Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Aug 22 2025 21:02:16 AWUS01 KWNH 222102 FFGMPD AZZ000-UTZ000-NVZ000-CAZ000-230300- Mesoscale Precipitation Discussion 0976 NWS Weather Prediction Center College Park MD 500 PM EDT Fri Aug 22 2025 Areas affected...Far Eastern CA...Southern NV...Central to Northwest AZ...Central and Southwest UT Concerning...Heavy rainfall...Flash flooding possible Valid 222100Z - 230300Z SUMMARY...Scattered monsoonal showers and thunderstorms are expected going through the afternoon and early evening hours across portions of the Southwest U.S. Some localized concerns for flash flooding will exist for the more sensitive slot canyon locations and burn scar areas. DISCUSSION...The early-afternoon GOES-W visible satellite imagery shows a substantial CU/TCU field over the Mogollon Rim of central to northwest AZ and also across much of southwest UT where a combination of orographics along with diurnally enhanced instability and the presence of monsoonal moisture are working to initiate additional areas of convection. Already there are scattered small-scale clusters of locally heavy showers and thunderstorms where differential boundaries and nearby terrain-induced circulations have been helping to initiate and locally concentrate pockets of convection. Early day cloud cover has locally helped to mitigate the level of surface-based instability, but satellite trends show substantial heating occurring over much of central to northwest AZ and into southwest UT which should help to facilitate additional scattered areas of showers and thunderstorms over the next several hours. There is also proximity of an MCV near the CA/AZ/NV border region, and differential heating along the eastern and northern flanks of this energy and associated cloud canopy may also help drive convective initiation this afternoon. The region is relatively moist today with PW anomalies coming in as high as 1.5 standard deviations above normal in close proximity to a 700 mb high center. CIRA-ALPW data generally shows some of the greater moisture concentrations in the 700/500 mb layer and this will help to support some relatively efficient convection for heavier rainfall rates. Some rainfall rates may reach as high as 1 inch in 20 to 30 minutes with the stronger cells, with some spotty rainfall totals through this evening reaching as high as 1.5 to 2.5 inches where any cells tend to become anchored near areas of higher terrain. Some of the RRFS/REFS guidance supports this which seems plausible given the satellite and radar trends. This may result in there being localized areas of flash flooding. There are some sensitive burn scar concerns (especially over northern AZ) along with the normally sensitive slot canyon locations (southwest to south-central UT) that are vulnerable to any high rainfall rate activity, so these areas should be closely monitored. Orrison ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!6YDKnBG52iNQy2dp4u55cuA3H6DEvnr6GvljAi0db6MzWMTR4mtzjPNmMZaJFgSeFft9= I8oOgLEK3VFG52FX71C-Dhc$ for graphic product... ATTN...WFO...FGZ...LKN...PSR...SLC...VEF... ATTN...RFC...RSA...STR...NWC... LAT...LON 39181115 39001068 37981065 36701168 35571155=20 34731061 34291023 33791048 33641127 33651273=20 33791397 34251523 35121602 36071625 36881610=20 37781544 38421455 38751351 38861244=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 3.28-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .