Mesoscale Precipitation Discussion 0356
NWS Weather Prediction Center College Park MD
206 AM EDT Wed Jun 04 2025

Areas affected...southern/desert CA into western AZ

Concerning...Heavy rainfall...Flash flooding possible

Valid 040605Z - 041030Z

Summary...Localized high rainfall rates may continue to produce a
few areas of flash flooding from the desert regions of southern CA
into portions of western AZ through 10Z. Peak rainfall rates of
0.5 to 1.0 inches in 15-30 minutes will be possible.

Discussion...Regional radar imagery and GOES West infrared
satellite imagery through 0545Z showed scattered thunderstorms
continued from the desert regions of southern CA into the
southwestern edge of the Colorado Plateau through western AZ.
While cloud tops were warming overall, some new cell development
was noted near an outflow boundary pressing south through
southeastern San Bernardino and eastern Riverside counties along
with a few new cells showing up in Imperial County. Meanwhile in
AZ, showers/thunderstorms have been slowly edging south atop a
southward sagging outflow boundary which extended from northern
Gila County, westward into La Paz County. Many of these cells in
AZ have lost their vigor, but locally heavy rain continued in a
couple of spots. Although instability was lowering, SPC
mesoanalysis data showed these cells were occurring within 500 to
1000 J/kg MLCAPE and anomalous PWs of 1 to 1.5 inches.

A 700-500 mb upper low was centered just west of the northern Baja
Peninsula and is forecast to slowly track eastward along with a
northward extending trough. At least an isolated flash flood
threat will remain with development along outflow, and while cells
should be short-lived, there will be potential for peak rainfall
rates of 0.5 to 1 inch in 15-30 minutes. Despite nocturnal cooling
of the boundary layer, steep low to mid-level lapse rates will
continue to support weak CAPE values overnight and increasing low
level moisture with some return low level flow from the northern
Gulf of California...out ahead of the 700-500 mb low...may support
localized increases in CAPE over the next few hours, especially
across portions of western AZ. Therefore, for the next 4-5 hours,
a localized flash flood threat is expected to continue for
portions of southeastern CA into western AZ.

Otto

ATTN...WFO...FGZ...PSR...SGX...VEF...

ATTN...RFC...RSA...STR...NWC...

LAT...LON   35441214 35371122 35081078 34651074 34161111
            34001147 33561273 33161377 32661434 32541507
            32491587 32611633 33021654 33601658 34081605
            34611531 35041382