Mesoscale Precipitation Discussion 0750
NWS Weather Prediction Center College Park MD
813 PM EDT Fri Jul 18 2025

Areas affected...Southern NV...Central to Southwest UT...Northwest
AZ

Concerning...Heavy rainfall...Flash flooding likely

Valid 190013Z - 190600Z

SUMMARY...Scattered clusters of heavy showers and thunderstorms
will continue through the evening hours across portions of
southern NV, southwest to central UT and northwest AZ. Additional
localized areas of flash flooding will be likely near these storms
which will include potential slot canyon, dry wash and burn scar
flash flooding impacts.

DISCUSSION...The late-day GOES-W visible satellite imagery along
with radar data shows scattered clusters of heavy showers and
thunderstorms impacting areas of southern NV through southwest to
central UT and northwest AZ. The convection continues to evolve
within a moist and unstable airmass characterized by SBCAPE values
of 500 to 1000 J/kg, and PWs locally as high as 1.25 inches.

Generally the greatest instability and moisture concentrations are
over southern NV, and this is also where there is close proximity
of a well-defined mid-level vort center which is drifting near the
CA/NV border. A combination of this energy and the nearby
lingering moisture and instability should tend to maintain a
threat for heavy showers and thunderstorms going through the
remainder of the evening hours.

A look at the latest hires model guidance would suggest the
greatest threat for this additional convection will be mainly
confined to southern NV and portions of southwest to central UT.
This is where radar and satellite trends show multiple outflow
boundaries in close proximity to each other, which will likely
tend to interact with the remaining instability in a sufficient
way to facilitate additional convection over the next several
hours. Outflow boundary collisions and interaction with some of
the higher terrain will further enhance this threat.

Rainfall rates will be capable of reaching 1.0 to 1.5 inches/hour
with a lot of these rains falling in as little as 30 minutes where
the stronger convective cores set up. Additional rainfall totals
this evening may locally exceed 2.0 to 2.5 inches where any cells
become more focused near areas of higher terrain, and especially
in southwest UT.

Additional areas of flash flooding appear likely based on the
latest satellite and radar trends, and this will include concerns
for impacts to the normally dry washes, local slot canyon areas
and any burn scar locations.

Orrison

ATTN...WFO...FGZ...LKN...SLC...VEF...

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

LAT...LON   40431231 40071089 38931093 37271195 35901192
            35301252 35231381 36031557 37201720 38161716
            38481604 39201417