Flash Flood Guidance
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Issued by NWS
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670 AWUS01 KWNH 170559 FFGMPD MNZ000-IAZ000-NEZ000-SDZ000-171030- Mesoscale Precipitation Discussion 0450 NWS Weather Prediction Center College Park MD 159 AM EDT Mon Jun 17 2024 Areas affected...northeastern NE into southeastern SD, northwestern IA and southwestern MN Concerning...Heavy rainfall...Flash flooding likely Valid 170558Z - 171030Z Summary...Training of thunderstorms is likely to produce areas of flash flooding from near/north of the eastern SD/NE border into southwestern MN and northwestern IA through 10Z. 1 to 2+ in/hr rainfall rates are expected along with additional totals of at least 2 to 4 inches. Discussion...A WSW to ENE axis of thunderstorms was observed on regional radar imagery at 0530Z from the central NE/SD border into southeastern SD. MRMS-derived peak hourly rainfall has been in the 2.0 to 2.5 inch range over southern Tripp and Gregory counties in southern SD over the past 2 hours with 3-hr estimates of 4 to 5+ inches as steering flow oriented parallel to the thunderstorm axis has allowed for training. The thunderstorm axis was elevated to the north of a slow moving front that extended SW to NE from southwestern NE into southern MN at 05Z, located at the nose of stronger 850-700 mb winds averaging 30-50 kt from the south. SPC mesoanalysis data from 05Z showed the elevated convergence axis and thunderstorms along a CAPE gradient containing 1000-2500 J/kg MUCAPE. Aloft, lift was being enhanced by placement within the right-entrance region of a 100 kt jet near 200 mb (sampled by GOES East DMVs). The strong elevated convergence axis is expected to translate ENE along the elevated frontal boundary, reaching southwestern MN by 10Z out ahead of an advancing 700-500 mb shortwave currently over the central High Plains. The axis of low level forcing should lift north gradually as the surface front edges north later this morning but some southward propagation of convection will be possible into the inflow. The RAP is forecasting the upper level jet max to strengthen through 12Z, reaching 120 kt by 12Z from eastern ND into northern MN, allowing a region of strong divergence and diffluence to set up over the Missouri and Big Sioux River Valleys. While mean steering flow is not forecast to perfectly align with the axis of convergence throughout the next 4 hours, there will likely continue to be areas of training from WSW to ENE with rainfall rates of at least 1-2 in/hr. Additional rainfall totals of at least 2 to 4 inches are expected for portions of the eastern SD/NE border into southwestern MN/northwestern IA as the flash flood threats expands through the overnight. Otto ...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 44579428 44159356 43359377 42599492 42229721 42669864 42680014 42920086 43470055 44289693