Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu May 11 2023 19:11:45 AWUS01 KWNH 111911 FFGMPD SDZ000-NDZ000-MTZ000-120110- Mesoscale Precipitation Discussion 0264 NWS Weather Prediction Center College Park MD 311 PM EDT Thu May 11 2023 Areas affected...northern High Plains Concerning...Heavy rainfall...Flash flooding possible Valid 111910Z - 120110Z SUMMARY...Isolated flash flooding may occur across portions of the northern High Plains through the remainder of the afternoon into the evening. Localized 2 and 3 inch rainfall totals are expected with slow moving thunderstorms through 01Z. DISCUSSION...Through 1830Z, GOES East water vapor imagery showed a northern stream upper level trough moving across central MT with a DMV-derived jet max of 50-80 kt extending from north-central MT into Saskatchewan. At the surface, a quasi-stationary front was analyzed westward through ND before curling SSW through western SD and southeastern WY, through a weakly defined surface low in western SD. Low level easterly upslope flow was noted over the western Dakotas with flow backing to the NNE to the west of the frontal boundary. Low level moisture advection has supported PWATs near 1 inch across southeastern MT into southwestern ND and northwestern SD, but cloud cover over most of the region has limited insolation and MLCAPE was estimated by the 18Z SPC mesoanalysis to only be a few hundred J/kg across the western Dakotas. However, reduced cloud cover over west-central SD as seen on visible satellite imagery should allow further heating and increasing MLCAPE into the mid-afternoon. Further organization of an 850-700 mb low, identified in layered PW imagery over the tri-state region of MT/ND/SD, is expected to contribute to localized flash flooding in a couple of ways. First, strengthening low level flow around this low should enhance low level convergence to the north and west of the low over far eastern MT/far western ND, aiding in storm development. Second, Weak mean steering flow near the low-mid level low reflection in eastern MT should support slow movement of cells, with rainfall rates of 0.5 to 1 in/hr, granted through weak elevated instability of a couple hundred J/kg CAPE and added jet-induced divergence aloft. Better convective development/organization is anticipated from western SD into portions of southwestern ND given better instability/moisture profiles. Cell motions should be more progressive toward the north and northeast compared to those to the west, but also more efficient in rainfall production with potential for rainfall rates of 1-2 in/hr. Storm totals of 2-3 inches and flash flooding will be possible on an isolated basis, mostly over areas with low FFG or otherwise poorly draining surfaces. Otto ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!-AR6HsR3cEkXgAashoV51LOZlLhny_9jYlLuSee1fTnZgeEjGr34ZSJwsm1uiAY59pqU= HfWBxR9p8R3RAs9AjwCxBWc$ for graphic product... ATTN...WFO...ABR...BIS...BYZ...GGW...UNR... ATTN...RFC...MBRFC...NWC... LAT...LON 48050303 47730168 46510102 44720146 43960212=20 43840286 44110343 44770358 45210390 45370441=20 45560508 46320544 47630464=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) .