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Flash Flood Guidance
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Issued by NWS
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325 AWUS01 KWNH 160047 FFGMPD TNZ000-KYZ000-INZ000-ILZ000-MOZ000-ARZ000-160646- Mesoscale Precipitation Discussion 0883 NWS Weather Prediction Center College Park MD 847 PM EDT Thu Aug 15 2024 Areas affected...Southern MO..OH River Valley Concerning...Heavy rainfall...Flash flooding possible Valid 160046Z - 160646Z Summary...Convective clusters are developing across portions of southern Missouri and the Ohio River Valley. Periodic cell training with rainfall rates of 2-2.5"/hr could lead to a few instances of flash flooding tonight as additional storms form. Discussion...Satellite and radar mosiac across the northern fringes of the Ozarks and Ohio River Valley highlight expanding thunderstorm coverage on the periphery of a shortwave to the north in the Missouri Valley. Recently, a thunderstorm cluster was exhibiting signs of reduced forward motion and cell training over southern Illinois, leading to elevated CREST Streamflows of 100-200 cfs/smi. Throughout the afternoon, a lack of robust forcing has kept the area dry. The recent uptick in thunderstorm coverage can likely be attributed to the approach of the shortwave working in tandem with several weak convergence zones. Owing to strong surface heating and moisture advection today, mesoanalysis estimates show 3000 J/kg MLCAPE, negligible CIN, and 2-2.1" PWATs in the vicinity of these cells to foster new development with rainfall rates upwards of 2-2.5"/hr. As new updrafts form along a west-east axis over the next several hours, 20-25 kts of westerly effective shear parallel to the convection is expected to support periods of training clusters. There is some disagreement within the 18z CAM suite as to where the main axis of training sets up tonight, which will likely depend on cold pool evolution as additional storms form. Even with lingering uncertainty regarding the placement of the heaviest rainfall, there is a general consensus for 2-4" rainfall totals through 6z tonight in the highlighted area, leading to a 25-30% chance of 6 HR QPF exceeding the 10 year ARI. While southern Illinois and western Kentucky have been quite dry, portions of south-central Missouri are comparatively more saturated (relative soil moisture around 60-65%) and may be more susceptible to runoff issues. Asherman ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...LSX...LZK...MEG...OHX...PAH...SGF... ATTN...RFC...LMRFC...MBRFC...NCRFC...OHRFC...NWC... LAT...LON 38458970 38158776 36838748 36328885 36399153 36909338 37889353 38339243