Flash Flood Guidance
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Issued by NWS
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497 AWUS01 KWNH 200113 FFGMPD TXZ000-200601- Mesoscale Precipitation Discussion 0470 NWS Weather Prediction Center College Park MD 912 PM EDT Wed Jun 19 2024 Areas affected...South Texas Concerning...Heavy rainfall...Flash flooding possible Valid 200111Z - 200601Z Summary...Convective rainbands along the outer periphery of Tropical Storm Alberto continue to stream into South Texas. Rainfall amounts of 2-5" could lead to some instances of flash flooding through 6z. Discussion...Radar continues to track several bands of tropical convection entering South Texas as Tropical Storm Alberto continues a westward track into northeast Mexico. Recent banded convection close to the Texas coastline exhibited cooling cloud tops accompanied by an uptick in radar estimated rain rates to 1.5-2"/hr per MRMS and KCRP. This confined area of enhanced convection likely remains tied to an inverted trough along the coastline, with plenty of low-level convergence and 2000 J/kg of MLCAPE within a tall and skinny profile (NCAPE around .1). Moreover, effective SRH upwards of 200 m2/s2 will support shallow supercell structures to dynamically enhance rainfall rates (see SPC MD 1336 for more on the severe weather threat), with 2.6-2.7" PWATS noted in the inflow region of these cells. Over the next several hours, the inverted trough is expected to migrate inland, advecting 1000-1500 J/kg MLCAPE across South Texas. This will allow for the more efficient bands containing 2-2.5"/hour rainfall rates to move across South Texas. Where the most organized bands persist, rainfall of 2-5" could fall through 6z. Generally, the overall impacts with this activity will likely depend on if any bands can train over areas which saw heavy rainfall earlier today along the coastline, where 5-9" of rainfall is estimated over the last 12 hours. Further inland across South Texas, some flash flood issues also remain possible through 6z, as the HREF suggests an appreciable (30-40%) chance of 10 year ARI exceedence, with some signal (10-15%) for 100 year ARI exceedences also noted. Asherman ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...BRO...CRP...EWX... ATTN...RFC...WGRFC...NWC... LAT...LON 28839698 28659664 28229656 27369721 26679722 26019712 25799736 25909811 26269896 26659928 27119958 27639992 28099981 28369892 28679782