Flash Flood Guidance
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Issued by NWS
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160 AWUS01 KWNH 180735 FFGMPD MNZ000-SDZ000-NDZ000-181330- Mesoscale Precipitation Discussion 0458 NWS Weather Prediction Center College Park MD 334 AM EDT Tue Jun 18 2024 Areas affected...central SD into eastern ND and northern MN Concerning...Heavy rainfall...Flash flooding possible Valid 180730Z - 181330Z Summary...Areas of heavy rain will continue to advance through the Dakotas into MN through sunrise. Peak rainfall rates of 1 to 2 in/hr, locally higher, are expected to produce additional but localized 2-4 inch totals through about 13Z, which may result in isolated to widely scattered coverage of flash flooding. Discussion...Regional radar imagery at 07Z showed a nearly continuous line of thunderstorms extending from eastern ND into west-central SD. The line has generally progressing toward the east at a steady enough pace to limit flash flood concerns but short term areas of training have supported rainfall rates of 1-2 in/hr, locally higher, since 04Z according to MRMS. The higher rates have primarily been focused over SD where eastward progression of the convective line has been slower. The axis of convection was largely elevated, positioned north of a warm front over eastern SD within a zone of strong elevated convergence located between 850 and 700 mb. Precipitable water values were anomalous across the northern Plains, with 00Z area soundings showing values near the 90th percentile but since 00Z, low level moisture advection via a 60-70 kt 850 mb jet has further increased moisture along with CAPE values. 07Z SPC mesoanalysis data showed MUCAPE values ranged from 1500 J/kg over northern MN to an impressive 4000 J/kg over northeastern SD. As a mid-level trough over MT and western WY continues to advance east this morning, the NE to SW oriented axis of thunderstorms will advance through the Dakotas into MN, maintaining the threat for 1 to 2+ in/hr rainfall rates. Synoptic scale lift in the form of enhanced divergence and diffluence aloft will be maximized over eastern ND into northern MN within the right entrance region of an upper level jet max over southern Manitoba which will support increased ascent but eastward progression of thunderstorms may limit heavy rainfall duration. RAP guidance supports weakening of the elevated convergence axis as an 850 mb low organizes over the Dakotas through 12Z, with the surface and 850 mb warm front lifting north toward the Canadian border. Through 13Z, there will be the potential for SW to NE training where mean steering flow aligns with the orientation of convection, perhaps better focused across southern areas where eastward progression will be slower compared to northern locations. These instances of training are expected to remain short lived, but could still support short term rainfall of 2-4 inches along with isolated to widely scattered areas of flash flooding. Otto ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...ABR...BIS...DLH...FGF...FSD...MPX...UNR... ATTN...RFC...MBRFC...NCRFC...NWC... LAT...LON 49439524 49419467 48999350 48729223 48019116 46899227 45119559 44219801 43780049 43710170 43810236 44040249 44460233 45570060 46509950 47609805 48339708 48799640 49229589