Flash Flood Guidance
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Issued by NWS
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181 AWUS01 KWNH 201918 FFGMPD MNZ000-IAZ000-NEZ000-SDZ000-210115- Mesoscale Precipitation Discussion 0473 NWS Weather Prediction Center College Park MD 316 PM EDT Thu Jun 20 2024 Areas affected...Central and Eastern SD...Far Northwest IA...Southwest MN Concerning...Heavy rainfall...Flash flooding possible Valid 201915Z - 210115Z SUMMARY...A general increase in the concentration of showers and thunderstorms can be expected this afternoon and evening. Heavy rainfall coupled with increasingly moist antecedent conditions may result in some areas of flash flooding by this evening. DISCUSSION...A gradual strengthening of warm air advection through the afternoon and evening hours coupled with the stronger transport of moisture and instability in an elevated fashion along and north of a warm front should encourage additional areas of showers and thunderstorms to develop. GOES-E IR satellite imagery already shows broken areas of cold-topped convection across areas of southern and eastern SD, with some pockets of repeating cell-activity. MUCAPE values of locally 500 to 1000 J/kg are currently in place near the active areas of convection, with positive 3-hourly MUCAPE differentials continuing to increase with time. A southerly low-level jet of 20 to 30 kts is nosing up across northern NE toward southern SD, but this should increase in strength this afternoon and especially early this evening to as much as 30 to 40+ kts. PWs are forecast to increase to locally over 2 standard deviations above normal with values reaching well over 1.5 inches by early this evening across central and eastern SD along with adjacent areas of northwest IA and southwest MN. Subtle shortwave energy ejecting out of the High Plains will be crossing the region over the next several hours and this will interact with the increasingly favorable thermodynamic environment associated with the strengthening warm air advection regime to yield more expansive areas of convection that will also be conducive for heavier rainfall rates. The 12Z HREF supports rainfall rates reaching as high as 1.5 inches/hour, with some additional storm totals through 00Z (7pm CDT) of 2 to 4 inches. Given the increasingly moist antecedent conditions, there may be some areas of flash flooding by this evening. A much more organized threat of heavy rain from strong convection is expected late this evening and the overnight period, and thus additional MPDs will be issued accordingly. Orrison ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...ABR...DMX...FSD...LBF...MPX...OAX...UNR... ATTN...RFC...MBRFC...NCRFC...NWC... LAT...LON 45349764 45209561 44529426 43619417 43029550 42839731 42969873 43360030 44070095 44580067 45069949