Subj : Heavy Rain/Flood NV/CA/AZ To : All From : Mike Powell Date : Mon Jun 02 2025 07:25:00 AWUS01 KWNH 020850 FFGMPD AZZ000-NVZ000-CAZ000-021400- Mesoscale Precipitation Discussion 0343 NWS Weather Prediction Center College Park MD 449 AM EDT Mon Jun 02 2025 Areas affected...southern NV, eastern CA, northwestern AZ Concerning...Heavy rainfall...Flash flooding possible Valid 020848Z - 021400Z SUMMARY...A localized flash flood threat will set up for portions of western AZ, southern NV and far eastern CA over the next 4-5 hours. Slow moving cells will be capable of producing a quick 0.5 to perhaps 2 inches of rain. DISCUSSION...Over the past hour, GOES West infrared satellite and lightning imagery showed developing widely scattered showers and thunderstorms over western AZ. At 0830Z, a mid-level vorticity max was observed on GOES West water vapor imagery over central Mohave County, rotating WNW around a closed low centered to the south. While weak, CAPE has been on the rise as the closed low and its cold mid-level center, advance closer to the region with 08Z SPC mesoanalysis data showing roughly 500 J/kg MLCAPE from eastern CA into western AZ with slightly higher values of MUCAPE extending northward into southern NV. While a good portion of the area was estimated to be capped, CIN is weakening and surface dewpoints have been on the rise (5-10 F since 00Z) with 10-20 kt of southerly 850 mb flow up the Colorado Valley. Given northwest AZ's proximity to the closed low center, 850-300 mb mean layer winds are only 5-10 kt, indicative of the potential for very slow cell motions. Over the past 6-9 hours, layered PW imagery has shown a notable increase in moisture in the 850-500 mb layer, aiding in the recent expansion of instability. As convective inhibition continues to erode, additional cells are expected to form with the vorticity max and ahead of the closed upper low center in and around the tri-state region. The environment is supportive of small scale heavy rain cores which could produce roughly 0.5 inches of rain in 15-30 minutes, along with a spotty inch or two of accumulation. Overnight WoFS has been trending upward with rainfall potential and the 08Z cycle showed 40-50 percent probabilities for 1+ inches over southern NV and 30-40 percent to the east over central Coconino County. 90th percentile data (reasonable worst case scenario) indicated 2.3 inches of rain through 14Z. The expectation of a few heavy rainfall cores around the region could result in isolated areas flash flooding in low-lying or other areas of poor drainage. Otto ATTN...WFO...FGZ...PSR...VEF... ATTN...RFC...RSA...STR...NWC... LAT...LON 36671353 36481218 36131158 35501134 34281194 33771300 33761401 34041464 34501509 35291540 36061532 36601463 $$ --- SBBSecho 3.20-Linux * Origin: ILink: CCO - capitolcityonline.net (454:3/105) .