Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri May 26 2023 22:46:14 AWUS01 KWNH 262246 FFGMPD SDZ000-NDZ000-MTZ000-WYZ000-270445- Mesoscale Precipitation Discussion 0349 NWS Weather Prediction Center College Park MD 645 PM EDT Fri May 26 2023 Areas affected...Central/Northern WY...Southeast MT...Western ND...Far Northwest SD Concerning...Heavy rainfall...Flash flooding possible Valid 262245Z - 270445Z SUMMARY...Increasing coverage of heavy showers and thunderstorms with concerns for localized cell-mergers and training cell-activity should pose at least some flash flood threat going into the evening hours. DISCUSSION...Radar and satellite imagery shows multiple clusters of heavy showers and thunderstorms impacting areas of central and northern WY with coverage beginning to expand into far southeast MT and across western ND. The convection is being strongly driven by the arrival of a low-amplitude shortwave trough ejecting downstream from the much larger scale trough over the Great Basin. This energy is interacting interacting with a strongly unstable boundary layer with MLCAPE values of 2000+ J/kg pooled up across eastern WY and toward southeast MT. This is also with proximity of a quasi-stationary front where at least some weak transient surface wave activity is noted. PWs are anomalously high across the region and locally 2+ standard deviations above normal across eastern WY and into much of eastern MT and the western Dakotas. This coupled with the instability and a fair amount of low to mid-level shear will enhance the rainfall potential, with some rainfall rates of 1.5 to 2 inches/hour with the stronger storms. Already the hires models from the 12Z HREF suite appear largely slow with the convective evolution and underdone with their amounts. However, recent HRRR runs have been trending a bit wetter with their QPF signal for the evening hours. The expectation is that the convection over the next few hours will continue to grow upscale and especially up over areas of southeast MT. Adjacent areas of western ND and even far northwest SD near the Black Hills will also be a concern for areas of slow-moving and locally concentrated convection. Some pockets of cell-merger activity and cell-training will be possible. Rainfall amounts going through the evening hours are expected to locally reach 2 to 4 inches, with isolated heavier amounts to 5+ inches possible. Locally wet antecedent conditions and somewhat elevated streamflows in conjunction with these additional rains may facilitate some areas of flash flooding through this evening. Orrison ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!4_3nbXtwKObsaVmPyvk9kdbz6cmZR3mWCrzIHIzplj531VY1fM_S4-VySegCdsL_l2rr= YP20c5fmjYjK9KSHy2PXFCE$ for graphic product... ATTN...WFO...BIS...BYZ...CYS...GGW...RIW...UNR... ATTN...RFC...MBRFC...NWC... LAT...LON 48530262 48000181 46150336 44110387 43070456=20 42350574 42540823 43660901 44910875 46200747=20 47450539=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) .