364
AWUS01 KWNH 100334
FFGMPD
AZZ000-CAZ000-100800-

Mesoscale Precipitation Discussion 0992
NWS Weather Prediction Center College Park MD
1133 PM EDT Sun Aug 09 2026

Areas affected...Southern Arizona

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

Valid 100330Z - 100800Z

Summary...Clusters of thunderstorms will continue to progress
westward across southern Arizona the next few hours. Hourly
rainfall of 0.75 to 1.25 inches is possible, leading to isolated
instances of flash flooding.

Discussion...GOES-E IR satellite imagery this evening indicates
that cloud tops are continuing to rapidly cool across southern
Arizona. This cloud top cooling is associated with deepening
thunderstorms moving steadily east to west across the region. At
500mb, a shortwave trough is noted pushing west beneath the
monsoon ridge, driving locally enhanced forcing for ascent. This
lift, combined with surface convergence along boundary collisions
and storm mergers from the ongoing convection is producing renewed
thunderstorm activity thanks to impressive thermodynamics
characterized by PWs as high as 1.6 inches and MLCAPE 1500-2500
J/kg.

Recent MRMS hourly rainfall has been above 1 inch in a few of the
deeper convective cores, and despite limited signal in the HREF
neighborhood probabilities (just 5-15%), the ingredients suggest
these rates can continue for a few more hours. This is supported,
at least, by recent UA WRF and sub-hourly HRRR guidance as well.
As the shortwave pushes steadily to the west, it will impinge upon
thermodynamics that may additionally improve due to persistent
inflow off the Gulf of California. The overlap of the approaching
shortwave with an even more moist column suggests rainfall rates
of 0.75-1.25"/hr are likely. Limiting the total rain from this
convection is the speed at which these storms should move, as
propagation vectors are to the west at 20-25 kts, but any
collisions or redevelopment immediately downstream of the
mid-level wave could cause locally slower storm motions, or
repeating events. Where this occurs, 1-2" of rain is possible in
isolated locations.

In general, the modest storm coverage combined with steady storm
motions should preclude widespread flash flooding tonight.
However, any of these intense rain rates that move over vulnerable
terrain features like dry washes or burn scars, could lead to
flash flooding impacts before activity wanes later tonight.


Weiss

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

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

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

LAT...LON   33881303 33541207 32961106 32811080 32090998
            31731017 31461103 31371180 31781312 32391484
            33411461 33861410