Subj : Flood potential AZ To : All From : Mike Powell Date : Tue Nov 18 2025 09:03:54 AWUS01 KWNH 181228 FFGMPD AZZ000-CAZ000-181826- Mesoscale Precipitation Discussion 1231 NWS Weather Prediction Center College Park MD 727 AM EST Tue Nov 18 2025 Areas affected...portions of western AZ Concerning...Heavy rainfall...Flash flooding possible Valid 181226Z - 181826Z Summary...An area of heavy rain with embedded thunderstorms should continue across portions of western AZ over the next several hours. Hourly rain amounts to 1.5" and local 3" totals are possible, which would continue isolated to widely scattered flash flood concerns. Discussion...An upper level low is sliding southeast down the CA coast past Lompoc. It has led to a broad area of divergence aloft across the Southwest. Precipitable water values of 1"+ are indicated in RAP forecasts, with some GPS values across Las Vegas and Phoenix in the 0.8-0.9" range. When combined with 1000-500 hPa thickness values of 5550 meters, the atmosphere is saturated which has led to efficient heavy rainfall across portions of southwest AZ this morning, with radar indications of 1"+ in an hour at times. MU CAPE of 500-1000 J/kg exists downstream from the Gulf of CA northward across southwest AZ. Effective bulk shear of 25 kts is helping to organize the convective elements. A shortwave noted on water vapor imagery across southern CA could cause some backing of the low level flow in the short term, potentially shifting the heavy rain area somewhat westward with time. RAP guidance fields indicate expansion of the instability pool northeast with time, which could lead to some northeast shift. When taken together, the heavy rain footprint could broaden with time. Hourly rain amounts to 1.5" and local totals to 3" are possible where cells backbuild and train. Burn scar locations, arroyos/dry washes, box canyons, and urban areas should be most sensitive to this rainfall. Isolated to widely scattered flash flood concerns should continue into the day today. Roth $$ --- SBBSecho 3.28-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (618:250/1) .