Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Sep 28 2025 17:06:30 AWUS01 KWNH 281706 FFGMPD NMZ000-AZZ000-UTZ000-NVZ000-CAZ000-282305- Mesoscale Precipitation Discussion 1150 NWS Weather Prediction Center College Park MD 105 PM EDT Sun Sep 28 2025 Areas affected...Eastern CA...Southern NV...Far Southern UT...Northern and Western AZ Concerning...Heavy rainfall...Flash flooding possible Valid 281705Z - 282305Z SUMMARY...Locally heavy showers and thunderstorms will be developing and expanding in coverage going through the early to mid-afternoon hours. High rainfall rates and slow cell-motions may result in isolated to scattered areas of flash flooding by mid-afternoon. DISCUSSION...A mid to upper-level low is gradually beginning to lift off to the northeast across northwest AZ, and this energy coupled with daytime heating/increasing instability and orographics/upslope flow near areas of higher terrain will drive the development and expansion of locally heavy showers and thunderstorms going through the mid-afternoon hours. SBCAPE values are on the order of 1000 to 1500 J/kg southwest of the Mogollon Rim and to the south of the low center. However, visible satellite imagery shows strong diurnal heating taking place across these areas which will support a notable increase in instability over the next several hours. The strongest forcing associated with the low center and broader upper trough axis should be generally across areas of central and northern AZ going into the afternoon, and this is generally where the heaviest rainfall threat will tend to be from developing and expanding areas of convection. Proximity of the Mogollon Rim will further support a terrain-induced element to the convective threat. Scattered areas of convection will also be likely to develop up across far southern UT, southern NV and portions of eastern CA as differential heating boundaries become established and focus smaller scale forcing/focus for convective initiation. In fact, there is evidence of an MCV over southern NV which may foster a concern for locally more concentrated convection. PWs are anomalously high across northwest AZ and especially southern UT, southern NV and eastern CA where the anomalies are locally 2 to 2.5 standard deviations above normal. This will support convective cells with greater rainfall efficiency and thus elevated rainfall rates. Rainfall rates will should be capable of reaching up to 1.5 inches/hour with the stronger cells. Locally slow cell-motions with some concerns for terrain-anchored cells will facilitate the potential for some spotty 2 to 3+ inch rainfall totals. This may cause isolated to scattered areas of flash flooding which will include potential impacts to the area burn scar locations, slot canyons and arroyos. Orrison ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!8ErEAtlv0HYY17FTtPmEISsl5Jo4iq-iw6i8YScdnenXkZpH9JDmY0ji3LsNfBD81MZ-= zRbv5Nyr07voACSXIzaulqM$ for graphic product... ATTN...WFO...ABQ...FGZ...GJT...PSR...SLC...VEF... ATTN...RFC...RSA...STR...NWC... LAT...LON 37951141 37510970 36810894 35840904 35210969=20 34501040 33041225 33031402 33661475 34261528=20 34761586 35581634 36321635 36691611 37221524=20 37861332=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) .