Flash Flood Guidance
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Issued by NWS
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987 AWUS01 KWNH 160731 FFGMPD WIZ000-ILZ000-MNZ000-IAZ000-161320- Mesoscale Precipitation Discussion 0446 NWS Weather Prediction Center College Park MD 330 AM EDT Sun Jun 16 2024 Areas affected...IA into southeastern MN/western WI, far northwestern IL Concerning...Heavy rainfall...Flash flooding possible Valid 160729Z - 161320Z Summary...Localized flash flooding will remain possible for portions of the Upper Mississippi Valley through 13Z. Training of heavy rain may allow for rainfall rates as high as 3 in/hr but 1-2 in/hr rates should be most common. Additional rainfall of 2-4 inches is expected over the next 6 hours, but with much of that falling within a 3 hour period or less. Discussion...A combination of satellite and radar imagery showed two primary MCVs over the Upper Mississippi Valley with active areas of showers and thunderstorms nearby as of 07Z. The first was over IA, roughly 70 miles northeast of DSM, with slower moving and a few repeating cells to the west of the MCV. The second MCV was over western WI, about 70 miles east-northeast of MSP while a third, smaller MCV, was identified about 10 miles northwest of MSP. Recent thunderstorm development was noted over southern MN...between the MCV centers...within a strong warm advection pattern, where 40 to 50+ kt south-southwesterly 850 mb winds were overrunning a pair of warm fronts as depicted on the 06Z WPC surface analysis. SPC mesoanalysis data showed precipitable water values of 1.6 to 1.8 inches across the region (near the climatological max PW for mid-June at MPX) and MUCAPE of ~500 to 1000 J/kg. However, instability weakened with northeastern extent into WI, limiting rainfall intensity east of the Mississippi River. A general northeastward motion is expected with the MCVs over the next 3-6 hours and continued warm advection with 850 mb jet speeds peaking near 50 kt from the western half of IA into southeastern MN is forecast by the RAP through 12Z. Some increase in instability is anticipated toward the northeast with continued low level moisture transport, and given the anomalous moisture present and modest upper level diffluence over the region, maintenance of localized heavy rain is expected through the morning. Where cells align within the steering flow, training will allow for rainfall rates of 1-2 in/hr, but localized rates near 3 in/hr cannot be ruled out. An additional but localized 2-4 inches of rain is expected across portions of the Upper Mississippi Valley through 13Z which may result in flash flooding. Otto ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...ARX...DLH...DMX...DVN...GRB...LOT...MKX...MPX... ATTN...RFC...MBRFC...NCRFC...NWC... LAT...LON 46069261 46049062 45019007 43758965 42838926 41988927 41498998 41359139 41479340 41999492 43289487 44509445