515
AWUS01 KWNH 132307
FFGMPD
NMZ000-AZZ000-UTZ000-140405-

Mesoscale Precipitation Discussion 1276
NWS Weather Prediction Center College Park MD
706 PM EDT Sun Sep 13 2026

Areas affected...Southern UT...Much of AZ

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

Valid 132305Z - 140405Z

SUMMARY...Scattered areas of showers and thunderstorms will
continue into the evening hours across areas of southern UT down
through most of AZ. Some additional isolated areas of flash
flooding will be possible for the normally dry washes, burn scars
and slot canyon areas.

DISCUSSION...The latest GOES-W IR satellite imagery continues to
show mainly scattered areas of cold-topped shower and thunderstorm
activity across the Southwest U.S. with some of the better focus
of this convection situated across southern UT and northern AZ,
and to some extent portions of central to southeast AZ.

SBCAPE values remain rather high with values of 1500 to 2500 J/kg
in place. This coupled with the rather anomalous PW environment
with values as high as 2 to 3+ standard deviations above normal
will continue to support the stronger thunderstorms producing
rainfall rates as high as 1.5 inches/hour.

The ongoing activity is largely being driven by the diurnal
heating cycle with the aid of orographics and some localized
outflow/mesoscale boundary collisions. Given the favorable
thermodynamic environment that is in place, the threat of
scattered heavy showers and thunderstorms should continue for at
least a few more hours before sufficient convective overturning
and boundary layer cooling takes place to weaken the instability
profiles.

Some additional spotty 2+ inch rainfall totals cannot be ruled out
with the current cold-topped convection and especially where some
of these cells tend to be slow-moving and anchored near areas of
higher terrain. This will support an additional threat of isolated
flash flooding for a few more hours as a result. The normally dry
washes, burn scars, and slot canyons will remain at risk of seeing
these impacts including areas well removed and downstream from
where the heaviest rainfall has actually occurred.

Orrison

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

ATTN...WFO...ABQ...EPZ...FGZ...GJT...PSR...SLC...TWC...VEF...

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

LAT...LON   38211039 37950986 37140945 35720950 34820916
            33850890 33030885 32090885 31350921 31101019
            31381145 32021220 33171248 33951271 34691337
            35801357 36941322 37641239 38131132