Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed May 10 2023 06:26:32 AWUS01 KWNH 100626 FFGMPD TXZ000-101220- Mesoscale Precipitation Discussion 0249 NWS Weather Prediction Center College Park MD 224 AM EDT Wed May 10 2023 Areas affected...Portions of South-Central Texas into the Middle/Upper Texas Coast Concerning...Heavy rainfall...Flash flooding likely Valid 100620Z - 101220Z Summary...Localized training/repeating of rainfall rates as high as 2"/hr will likely lead to isolated to scattered instances of flash flooding though dawn. Discussion...A nearly stationary upper-level low continues to slowly meander northeastward over the Texas Hill Country early this morning. A line of showers and thunderstorms has been reinvigorated to the southeast of this upper-low center over the past couple of hours, as deep layer moisture flux convergence becomes more concentrated due to modestly strengthening low-level confluent flow. The mesoscale environment along and ahead of this strengthening area of convection is characterized by 500-1500 J/kg of SB CAPE, precipitable water values of 1.4-1.7 inches (between the 75th and 90th percentile, per CRP sounding climatology), and effective bulk shear of 20-35 kts. This environment should continue to foster convective organization through dawn, with the 850-300 mb flow allowing for relatively slow forward motions (15-20 kts) towards the east-northeast. Stronger discrete cells have already taken on some deviate motion towards the east-southeast (near the expected bunkers right motion) at an even slower forward moition of 10-15 kts. Given the nearly stationary nature of the upper-level low/forcing, there may be some backbuilding of convection as activity continues to proliferate, and localized repeating of rainfall rates of up to 2"/hr is the main concern for flash flooding. CAMs have been rather persistent in depicting a developing threat of excessive rainfall towards dawn, as the 00z HREF has come-in alarming close to the prior 12z solution. The probability-matched mean (PMM) QPF indicates a localized threat of 3-6" through dawn (12z), as also indicated by a 20-30% bullseye for 3" exceedance over the next 6 hours (located between Austin and Victoria). A closer inspection of the individual HREF members indicates a fair amount of spatial spread, despite this consistent signal. In addition, subsequent runs of the HRRR have similarly varied rather dramatically with the placement of 2-3"+ amounts. Given short-term observational trends (and more recent runs of the HRRR), the 00z HREF PMM QPF maxima may be just a tad too far northwest. Therefore the highest confidence area for realizing localized totals in excess of 3" is judged to be between Houston and Victoria through 12z, likely shifting eastward towards the Houston metro beyond 12z. Given the relatively wet antecedent conditions (as indicated by NASA SPoRT-LIS 0-40 cm soil moisture as high as the 90th percentile), isolated to scattered instances of flash flooding are considered likely. Churchill ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!-HMXAdrKX66sYmkOAI0wF-O01qE5d0VRvh9WPlKvVKMVhmCwyS2921Elr3oDsbJo3uwz= v_DVX-j2lNO3KbKrqUKwyik$ for graphic product... ATTN...WFO...CRP...EWX...FWD...HGX... ATTN...RFC...WGRFC...NWC... LAT...LON 30669663 30219545 29029536 28119677 28029781=20 28139832 28589835 28949805 29269781 29689758=20 30049752 30449728=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) .