AWUS01 KWNH 291121
FFGMPD
NMZ000-AZZ000-291720-

Mesoscale Precipitation Discussion 1396
NWS Weather Prediction Center College Park MD
720 AM EDT Tue Sep 29 2026

Areas affected...Central and Southern AZ...Western NM

Concerning...Heavy rainfall...Flash flooding likely

Valid 291120Z - 291720Z

SUMMARY...Expanding showers and thunderstorms this morning with
high rainfall rates will likely result in areas of flash flooding.

DISCUSSION...The latest GOES-W IR/WV satellite imagery shows a
strong upper trough and associated closed low amplifying into the
Southwest U.S., with satellite showing cooling convective tops
across areas of central and southern AZ along with some portions
of western NM. Radar imagery confirms the uptick in convective
organization with areas of strong thunderstorm activity tending to
expanding in coverage while producing increasingly heavy rainfall rates.

Enhanced deep layer ascent/forcing associated with DPVA ahead of
the upper trough coupled with moist deeper layer southwest flow
ahead of it along with modest instability will support an
additional expansion of convection over the next several hours.
MUCAPE values are as high as 500 to 1000 J/kg, with PWs of 1.5 to
1.7 inches. The greatest combination of moisture and instability
is generally over southern AZ, and as the enhanced dynamics with
the amplifying upper trough arrive this morning, there should
rather well-organized bands or clusters of convection with high
rainfall rates.

PWs are in the 95th+ percentile of climatology, with well-defined
and poleward moisture contributions in the mid and upper-levels
emanating from Hurricane Polo that is crossing the Gulf of
California and preparing its second landfall into mainland Mexico.

The 06Z HREF/REFS guidance shows high 3-hour FFG exceedance
probabilities this morning as rainfall rates increase in
association with the uptick in convection. Some rainfall rates
will easily reach into the 1 to 2 inch/hour range, with potential
for some storm totals by late this morning of 2 to 4+ inches.
Areas of flash flooding will be likely as a result, and the
normally dry washes, burn scar locations and any box/slot canyon
areas will be particularly susceptible to impacts with potential
for enhanced runoff concerns. Some urban flooding impacts will
also be a concern at least locally.

Orrison

ATTN...WFO...ABQ...EPZ...FGZ...PSR...TWC...

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

LAT...LON   35640997 35560807 34870707 33990681 32670703 
            31670775 31180912 31191139 31651284 32071344 
            32881343 33951279 34771206 35301124 

$$
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