AWUS01 KWNH 211258
FFGMPD
AZZ000-UTZ000-211830-

Mesoscale Precipitation Discussion 1505
NWS Weather Prediction Center College Park MD
857 AM EDT Wed Oct 21 2026

Areas affected...West-Central to Northern Arizona...Far Southern
Utah...

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

Valid 211300Z - 211830Z

SUMMARY...Favorable environment for back-building/repeating
thunderstorms continues through diurnal minimum in instability. 
Additional streak or two of 1-1.5" totals crossing areas having
received 1-2" continue to pose possible localized flash flooding
concerns through morning. 

DISCUSSION...GOES-W WV suite shows anomalous closed low off the SW
California Coast continues to slowly advance northeastward with
increasing dPVA throughout the southwest while the area of concern
downstream remains along the western edge of a confluent moist
warm conveyor belt emanating from the subtropical Eastern Pacific.

 CIRA LPW/LVT suite along with RAP analysis notes that slightly
veered surface to 850mb moist flow comes from the higher moisture
from the shallow/warm Gulf of California northward concurrent with
850-500mb layers coming more northward from a further south source
in the main ocean area south of Baja California.  Total PWats up
to 1.5 through the SW Deserts of Arizona spread northward with
1.2-1.3" spreading over the Mogollon Rim into the western San
Francisco Plateau.  Moderately unstable mid-levels support 1000
J/kg of MUCAPE along the interface of the sharp western gradient
of the moisture plume (and eastward) from the Colorado River
eastward.  

Aloft, the sub-tropical jet axis slowly turns anticyclonically in
proximity to Sun Valley into the southern SF Plateau providing a
broad area of diffluence aloft within stronger overall flow. 
Effective bulk shear over 50kts due to speed and low level veering
support organized low level convergence and eventually organized,
rotating updraft potential.   As such, the upwind edge across NW
Maricopa into Yavapai county has seen flanking redevelopment
through the morning with KIWA RADAR further hinting upstream
weaker returns indicative of higher elevated TCu/castellaus that
has not tapped lower level moisture convergence/instability but
has the upper-level dynamics to support those updrafts.  As such,
expectation is further development through the morning even in the
diurnal minimum of instability.

Given the overall moisture/convergence especially if updrafts are
rotating (like those currently in the vicinity of Flagstaff) may
support 1-1.5"/hr rates.   Deep layer stronger flow, cell motions
are quick even with slightly slowing due to rotating updrafts,
local duration will limit overall totals.  As such, it is required
for repeating tracks to result in localized 1-1.5" totals to
support potential localized flash flooding concerns.  However,
given the placement of the upper-level support and slow change
appear to be probable through the morning.  Additionally, expected
tracks may cross those that have received 1"+ localized totals
already this morning further helping the possibility for isolated
to widely scattered possible incident(s) of flash flooding.

Gallina

ATTN...WFO...FGZ...GJT...PSR...SLC...VEF...

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

LAT...LON   37841088 37650982 36820949 36050983 34801092 
            33851231 33591341 34151369 35471347 36801290 
            37651195 

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