Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu May 25 2023 20:42:25 AWUS01 KWNH 252042 FFGMPD SDZ000-NDZ000-MTZ000-WYZ000-260240- Mesoscale Precipitation Discussion 0337 NWS Weather Prediction Center College Park MD 441 PM EDT Thu May 25 2023 Areas affected...Northern WY...Central and Eastern MT Concerning...Heavy rainfall...Flash flooding possible Valid 252040Z - 260240Z SUMMARY...Showers and thunderstorms will be expanding in coverage over the next few hours and will impact areas of northern WY through central and eastern MT going through the late afternoon and early evening hours. Heavy rainfall rates of 1 to 1.5 inches/hour coupled with locally wet antecedent conditions may result in some runoff concerns and possible flash flooding. DISCUSSION...The latest surface analysis shows a quasi-stationary front draped from the Great Basin northeastward across the northern Rockies and across areas of southern MT with multiple waves of low pressure riding northeast along it. This is being facilitated at least in part by a broad upper trough over the western U.S. with multiple shortwave impulses rotating out of the base of it and up across the broader Intermountain West. Over the next few hours, some of this shortwave energy will be exiting the northern Rockies and crossing through areas of northern WY and into central and eastern MT. Relatively divergent flow aloft associated with modest DPVA will couple with a moderately unstable boundary layer characterized by MLCAPE values of 1000 to 1500 J/kg for convection to develop and expand in coverage. Already locally strong convection is seen in radar and GOES-W IR satellite imagery over areas of northwest WY and southwest MT in closer proximity to shortwave forcing and favorable orographics. PWs pooled up across central and eastern MT are anomalously high for this time of the year, with values as much as 2 standard deviations above normal. This moisture coupled with the elevated instability parameters should favor convection with rather high rainfall rates. The 12Z HREF guidance favors rates locally reaching 1 to 1.5 inches/hour with some spotty storm totals of as much as 2 to 3 inches where some brief repeating cell-activity occurs. The antecedent conditions are locally wet, with elevated streamflows noted, and this coupled with the high rainfall rates may result in there being some runoff concerns with isolated areas of flash flooding. Orrison ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!4E_6JPhUuduaaZraaMlqYBNrfJ4hy-blOqNX9gY0Fcxciabw-KEGJ-fl04FzLB7TpLhe= te8eHNF2HTZD3_TTvHolBCE$ for graphic product... ATTN...WFO...BIS...BYZ...GGW...RIW...TFX...UNR... ATTN...RFC...MBRFC...NWRFC...NWC... LAT...LON 48120647 47920493 47230404 46280383 45160419=20 44170551 43710701 43570821 43740990 44651103=20 45871114 47041007 47760862=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) .