Flash Flood Guidance
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Issued by NWS
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898 AWUS01 KWNH 181845 FFGMPD WIZ000-MNZ000-SDZ000-NDZ000-190043- Mesoscale Precipitation Discussion 0460 NWS Weather Prediction Center College Park MD 243 PM EDT Tue Jun 18 2024 Areas affected...Portions of the Upper Midwest Concerning...Heavy rainfall...Flash flooding possible Valid 181843Z - 190043Z SUMMARY...Redeveloping bands of heavy showers and thunderstorms are expected through the afternoon and early evening hours. Some training of this activity may result in runoff problems and concerns for flash flooding. DISCUSSION...Surface observations show a wave of low pressure over northeast SD which will be lifting across west-central to northeast MN this afternoon as an upper-level trough gradually ejects east across the northern High Plains. A strong low-level jet reaching 40 to 50+ kts out ahead of this low pressure system will be interacting with a warm front across central to northeast MN to drive a renewed threat of rather organized showers and thunderstorms going through the afternoon and early evening hours. In the wake of earlier convection, the latest visible satellite imagery shows some clearing taking place over areas of central and southern MN, and already the MLCAPE values have recovered to 2000 to 3000 J/kg. An additional uptick in instability is expected over the next few hours with more diurnal heating, and with increasing convergence along the warm front along with enhanced isentropic ascent and frontogenetical forcing, there should be an uptick and expansion of convection for areas along and north of the warm front. Areas of central to northeast MN in particular will likely see concerns for rather well-organized and locally training bands of convection given this set-up and with convection aligned parallel to the deeper layer steering flow. However, as warm-sector boundary layer destabilization continues in conjunction with relatively strong shear parameters, there will eventually be the development of surface-based convection along and just ahead of the approaching upstream cold front. The 12Z HREF guidance supports rainfall rates that are quite high, and capable of reaching 2.0 to 2.5 inches/hour. The latest CIRA-ALPW data shows a pronounced area of enhanced moisture concentrated in the 850/700mb layer with strong LVT magnitudes. Therefore the stronger convective cells are expected to be quite efficient in producing high rainfall rates. Additional rainfall totals by 00Z (7pm CDT) this evening will be capable of reaching 3 to 6 inches with much of this connected to the training convection threat north of the warm front. However, warm-sector areas of southern MN may also see locally as much as 2 to 4 inches of rain as convection here organizes later in the afternoon ahead of the cold front. Given the locally wet antecedent conditions and additional totals, some runoff problems and concerns for flash flooding will exist. Orrison ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...ABR...DLH...FGF...FSD...MPX... ATTN...RFC...MBRFC...NCRFC...NWC... LAT...LON 48529091 47918980 46969050 46219132 45169218 43659372 43619558 44129618 44949646 45619679 46529665 47429552 48019423 48469287