Subj : MESO: Heavy rain - floodi To : All From : Mike Powell Date : Thu Apr 20 2023 18:55:00 AWUS01 KWNH 202322 FFGMPD TXZ000-210500- Mesoscale Precipitation Discussion 0201 NWS Weather Prediction Center College Park MD 721 PM EDT Thu Apr 20 2023 Areas affected...South-Central TX to near TX/LA Border Concerning...Heavy rainfall...Flash flooding possible Valid 202320Z - 210500Z Summary...Localized hourly rainfall rates of 1-3" may allow for additional isolated instances of flash flooding through evening. Discussion...Deep convective activity is ongoing across much of south-central Texas, encompassing much of the TX Triangle and portions of the TX Hill Country (including the cities of San Antonio, Austin, and College Station). A localized flash flood threat in association with this convection is expected to continue through evening, with current rainfall rates in association with the strongest updrafts averaging 1-2"/hr rates (though a particularly strong storm south of Waco is producing rates as high as 2-3"/hr). Vigorous overshooting tops were noted via GOES-East visible/infrared sandwich imagery, with above-anvil cirrus plumes also noted with the strongest updrafts. These are good signs of convective longevity, and with precipitable water values of 1.4-1.7 inches (near the max moving average per FWD sounding climatology), SB CAPE of 2000-4000 J/kg, and effective bulk shear of 35-45 kts, convection should have no trouble staying strong and relatively organized. Semi-discrete, multicell clusters are expected to dominate before convection becomes better linearly organized along the cold front this evening (while also likely gradually becoming more progressive). Recent HRRR runs (hourly from 16-21z) have been fairly persistent in depicting additional localized totals of 2-4" through 05z. These runs have been a bit more aggressive than the HREF probability-matched mean (PMM) QPF through the same time period, but that seems to make sense given that the HRRR is better assimilating the ongoing storms (which have tended to be much stronger than the 18z HREF had indicated through 23z). Given these observational trends and the consistency of recent HRRR runs, expect these 2-4" localized totals to be realized, with some local maxima possibly reaching 4-6". These totals would be most problematic over more sensitive metropolitan areas (such as the aforementioned San Antonio/Austin and College Station), but the Hill Country will be somewhat more sensitive as well with flash flood guidance (FFG) near 3" over 3-hr (and as low as 4-5" across non-metropolitan areas in central TX). Churchill ATTN...WFO...EWX...FWD...HGX...LCH...SHV...SJT... ATTN...RFC...WGRFC...NWC... LAT...LON 32079681 32069557 31829437 30999386 29949563 29789684 29229772 28839873 29269985 30379935 31089840 = = = --- SBBSecho 3.14-Linux * Origin: Ilink: CCO - capitolcityonline.net (454:1/105) .