800
AWUS01 KWNH 232334
FFGMPD
AZZ000-240515-

Mesoscale Precipitation Discussion 1118
NWS Weather Prediction Center College Park MD
734 PM EDT Sun Aug 23 2026

Areas affected...south-central to southern AZ

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

Valid 232333Z - 240515Z

Summary...Flash flooding will be possible across portions of
southern AZ through 05Z with at least isolated coverage. High
sub-hourly rain rates, locally exceeding 1 inch in 15 minutes, are
expected to lead to 1 to 2 inch totals (locally higher possible).

Discussion...Satellite and radar imagery showed a few ongoing
thunderstorms across the higher terrain of southeastern AZ as of
23Z with a general movement toward the west, though some cell
motions were slower than others. Additional attempts at convective
development were also noted over southern Maricopa/Pinal counties
in visible imagery while outflow was propagating southward off of
the Mogollon Rim across northern Maricopa County. The recent
increase in cell coverage has begun to form a couple of outflow
generated cold pools over southeastern AZ, with the potential
early stages of congealing occurring. Blended TPW imagery has
shown increasing moisture from the Gulf of CA into portions of
south-central and southwestern AZ since 12Z with values of 1.1 to
1.7 inches as of 22Z, helping contribute to MLCAPE of 500 to 2000
J/kg (highest over southwestern AZ as seen on the 23Z SPC
mesoanalysis).

Given the center of the mid to upper-level ridge was over
southeastern NM, an increased southerly trajectory to the low to
mid-level flow was seen into southern AZ. Expectations are for
continued convective development over the next couple of hours
over southeastern AZ (and possibly out ahead over south-central AZ
near/ahead of outflow), with movement around the ridge toward the
west and northwest. There is some uncertainty regarding convective
development over parts of southwestern AZ given increasing values
of convective inhibition with western extent as noted on SPC
mesoanalyses (Yuma County) but lift associated with outflow
propagation should be enough to overcome weaker values of
inhibition farther east (Pima and southern portions of Maricopa
and Pinal counties) if organization continues to increase. Should
at least a weakly organized convective cluster form, system
propagation should limit the duration of rainfall over any given
location. However, the environment will be supportive of high
sub-hourly rain rates similar to what has already been observed in
northern Santa Cruz County just after 22Z (1.38 inches in 15
minutes). 0.5 to 1.0+ inches in 15 minutes will be possible with
an evolution toward the west and northwest with time through 05Z,
possibly resulting in flash flooding of low water crossings,
normally dry washes and low lying areas.

Otto

...Please see www.wpc.ncep.noaa.gov for graphic product...

ATTN...WFO...PSR...TWC...

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

LAT...LON   33791258 33641153 32471025 31700998 31201023
            31561222 32091343 32761371 33151371 33671330