Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu May 25 2023 19:35:21 AWUS01 KWNH 251935 FFGMPD MTZ000-WYZ000-UTZ000-IDZ000-NVZ000-CAZ000-ORZ000-260134- Mesoscale Precipitation Discussion 0336 NWS Weather Prediction Center College Park MD 334 PM EDT Thu May 25 2023 Areas affected...Great Basin Concerning...Heavy rainfall...Flash flooding possible Valid 251934Z - 260134Z Summary...Thunderstorms are beginning to initiate beneath the base of an elongated upper-low over the Great Basin. A combination of slow storm motions, some training, and rainfall rates up to 1"/hour could lead to instances of flash flooding this afternoon. Discussion...Visible satellite and 5 minute GLM data highlight increasing thunderstorm coverage and intensity over the last hour or so across parts of the Great Basin beneath an elongated upper-low with embedded vorticity maxima. This activity is tied to strong insolation with steep lapse rates aloft beneath the trough axis, with 500-1000 J/kg MUCAPE noted across northeast NV into MT. Strengthening left-exit forcing was also noted across the area as a subtropical jet streak rounds the base of the trough toward the Four Corners. Although some of the anomalous Eastern Pacific moisture has been scoured from the area compared to yesterday, PWATs of .4-.75" are lingering across much of the Great Basin, which is around the 75th percentile for this area compared to climatology. East of the vorticity maxima, stronger southwesterly flow aloft is also supporting effective some organized shear profiles with 25-30 kts effective shear depicted across UT, ID, and MT per SPC mesoanalysis. Over the next several hours, thunderstorms are expected to increase in coverage along and beneath the upper-trough axis. In NV, weak steering flow close to the vort max will lead to slow storm motions of 5-10 kts which will lengthen residence times of rainfall rates up to 1"/hour. Runoff could be augmented by high rain rates atop residual snowpack in elevated areas. Further northeast across ID, UT, and MT, northeasterly mean winds of 15-20 knots will enable slightly more progressive storm motions, albeit oriented parallel to the upper-forcing to support training segments. By 0Z tonight the 12Z HREF suggests elevated (20-50%) chances of QPF exceeding the 10 year ARI across the highlighted area, with a spotty signal for 100 year ARI exceedance (5-20%) also noted across northwest NV and southwest MT. This suggests flash flooding is possible through tonight, particularly atop burn scar areas and residual snowpack. ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!6WELItiZkW5kTOBwyAhk9-WY7pdiuzSb5dM4XLLdlN_E44Dd3WZgc5Nv6Ly6LnGCyZWq= DUr_99GbEtkJhuwvtyJHwhY$ for graphic product... ATTN...WFO...BOI...BYZ...LKN...MFR...MSO...PIH...REV...RIW... SLC...TFX...VEF... ATTN...RFC...CBRFC...CNRFC...MBRFC...NWRFC...NWC... LAT...LON 47220989 46340839 44610844 42901029 41271355=20 39771559 38291686 37761861 39292021 41062125=20 42031998 42471789 43241626 45391475 46551336=20 47181154=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) .