Flash Flood Guidance
Issued by NWS
Issued by NWS
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086 AWUS01 KWNH 211506 FFGMPD WIZ000-MNZ000-IAZ000-NEZ000-SDZ000-212105- Mesoscale Precipitation Discussion 0479 NWS Weather Prediction Center College Park MD 1105 AM EDT Fri Jun 21 2024 Areas affected...Northern NE...South-Central to Southeast SD...Northwest IA...Southern MN Concerning...Heavy rainfall...Flash flooding likely Valid 211505Z - 212105Z SUMMARY...Redeveloping bands of heavy showers and thunderstorms are expected going through the early to mid-afternoon hours. These rains are expected to largely fall over areas that have seen very heavy rainfall recently, and are therefore extremely sensitive to additional rains. Given the wet/saturated conditions on the ground, instances of renewed flash flooding are likely heading into the afternoon hours. DISCUSSION...A wavy quasi-stationary front remains draped across the region from central NE through northern IA with multiple waves of low pressure riding east along it. In the wake of overnight convection, there has been a relative lull in activity over the last couple of hours, but the latest GOES-E IR satellite imagery and dual-pol radar data does show a couple of new linear bands of elevated convection beginning to focus across northern NE and also southeast SD, far northwest IA, and southwest MN. Some additional expansion of elevated convection north of the front is expected going through mid-afternoon as shortwave energy gradually ejects east out across the High Plains and helps facilitate some larger scale ascent/divergent flow aloft along with a persistent southerly to southwest low-level jet of 20 to 30 kts overrunning the front and yielding isentropic ascent and frontogenetical forcing. MUCAPE values in vicinity of the regenerating rounds of convection are on the order of 500 to 1000 J/kg, with a very moist environment (PWs around 1.75 inches) in place that is supportive of efficiently heavy rainfall rates. Going through the mid-afternoon hours, some of the stronger elevated storms may drive rainfall rates upwards of 1.5 to 2 inches/hour. Some cell-training is expected given the orientation of the convection with the deeper layer west-southwest mean layer flow. The new 12Z HREF guidance is suggesting the potential for as much as an additional 2 to 4 inches of rain with isolated heavier amounts going through mid-afternoon. Given the wet/saturated soil conditions, elevated streamflows, and lingering impacts from heavy rainfall last night, these additional rains over the next several hours are highly likely to renew areas of flash flooding. This will especially be the case along portions of the I-90 corridor from southeast SD through southern MN including the Sioux Falls vicinity. Orrison ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...ABR...ARX...DMX...FSD...LBF...MPX...OAX...UNR... ATTN...RFC...MBRFC...NCRFC...NWC... LAT...LON 44799457 44699254 44239183 43699208 43249344 42919612 42399845 42170010 42340135 42930149 43490063 44019907 44469696