Flash Flood Guidance
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Issued by NWS
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343 AWUS01 KWNH 262036 FFGMPD KYZ000-INZ000-ILZ000-MOZ000-ARZ000-270235- Mesoscale Precipitation Discussion 0329 NWS Weather Prediction Center College Park MD 435 PM EDT Sun May 26 2024 Areas affected...Portions of the Middle MS and Lower OH Valleys Concerning...Heavy rainfall...Flash flooding likely Valid 262035Z - 270235Z SUMMARY...Numerous areas of showers and thunderstorms will be redeveloping and expanding in coverage over the next several hours across areas of central and southern MO and into southern IL, western KY, and southwest IN. Given locally wet/saturated soil conditions from earlier rainfall, and the additional rainfall threat this evening, areas of flash flooding are expected with some of it locally significant. DISCUSSION...The mid-afternoon GOES-E Day Cloud Phase RGB satellite imagery shows convective initiation taking place across areas of west-central to southwest MO in close proximity to a surface cold front gradually settling southeast into the middle MS Valley. The airmass ahead of this across much of central and southern MO continues the process of recovering in the wake of the strong early-day QLCS activity which left behind a strong cold pool. The modification of this cold pool over the last few hours continues with strong solar insolation/heating and warm air advection focusing ahead of a wave of low pressure advancing into southwest MO. This has allowed for the erosion of earlier low-level CIN, and has fostered MLCAPE values back as high as 2000 to 3000 J/kg. Convection is expected to rapidly develop and expand in coverage across areas of central and southern MO over the next 2 to 3 hours and advance generally off to the east into adjacent areas of southern IL, southwest IN, and western KY heading through the mid-evening hours as this downstream airmass also recovers from the remnants of the aforementioned cold pool. A well-defined outflow boundary/front remains in place across portions of southern MO and down into western TN which should gradually return northeastward over the next several hours and also be a catalyst for convective redevelopment as a moist/unstable 30 to 40 kt southwest low-level jet interacts with it. Rainfall rates with the redeveloping showers and thunderstorms are expected to reach 1.5 to 2.5"/hour given the return of higher CAPE values, moisture convergence in vicinity of the aforementioned fronts/boundaries and favorable shear. A notable concern for cell-training exists in close proximity to the aforementioned outflow boundary in particular, which will likely set the stage for areas of southeast MO, southern IL, southwest IN, and western KY to see the heaviest focus of rainfall going into the evening hours. The 12Z HREF, 12Z NSSL-MPAS guidance, and the 18Z/19Z experimental WoFS runs suggest additional rainfall totals going through mid-evening may reach 3 to 6 inches, although there are notable differences with the placement of the heaviest totals. Given the wet antecedent conditions from heavy rainfall over the last 12 to 18 hours, these additional rains are likely to cause significant runoff concerns with scattered to numerous instances of flash flooding, and locally considerable impacts going into the evening hours. Orrison ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...ILX...IND...LMK...LSX...MEG...PAH...SGF... ATTN...RFC...ABRFC...LMRFC...MBRFC...NCRFC...OHRFC...NWC... LAT...LON 39398837 39248695 38628616 37728628 37148709 36788811 36489013 36579283 36979375 37599391 38229322 38709200 39209016