Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Nov 18 2025 19:04:59 AWUS01 KWNH 181904 FFGMPD AZZ000-NVZ000-CAZ000-190103- Mesoscale Precipitation Discussion 1232 NWS Weather Prediction Center College Park MD 203 PM EST Tue Nov 18 2025 Areas affected...Western Arizona, Southeast California and Southern Nevada Concerning...Heavy rainfall...Flash flooding likely Valid 181903Z - 190103Z SUMMARY...Flash flood risk increasing this afternoon into the evening across the Colorado River basin between southeast California, southern Nevada, and western Arizona. Heavy rainfall potential existing through sunset leading to potential night time flash flooding concerns. DISCUSSION...Current radar/IR satellite composite indicates a brief lull initiating over portions of southwest AZ and southeastern CA. Meanwhile, a steady progression of a stronger convective pulse over far northeast Baja will make headway to the north as it migrates within the broad deep layer steering flow out of the south-southwest. This is due to the proximity of the=20 persistent ULL presence off the southern CA coast with smaller shortwave perturbations emanating around the southern and eastern periphery of the upper-level circulation. Hi-res guidance, especially the last several HRRR iterations have been manifesting this very scenario of a brief lull, followed by the advection of the next stronger mid-level perturbation exiting out of Baja and shifting north along the adjacent Colorado River basin between AZ/CA/NV. This will coincide within a field of relatively buoyant air situated within the river basin, arcing back into southern NV along the warm/cold conveyor belt transition along the northern side of the surface low analyzed over the southern tip of NV. SBCAPE between 1000-1500 J/kg is analyzed across much of southwest AZ with an extension of 500-1000 J/kg located along the northern extent of the Colorado River basin between the three-state intersection. This setup is poised to advect further north with a greater SBCAPE alignment focused over the southern tip of NV down through far-southeast CA and much of western AZ. The combination of suitable vorticity advection and modest instability over an area of +2 to +3 sigma PWATs will assist in a re-invigoration of area convection with cells capable of 0.5-1.25"/hr at peak intensity, enough to favor some scattered flash flood prospects within the confines of northern Yuma, La Paz, Mojave counties in AZ, southern Clark county in NV, and far-eastern San Bernardino county in CA. Some training could occur with cells materializing on a north-south alignment for areas east of the Colorado River given the deep layer flow remaining fairly uni-directional. This could exacerbate flash flood concerns locally, leading to the threat running closer to the flash flooding likely prospect, especially within those western AZ counties. Kleebauer ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!9qZwoR-eYoOBPiD_vew7g_oNGgxGIH2VQ3sBHQQpMbB4o_gJuygnmXAcdPidULM-OuUA= grZKvmqIF-vCYVPBbaCFAgc$ for graphic product... ATTN...WFO...FGZ...PSR...VEF... ATTN...RFC...RSA...STR...NWC... LAT...LON 35831459 35801375 35291312 34391280 33221314=20 33161409 33711453 34251494 34881526 35531530=20 =20=20=20=20=20=20=20=20=20=20=20=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) .