Mesoscale Precipitation Discussion 1241
NWS Weather Prediction Center College Park MD
609 PM EST Sat Nov 22 2025

Areas affected...portions of central and southeast AZ

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

Valid 222258Z - 230458Z

Summary...Convection continues to grow in coverage across portions
of central and southeast AZ.  Hourly rain amounts up to 1" with
local amounts to 2" could lead to isolated to widely scattered
issues in arroyos/dry washes, burn scars, and box canyons.

Discussion...Infrared satellite imagery shows cooling cloud tops
in association with showers and thunderstorms across central and
southeast AZ within a region of 700 hPa confluence ahead of a
progressive deep layer low, with some recent uptick in coverage. 
A first pixels of 0.5" an hour amounts were indicated recently
from the Phoenix and Tucson AZ radars in association with their
rainfall.  Pockets of 500+ J/kg of MU CAPE exist across
west-central and southeast AZ per SPC mesoanalyses, with
instability increasing due to cooling aloft and some degree of
daytime heating/sunshine, particularly across southeast AZ. 
Effective bulk shear of 30-50 kts exists here, which is leading to
an environment with both organized and ordinary convective cells,
with the organized activity edging east of due north while the
less organized storms move just west of due north.  Precipitable
water values of 0.5-1" lie here.  The atmosphere is cool, with
1000-500 hPa thickness values of 5550-5600 meters.  When combined
with the available moisture, the column is approaching saturation.

The mesoscale guidance implies increasing convective coverage and
an increasing incidence of 0.5"+ an hour amounts over the next
several hours, with the 12z REFS and 18z HREF guidance suggesting
the heaviest rainfall in the 01-05z time frame.  This could be due
to cell training, occasional mesocyclone formation, or cell
mergers between more and less organized convective activity.  As
the upper level system continues marching northeast, winds should
veer somewhat which should allow convection to shift somewhat to
the east with time, with activity shifting increasingly into
mountainous areas.  With hourly amounts to 1" and local totals to
2" possible, the incidence of impactful heavy rain is expected to
be isolated to widely scattered, mainly within arroyos/dry washes,
box canyons, and any area burn scars.

Roth

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

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

LAT...LON   34911210 34811085 33170939 31640956 31201086
            32061186 34001212