Flash Flood Guidance
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Issued by NWS
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894 AWUS01 KWNH 232314 FFGMPD TNZ000-KYZ000-INZ000-ILZ000-MOZ000-ARZ000-240510- Mesoscale Precipitation Discussion 1045 NWS Weather Prediction Center College Park MD 714 PM EDT Mon Sep 23 2024 Areas affected...southeastern MO/northeastern AR into Mid-MS Valley Concerning...Heavy rainfall...Flash flooding possible Valid 232312Z - 240510Z SUMMARY... The potential for SW to NE training of heavy rain will increase overnight from the eastern AR/MO border region into the and across the MS River. Rainfall rates of 1-2 in/hr are expected with totals of 2 to 4 possible on a localized basis. DISCUSSION...Fading visible satellite imagery at 23Z and regional radar imagery showed a recent increase in the intensity of thunderstorms over northern AR into MO, especially with a small line segment located between STL and UNO. Additionally, a northeastward tracking mesolow was observed in northern AR, co-located with a small area of showers to its north. The regional uptick in convection was occurring ahead of an upper level vorticity max over western MO seen on water vapor imagery, tracking ENE. At the surface, a low was located about 75 miles southwest of STL with a stationary front extending eastward into southern KY and cold front extending southward from the low into west-central AR. Earlier clearing on visible imagery ahead of the cold front from northeastern AR into southeastern MO had allowed for greater coverage of 500-1500 J/kg MLCAPE located in the warm sector over southeastern MO via SPC mesoanalysis data. Moisture via area GPS observations and mesoanalysis data revealed values of 1.5 to 1.8 inches throughout the Mid-MS Valley. As the upstream vorticity max/trough axis continue to move east overnight, thunderstorm coverage is expected to expand across southeastern MO/northeastern AR into southern IL, especially for locations near/north of the stationary front. Some modest increase in 850 mb flow is expected beyond 00Z ahead of the trough with greater coverage of 20-25 kt southwesterlies forecast through 04Z by the latest RAP which should lead to greater isentropic ascent from the MO/IL border into southern IL and western portions of KY. Due to unidirectional southwesterly flow ahead of the cold front, instances of southwest to northeast training will be favored as the general precipitation axis advances toward the east, ahead of the upstream upper vort/trough axis. Rainfall rates of 1-2 in/hr and localized maxima of 2 to 4 inches will be possible Otto ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...ILX...LSX...LZK...MEG...PAH...SGF... ATTN...RFC...LMRFC...MBRFC...NCRFC...OHRFC...NWC... LAT...LON 39338855 38468784 36748875 36378912 35798979 35479042 35419117 35679184 36149221 37119221 38239099 38998989