Flash Flood Guidance
Issued by NWS
Issued by NWS
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643 AWUS01 KWNH 290246 FFGMPD LAZ000-TXZ000-290845- Mesoscale Precipitation Discussion 0198 NWS Weather Prediction Center College Park MD 1045 PM EDT Sun Apr 28 2024 Areas affected...Southeast TX through Northwest LA Concerning...Heavy rainfall...Flash flooding likely Valid 290245Z - 290845Z SUMMARY...Backbuilding and training showers and thunderstorms across southeast TX and northwest LA are expected to continue to produce areas of extreme rainfall over the next several hours. Flash flooding will continue locally, and parts of southeast TX in particular are expected to see significant and locally life-threatening impacts. DISCUSSION...GOES-E IR satellite imagery shows a very strong cold-topped convective wedge signature over southeast TX with persistent areas of backbuilding and training showers and thunderstorms. Overshooting top activity with cloud top temperatures occasionally as cold as -70C have been noted in a southwest to northeast fashion from Brazos County to Trinity County. Additional areas of strong, and slow-moving convection are situated also farther northeast into northwest LA. The convection is situated along a well-defined outflow boundary with moderate to strong instability pooled along it which is being aided by convergent and moist low to mid-level southwest flow. MLCAPE values are on the order of 1500 to 2500 J/kg with PWs of around 1.75 inches, and this is helping to yield extremely heavy rainfall rates of as much as 2 to 4 inches/hour. Enhanced upper-level divergence over the region is noted in the IR/WV satellite imagery loops, and the southwest flank of the ongoing axis of convection is expected to be an area over the next few hours where convection is likely to continue to regenerate and train over the same area. Already there have been rainfall totals locally of 4 to 8 inches in areas of southeast TX, and with the expectation of additional extreme rainfall over the next several hours, some areas especially in between northeast Brazos, northern Grimes, northern Walker and Trinity Counties may see rainfall totals reach 8 to 12+ inches. Recent runs of the HRRR guidance have been insisting on this extreme rainfall potential, and as a result, significant and locally life-threatening flash flooding is expected going through a portion of the overnight period. WPC has upgraded a portion of the MPD area to a Moderate Risk of excessive rainfall the D1 ERO given the ongoing satellite and radar trends. Orrison ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...EWX...FWD...HGX...LCH...SHV... ATTN...RFC...LMRFC...WGRFC...NWC... LAT...LON 32899280 32619241 31929238 31109324 30529433 30069594 30319671 30689666 31449616 32139531 32729404 32869352