Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Jun 27 2023 20:41:38 AWUS01 KWNH 272041 FFGMPD SDZ000-NDZ000-MTZ000-WYZ000-280240- Mesoscale Precipitation Discussion 0597 NWS Weather Prediction Center College Park MD 440 PM EDT Tue Jun 27 2023 Areas affected...Northern Great Plains Concerning...Heavy rainfall...Flash flooding possible Valid 272040Z - 280240Z SUMMARY...Potent thunderstorms in an environment with a rich moisture source present may produce flash flooding, especially in areas with overly saturated soils. DISCUSSION...Doppler Radar and GOES-16 satellite imagery identified a growing field of strong, to even severe, thunderstorms tracking from northeast WY and southwest MT into western SD. At the surface, a trough was denoted on surface observations that stretched into central ND. At mid-upper levels, a 500mb vorticity maximum was located over eastern WY and tracking ENE towards the heart of the Dakotas. RAP mesoanalysis showed up to 1.0-1.2" PWATs available, but as storms track east, RAP forecasts suggest PWATs may rise as high as 1.5" late afternoon in the central Dakotas. These values are above the 90th climatological percentile according to NAEFS. 18Z RAP forecast soundings between 20-00z suggested low-mid level RH values may average 90% and warm cloud layers as deep as 10,000ft. The exceptionally moist environment also coincides within an increasingly unstable atmosphere. RAP forecasts within the highlighted region indicate MLCAPE will likely average between 1,000-1,500 J/kg with this instability also in the form of a classic "skinny CAPE" profile on RAP model soundings. One other factor supporting heavy rainfall rates is vertical wind shear. Effective bulk shear will reach as high as 40 knots in eastern WY and northern SD, with sfc-3km SRH >200 m2/s2. These parameters will support mesocyclone development, which can be exceptional rainfall producers. Storm motions look to remain rather progressive, which should limit the areal extent and severity of possible flash flooding. That said, soils remain exceptionally saturated throughout the region. According to AHPS, much of southwest ND, northwest SD, southeast MT, and eastern WY have received as much as 300-400% of normal rainfall over the past 7 days. 1-hr FFGs are as low as 1" for much of western SD and southwest ND, which is plenty low enough for storms that could produce rainfall rates as high as 2"/hr. The areas that have witnessed the heaviest rainfall over the past week are the most susceptible to possible flash flooding this afternoon and evening. Poor drainage areas and urbanized communities are also at a heightened risk for possible flash flooding. Mullinax ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!7qS4egxeQx6Av1io5-3DRedZTC5fATGQK2_-puL_hiaBClAp2ULUgfhyEGZsfNs5dCeB= 89sKX-lqwTPxEVNbtxkrcZ4$ for graphic product... ATTN...WFO...ABR...BIS...BYZ...UNR... ATTN...RFC...MBRFC...NWC... LAT...LON 47230043 47189908 46519845 45269807 44160017=20 43810364 44140488 44810522 45480498 46220391=20 46860218=20 =3D =3D =3D To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .