Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue May 09 2023 07:36:08 AWUS01 KWNH 090736 FFGMPD TXZ000-091200- Mesoscale Precipitation Discussion 0243 NWS Weather Prediction Center College Park MD 333 AM EDT Tue May 09 2023 Areas affected...South-Central Texas Concerning...Heavy rainfall...Flash flooding likely Valid 090730Z - 091200Z Summary...Localized rainfall rates of 1-3"/hr will likely allow for additional isolated instances of flash flooding through early morning. Discussion...Strong, slow moving thunderstorms continue to percolate across South-Central Texas, as a shortwave impulse aloft transitions to becoming a closed upper-low. While the shortwave has allowed for just enough deep layer shear (~20 kts) to keep thunderstorms modestly organized, the 850-300 mb mean flow is a measly 5-10 kts in the vicinity of the storms. This has allowed the strongest updrafts to occasionally produce rainfall rates of 2-3"/hr, though 1-2"/hr have generally been more common. A rather large cold pool has developed as a result of the merging cells over the past several hours, and storms have begun to become better organized (forming a mesoscale convective system, or MCS). It appears the MCS is beginning to finally starting to forward propagate towards the east-southeast, though the overall motion will likely remain relatively slow (at 10-15 kts) as indicated by the upwind propagation vectors. This should generally allow for localized 1-3"/hr rainfall rates to continue, which will likely allow for additional isolated instances of flash flooding through the early morning hours (affecting the metro area of San Antonio initially, and possibly affecting the Corpus Christi metro more directly towards dawn). The mesoscale environment that the MCS is moving into is characterized by plentiful instability (SB CAPE of 2000-4000 J/kg), precipitable water values of 1.3-1.7 inches (near the 90th percentile, per CRP sounding climatology), and effective bulk shear near 20 kts. While the urbanized terrain of the metro areas will be the most susceptible to flash flood impacts, the Flash Flood Guidance (FFG) across South-Central Texas indicates values as low as 2-3" (over 3-hr), largely due to rather wet antecedent conditions (as NASA SPoRT-LIS 0-40 cm soil moisture values also indicate, with much of the area over the 70th percentile and some areas over the 90th percentile). Churchill ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!9s4zeXyRuhUg_CrwlfcicklIFzRl5Z0WmulY9LsH2vy9MqbAnZsU-J6BKvAieSlsrGND= H2DR-iKusnXqt-wdcyCfgWI$ for graphic product... ATTN...WFO...BRO...CRP...EWX...HGX... ATTN...RFC...WGRFC...NWC... LAT...LON 30159842 29689706 28769563 27949670 27329716=20 27159797 27539961 29010091 29159940 30019890=20 =20=20=20=20=20=20=20=20=20=20=20=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 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .