvupthK3DBZ1DNtJWghSvIB1PH6QwNHseSWq2= nCBg5hmAlLFXqBUNJ3MydBY$ for graphic product... ATTN...WFO...CRP...EWX...FWD...HGX...SHV... ATTN...RFC...FWR...NWC... LAT...LON 32049643 31979551 31329461 29789487 29099531=20 28689613 28389719 28619862 29179932 29799937=20 30279846 30989817 31929747=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) .