Mesoscale Precipitation Discussion 1484
NWS Weather Prediction Center College Park MD
755 AM EDT Mon Oct 12 2026
Areas affected...Western and Northern AZ...Southern UT
Concerning...Heavy rainfall...Flash flooding possible
Valid 121155Z - 121755Z
SUMMARY...An increase in showers and some thunderstorm activity
may result in some additional areas of flash flooding going
through the morning hours.
DISCUSSION...Radar and satellite imagery shows a gradual uptick in
the coverage of shower activity across areas of western and
northern AZ in association with an ejecting shortwave trough that
is seen lifting northeastward toward the region ahead of a deeper
layer trough farther to the west.
This energy and proximity of a cold front are working in tandem
with a nose of modest instability to facilitate the convective
development. MUCAPE values are locally near 500 J/kg, and the
latest OSPO ALPW data shows a relatively focused channel of
moisture in the 850/700 mb cloud-bearing layer to promote some
relatively efficient convection for locally heavy rainfall rates.
The latest HRRR guidance and the 06Z HREF suite suggest some
additional expansion of showers and perhaps a few thunderstorms
going through the morning hours as the shortwave energy lifts
across the region. DPVA associated with this along with orographic
ascent over areas of higher terrain will support some localized
enhancement of the convection.
Some spotty 1+ inch/hour rainfall rates will be possible over the
next several hours, and especially across northwest AZ. The latest
hires CAMs suggest some localized swaths of up to 2 inches of rain
being possible where some brief cell-training occurs. Given these
additional rains and the sensitive antecedent conditions on the
ground, some additional areas of flash flooding will be possible.
Some of the slot canyon and burn scar locations will be at
greatest risk for impacts.