Mesoscale Precipitation Discussion 0911
NWS Weather Prediction Center College Park MD
347 AM EDT Mon Oct 01 2018

Areas affected...Southern AZ...Far Southeast CA

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

Valid 010747Z - 011347Z

Summary...Slow moving convection drifting northward in a very
anomalous moist airmass poses a localized flash flood threat
through the morning hours.

Discussion...Recent radar returns from KYUX has shown an uptick in
reflectivity mainly along and south of the Arizona/Mexico border.
A recent RAP mesoanalysis still points to a pool of SBCAPE of
around 500 to locally 1000 J/kg across southern AZ and extreme
southeast CA. This is where isolated to scattered clusters of
storms have continued through the evening.

With favorable divergence aloft in the right entrance region of
the mid/upper level jet and highly anomalous moisture
characterized by PWATs of 1.7 to near 2.0" (per GPS TBW)
continuing to push north, convection will become increasingly
capable of producing intense rainfall rates exceeding 1 to 1.5
inches per hour. In addition, the latest run of the RAP suggests
the flow at 700 mb will increase in the next few hours from around
15 kts to 25 kts, supporting more efficient rainfall processes.
This rainfall occurring over the desert SW and its low FFGs
supports the flash flood threat.

Latest runs of the HRRR show a steady northward drift in the
showers and storms with expansion in coverage possible toward
10-12z. A consensus of the hi-res models through the next 6 hours
favors southern into south-central AZ as seen in the HREF
probabilities. Isoalted rainfall amounts of 1-2 inches will be
possible in the strongest, more persistent storms.

Taylor

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

ATTN...RFC...CBRFC...CNRFC...

LAT...LON   34781496 34361315 33101136 31731186 31541358
            31841489 32951550