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