Flash Flood Guidance
Issued by NWS
Issued by NWS
890 AWUS01 KWNH 221735 FFGMPD TXZ000-OKZ000-222200- Mesoscale Precipitation Discussion 1042...Corrected NWS Weather Prediction Center College Park MD 134 PM EDT Sun Sep 22 2024 Corrected for Resend of Text Areas affected...Southwest to Central East OK...Southeast TX Panhandle... Concerning...Heavy rainfall...Flash flooding possible Valid 221700Z - 222200Z SUMMARY...Potential for elevated training cells with rates slowly increasing as cells approach surface front and deep moisture flux inflow. Isolated rates up to 2"/hr and totals of 2-3" may result in localized flash flooding particularly near urban or hard/baked ground conditions. DISCUSSION...16z surface analysis depicts a stationary front from TQH at the the southward sagging cold front across the MOKSAROK across to SRE to OUN to FSI and a low near FDR before becoming a bit less defined across NW Texas into deeper low level status. This stratus is banked in west of the surface low, but also within the best isentropic ascent from return Gulf moisture along the low level jet. Upper-level jet is sliding east and as such, the mid-levels quickly veering across 850-700mb resulting in convergent flow aloft of the Eastern Cap Rock into SW OK. Modest 500-1000 J/kg of MUCAPE and the FGEN forcing has been breaking out convection for the last few hours with increasing coverage across TX. Total moisture values through this eastward angling moisture plume are fairly solid at at 1.5-2 standard anomaly units above average between 1.5-1.75", but slowly climbing with the addition of the return Gulf moisture and increasing confluence into the mid-levels. As such, rainfall rates are slowly increasing from 1-1.5"/hr into an increasingly favorable steering flow allowing for training elements over the next few hours. Recent drought conditions resulting in very high FFG values are likely still too high for these rates (with exception of central Cap Rock where values are more approachable); however, as the cells move eastward, the proximity to the surface front reduces and bases are lowering and trying to root more toward the surface. This is allowing for increased moisture flux into the updrafts with Tds in the upper 60s. As a result, rainfall rates are starting to increase to around 2"/hr with some occasional as well a approaching increased urbanization. While 1hr FFG values are still above 2.5"; the prolonged drought may have further hardened the upper ground surface making infiltration even more difficult and so may be over-estimating FFG. While, not likely to be large scale or significant in magnitude, isolated flash flooding is considered possible over the early afternoon hours across the repeating/training corridor particularly near urban centers. Gallina ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...AMA...LUB...OUN...TSA... ATTN...RFC...ABRFC...WGRFC...NWC... LAT...LON 36109607 36069525 35799487 35339499 34969571 34729672 34459805 34099985 33890132 34520180 35150101 35629991 35919906 36089804 36069700