Flash Flood Guidance
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Issued by NWS
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224 AWUS01 KWNH 282252 FFGMPD TXZ000-290400- Mesoscale Precipitation Discussion 0338 NWS Weather Prediction Center College Park MD 651 PM EDT Tue May 28 2024 Areas affected...Lower Pecos Valley...Southern Edwards Plateau into South-central Texas... Concerning...Heavy rainfall...Flash flooding possible Valid 282250Z - 290400Z SUMMARY...Strong thunderstorm cluster continues to grow with increasing moisture flux from tongue of enhanced moisture coming through the Rio Grande Valley. Localized totals of 2-4" pose possible flash flooding DISCUSSION...GOES-E Visible and EIR depict a broad and strong cluster with a few overshooting tops breaking through the expanding canopy across the Lower Pecos River Valley. Large hail/severe signatures have dominated this cluster, but recent trends note a slow transition toward higher rainfall production (with continued more numerous hail stones, to help clog culverts/drainage areas). Recent surface analysis shows dry line continues to retrograde under influence of enhanced eastward flow behind the outflow boundary from this morning`s North to Southeast TX MCS. While this has been more of a stabilizing influence a bit to the north in the core of the cooler surface air; gaps in the canopy continue to show some low level cu from Kerr/Bandera county north of the boundary, suggesting some of the higher theta-E air from the western Gulf remains and supports moderately unstable air being advected toward the complex. Sfc to boundary layer inflow of 15-25kts with enhanced moisture nearing 1.75" PW through the entire depth (though focused mainly in the lowest levels). Also, winds appear to be generally confluent to enhanced convergence to support maintenance of the complex as it propagates southeastward. So with ample unstable air and moisture being fluxed in and cluster likely moistening the local environment; rainfall efficiency will increase and likely reach sub-hourly rates of 1-2". WoFS members and HRRR 15-minute rates suggest 1-1.5" in short duration. Current orientation of the updrafts also suggest potential for short-term repeating, especially as the upstream flanking line will try to keep redeveloping with the retrograding dry line. As such, tracks of 2-4" of rainfall in 1-2 hours are possible. This brings the complex over lower FFG values of the Lower Pecos River into Southern Edwards Plateau. Confidence remains moderate to moderately-low; as Hi-Res CAMs have continued to struggle. However, recent runs of the WoFS do suggest means of 2-3" for the mean; while 90th percentiles are reaching at or slightly above 4" especially near the Pecos River as the cells remain slower moving/propagating in proximity to the dry line retrograding. So this adds some confidence to suggest flash flooding remaining possible across the area of concern through 04z. Also, of note, will be closely monitoring the complex over the Serranias del Burro and trends as it emerges into South Texas. Gallina ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...EWX...MAF...SJT... ATTN...RFC...WGRFC...NWC... LAT...LON 31040126 30820010 30309866 29599828 29079874 29089995 29750118 30030191 30090214 30490255 30960207