Mesoscale Precipitation Discussion 0713
NWS Weather Prediction Center College Park MD
424 PM EDT Thu Aug 23 2018

Areas affected......Northern and Central Arizona...

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

Valid 232023Z - 240223Z

Summary...Convection forming over northern Arizona is expected to
continue through the afternoon. Slow cell movements could lead to
localized flash flooding in northern and central AZ.

Discussion...Showers and storms have formed over northern AZ in an
environment of above normal moisture.  The SPC mesoanalysis page
shows a plume of enhanced moisture advecting into the region, with
values increasing to 1.4-15 inches.  CAPE values of 1500 j/kg are
available. Lift has been generated by 300 mb divergence, and
upslope flow in the Mogollon Rim.

GFS forecast soundings in the region show light winds from the
surface to 600 mb, with the winds all 10 kt or less.  This will
result in slow motion, which enhances the threat of localized
flash flooding.

Most models indicate half to one inch of rain in the 6 hours
ending at 00z.  With flash flood guidance values indicating around
2 inches in 6 hours, the threat level is listed as possible with
so few members indicating heavier totals. The 18z version of the
NAM Conus Nest shows isolated maxima of 2-3 inches in the 6 hour
period, higher than prior runs.

Petersen

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

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

LAT...LON   36471256 36341213 36251145 35651045 35070992
            34000919 33741024 33601106 33701150 34121257
            34941332 35441352 35981352 36311312