Mesoscale Precipitation Discussion 0352
NWS Weather Prediction Center College Park MD
240 PM EDT Tue Jun 03 2025

Areas affected...Southern and Eastern CA...Southern NV...Northwest
AZ...Far Southwest UT

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

Valid 031840Z - 040040Z

SUMMARY...Scattered areas of showers and thunderstorms will
develop this afternoon across the broader Southwest U.S. which
will be capable of producing locally heavy rainfall. Given the
high rainfall rate potential, isolated to scattered areas of flash
flooding will be possible.

DISCUSSION...An anomalously moist airmass through the vertical
column has pooled across large areas of the Southwest U.S. with PW
anomalies that are near or at record levels for the date. This
coupled with strong diurnal heating/surface-based instability by
later this afternoon should result in a favorable environment for
showers and thunderstorms to initiate and gradually expand in
coverage.

An upper-level low is seen in WV satellite imagery dropping
southeastward offshore of southern CA, and this is yielding very
steep mid-level lapse rates along with divergent flow aloft around
its northeast flank which will further facilitate convective
development over the next several hours.

The steep mid-level lapse rates coupled with the boundary layer
heating should facilitate SBCAPE values reaching as high as 1000
to 2000 J/kg, with the greater CAPE fields likely focusing over
northwest AZ and far southern NV. A combination of favorable
thermodynamics along with localized orographics/terrain-induced
circulations and even some modest shear over the region should
yield scattered pulse to multi-cell thunderstorms which will be
capable of producing rainfall rates of up to 1.5 inches/hour, with
even some sub-hourly rates of 1 inch in 20 to 30 minutes possible.

A look at the latest HREF/REFS guidance suggests some potential
for 2 to 3+ inch rainfall totals where the storms become locally
anchored near some of the terrain, and where any potential
cell-merger activity occurs. This will allow for isolated to
scattered areas of flash flooding to be possible. Some of the area
burn scars will be at particular risk for impacts, along with dry
washes and local slot canyon areas.

Orrison

ATTN...WFO...FGZ...GJT...HNX...LOX...MTR...PSR...REV...SGX...
SLC...VEF...

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

LAT...LON   37651221 36921048 35121012 34211138 34271332
            34171475 33541551 32731573 32611686 33501754
            33991821 34441930 34672001 34892039 35482086
            35792094 36042033 35641929 35731865 36291858
            37401903 37631862 37011736 37561486