Flash Flood Guidance
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Issued by NWS
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587 AWUS01 KWNH 121747 FFGMPD MSZ000-LAZ000-TXZ000-122345- Mesoscale Precipitation Discussion 0258 NWS Weather Prediction Center College Park MD 146 PM EDT Sun May 12 2024 Areas affected...East Texas into Central Louisiana Concerning...Heavy rainfall...Flash flooding possible Valid 121745Z - 122345Z SUMMARY...Flash flooding threat continues over east Texas while expanding into central Louisiana into this evening as scattered heavy thunderstorms shift east along a low level boundary. DISCUSSION...Radar imagery at 1730Z depicts an expanding cluster of elevated heavy thunderstorms over east Texas north from the northern Houston metro where a warm front is approaching. This activity continues moving east as persistent 35kt SWly deep layer mean flow is counteracted by Wly upwind propagation vectors. Rainfall of 1" has been estimated over the past hour with the easternmost cell that is approaching the LA border. Cells farther west are producing around 1"/hr rates, but overlap with a swath of 2-3" extending east from Waco. Elevated instability remains somewhat limited (but sufficient) at 1000-1500 J/kg of MUCAPE. Upper level SWly flow is from a positively-tilted trough still over CO/NM that is advecting Pacific moisture in across Mexico while low level flow over the warm front is bringing moist flow from the western Gulf of Mexico with PWs in east Texas of 1.8-2.1" which is 3 sigma above normal. HRRR runs starting at 15Z have been more disperse with rainfall over this area than the 13/14Z runs, but the rapid development of heavy thunderstorms in waves coming off the warm front and over rather sensitive areas north of Houston from extreme rainfall over the past couple weeks. 3hr FFG is generally 2.5 to 3.5" in the sensitive area north of Houston and closer to 4" into central LA. The main limitation remains shear with Wly 0-6km bulk shear values now 60kt which should maintain a somewhat scattered convective mode. However, given the sensitivity of the area north of Houston, localized flash flooding should be expected there. Rainfall of 3-4" is possible in central LA where flash flooding is also possible. This warm front stalls this evening, so further heavy rain and flash flooding threats are forecast across this area overnight. Jackson ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...FWD...HGX...JAN...LCH...LIX...SHV... ATTN...RFC...LMRFC...WGRFC...NWC... LAT...LON 31869571 31829405 31589237 31269152 30499167 30259267 29889415 30069579 31589672