Mesoscale Precipitation Discussion 1044
NWS Weather Prediction Center College Park MD
426 PM EDT Wed Sep 03 2025

Areas affected...much of northern AZ into southern NV and
southwest UT

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

Valid 032025Z - 040200Z

Summary...Sub-hourly (15-30 min) rainfall of 1"+ with short-term
totals of 1.5-2.5" may result in localized/isolated instances of
flash flooding.

Discussion...Complex upper-level pattern (slow moving
trough/closed low to the west with poleward advancement of
Hurricane Lorena to the south resulting in enhanced upper-level
diffluence in left-exit region of sub-tropical jet streak)
combined with anomalous tropospheric moisture content (at or near
90th percetile) is resulting in a favorable environment for heavy
rainfall across the greater AZ/NV/NM border region. Convection is
initiating and proliferating in the vicinity of the higher terrain
of the Mogollon Rim and Grand Canyon region (where the best low-
to mid-level moisture is overlapping with upper-level moisture,
per CIRA ALPW imagery). MRMS is indicating high instantaneous
rainfall rates (2"+/hr) with initial downdrafts, resulting in
sub-hourly (15-30 min) localized accumulations of 1"+.

As convection continues to proliferate and move relatively slowly
(~10 kts) towards the north-northwest with mean 850-300 mb flow,
cells may locally train to result in localized short-term totals
of 1.5-2.5" (supported by HREF and experimental RRFS neighborhood
probabilities for 1" and 2" exceedance). While these higher
localized totals are most likely in the vicinity of the higher
terrain, the influence of upper-level dynamics may be enough to
support updrafts beyond the typical pulse convection life cycle as
they drift northward. Isolated/localized instances of flash
flooding will be possible.

Churchill

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

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

LAT...LON   39121195 38381138 37911132 37491128 37211104
            37191067 37121031 36860999 36590964 36230947
            35730956 35590991 35591017 35411027 35161042
            34641028 34351048 34251099 34261152 34221195
            34251243 34481290 34871342 34901402 35371455
            35941515 36191566 36611588 37131599 37461630
            37221699 37851717 38411671 38341529 38781497
            38891414 38791283