352
AWUS01 KWNH 301538
FFGMPD
AZZ000-UTZ000-NVZ000-CAZ000-302015-

Mesoscale Precipitation Discussion 1531
NWS Weather Prediction Center College Park MD
1137 AM EDT Fri Oct 30 2026

Areas affected...Lower Colorado River Valley into central AZ and
southwestern UT

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

Valid 301537Z - 302015Z

Summary...Localized flash flooding may occur across portions of
the Colorado River Valley into central AZ and southwestern UT
through 20Z. Peak hourly rainfall values over 1 inch are expected
within axes of repeating or training of heavy rain.

Discussion...15Z radar imagery showed scattered thunderstorms over
southern NV into southwestern UT and western AZ, located ahead of
a well-defined mid to upper-level trough advancing eastward into
southern CA as seen on water vapor imagery. A zonally oriented
upper level jet max was located just south of the upper trough
over the eastern Pacific with 130 kt sampled by GOES West DMVs.
Despite the morning time frame, instability via the 12Z VEF
sounding and 15Z SPC mesoanalysis showed a mixture of ML and MU
CAPE ranging from 500 to 1000+ J/kg (highest over southwestern
AZ). Regarding moisture, OSPO ALPW imagery showed the northward
moisture transport from the surface to 700 mb via 25-35 kt of
flow, aligned with the ongoing axis of storms over the Southwest.
Precipitable water values of about 1 inch in southern NV to 1.3
inches in southwestern/south-central AZ were estimated via the
latest GPS observations, representing standardized anomalies of 2
to 4.

Ascent ahead of the advancing upper trough will continue to
combine with the low level axis of moisture transport to maintain
thunderstorms through the day. RAP guidance shows some weakening
of the 850-700 mb flow into the afternoon but also instability
expanding with some degree of daytime heating through the cloud
cover. Southerly steering flow into the Mogollon Rim is expected
to provide one focus for heavier rainfall via orographic lift
through the mid-afternoon hours while the ongoing axis of storms
slowly advances east. Increasing upper level divergence and
diffluence are expected within the left exit region of the upper
level jet max into the lower CO River Valley into central AZ which
should aid broader scale lift. Instability will drop off with
northern extent but remain sufficient when combined with the upper
forcing and unidirectional flow to support repeating and training
of heavy rain into portions of southern NV and southwestern UT,
with instability lingering beyond 20Z. Peak hourly rainfall of 1
to 1.5 inches will be possible within the better zone of
instability across central to southern AZ, while peak hourly
values of 0.5 to 1.0 inches are expected to the north. High
sub-hourly rainfall values will help drive the flash flood threat
with burn scars and areas of sensitive terrain at most risk of
impacts.

Otto

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

ATTN...WFO...FGZ...PSR...SLC...TWC...VEF...

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

LAT...LON   39031356 38951241 36941184 35071120 34011092
            33061119 32751186 32751317 33291397 34861496
            35751527 37081516