Flash Flood Guidance
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Issued by NWS
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948 AWUS01 KWNH 250346 FFGMPD TNZ000-KYZ000-MSZ000-MOZ000-ARZ000-TXZ000-OKZ000-250945- Mesoscale Precipitation Discussion 0320 NWS Weather Prediction Center College Park MD 1145 PM EDT Fri May 24 2024 Areas affected...much of AR and surroundings into the Mid-South Concerning...Heavy rainfall...Flash flooding likely Valid 250345Z - 250945Z Summary...Mesoscale convective system (MCS) will continue to produce hourly accumulations of 1-2" overnight likely resulting in localized totals of 2-5", scattered instances of flash flooding. Discussion...An MCS has taken shape over central and southern AR late this evening, consisting of a complex mix of storm modes with embedded supercells, surging bow echos, and backbuilding multicell clusters. The most intense component as of late is a northeastward rapidly propagating bow echo, possibly the result of an earlier storm split (favoring the left-mover vector, as upwind and downwind propagation vectors favor a southwesterly propagation). Out ahead of this newly propagating bow echo, earlier storms that formed and followed a southeasterly motion have produced localized totals of 2-4" over portions of the MS Delta/Alluvial Plain. FFGs have been diminished as a result of this earlier precipitation, generally ranging from 1.5-2.5"(for 3-hr period) over more sensitive soils (and a bit higher at 2.0-3.0" over the less saturated soils of northeast AR and southwest TN). With expected peak hourly accumulations of 1-2", new (or renewed) instances of flash flooding should be easily achieved. The mesoscale environment clearly will continue to support storms through a good portion of the overnight period with instability little diminished (ML CAPE ranging from 2000-3000 J/kg), PWATs at near record levels for late May (per SPC sounding climatology with a range of 1.5-1.9"), effective bulk shear of 35-45 kts, and moderate moisture transport via a locally strong (25-30 kt) LLJ. Fresh 00z HREF guidance is handling the convective activity reasonably well, though the HRRR in particular is struggling to properly initialize the core of the strongest convection. That said, the 40-km neighborhood probability fields for 2" and 3" thresholds is rather impressive (through 09z), indicating 20-60% and 15-35% maximized probabilities over much of the Mid-South. Given the observational trends, highly favorable parameter space, and relatively sensitive soils, scattered instances of flash flooding are considered likely (with localized totals of 3-5" expected over the Mid-South, i.e. the red hatched area, and 1-3" localized totals generally expected elsewhere within the MPD). Convection is expected to be fading across the area by 10z as instability is gradually exhausted. Churchill ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...JAN...LSX...LZK...MEG...PAH...SGF...SHV...TSA... ATTN...RFC...ABRFC...LMRFC...NWC... LAT...LON 37099085 36228874 34288902 33359078 33139161 33069259 33139380 33369431 34079476 35689450 36479316