Flash Flood Guidance
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Issued by NWS
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265 AWUS01 KWNH 290741 FFGMPD MSZ000-LAZ000-TXZ000-291340- Mesoscale Precipitation Discussion 0200 NWS Weather Prediction Center College Park MD 340 AM EDT Mon Apr 29 2024 Areas affected...Southeast TX...Central to Southwest LA...Far Southwest MS Concerning...Heavy rainfall...Flash flooding likely Valid 290740Z - 291340Z SUMMARY...Slow-moving and locally training showers and thunderstorms with extreme rainfall rates continue to impact southeast TX and areas of central to southwest LA. Flash flooding continues to be a major concern early this morning, and multiple major metropolitan areas including Houston and Lake Charles and their suburbs may see significant and life-threatening impacts as extreme rainfall advances toward the Gulf Coast. DISCUSSION...A long-lived, slow-moving, and high-impact MCS continues to gradually edge down to the southeast toward the Gulf Coast early this morning with extreme rainfall rates. The GOES-E IR satellite imagery continues to depict a very impressive cloud pattern with very cold overshooting convective tops (occasionally to -80C) with a strongly divergent and wedged signature aloft. Radar imagery shows the eastern flank of the MCS involving central LA making a bit more progress in advancing down to the southeast as a cold pool becomes better established, but unfortunately this has not been the case for many areas in southeast TX to the north and northeast of Houston where the western and southwest flanks of the convective line have exhibited only a slow and gradual push down to the southeast, with considerable cell-training and persistence of extreme rainfall rates. This has resulted in significant flash flooding overnight for a number of locations. Over the last hour, some of these extreme rainfall rates have begun to also edge into southwest LA to the north and northwest of Lake Charles as the convective line increasingly becomes aligned in a west to east fashion. The convection remains well-established along the leading edge of an outflow boundary with moderate to strong instability pooled along it which is being aided by persistently convergent and very moist low to mid-level southwest flow. MLCAPE values are still on the order of 1500 to 2500 J/kg with PWs of around 1.75 inches, and this is facilitating extremely heavy rainfall rates of as much as 2 to 3 inches/hour. Overall, the environment remains conducive for this long-lived MCS to persist through the early morning hours given the level of divergent flow aloft and persistent moisture/instability transport, and this will maintain the threat for significant rainfall totals and corresponding concerns for flash flooding. Gradually a sufficient cold pool should develop to help advance the heaviest rains offshore into the northwest Gulf of Mexico by mid-morning, but until then, areas of southeast TX and southwest LA along a line from Houston to Lake Charles and especially the northern suburbs of these metropolitan areas should see several inches of rain. The most recent HRRR guidance and the 00Z HREF consensus suggest additional totals of 3 to 6 inches with isolated heavier amounts. Consequently, more flash flooding is likely, some of which may be significant and life-threatening. Orrison ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...EWX...HGX...JAN...LCH...LIX...SHV... ATTN...RFC...LMRFC...WGRFC...NWC... LAT...LON 32119105 30979080 29819183 29589333 29439455 28909531 28649611 29059661 29889648 30499587 30999478 31389314 31949209