Mesoscale Precipitation Discussion 0622
NWS Weather Prediction Center College Park MD
1025 PM EDT Thu Aug 09 2018

Areas affected...central to southern AZ

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

Valid 100222Z - 100715Z

Summary...Flash flooding will be possible across portions of
central to southeastern AZ into the overnight hours. Rain rates of
1 inch or greater in 60 minutes or less from cell mergers will
likely continue for at least another few hours.

Discussion...Infrared and fading visible imagery from GOES-16
satellite showed scattered thunderstorms dropping south off of the
Mogollon Rim in central AZ at 02Z, with a combined outflow
boundary moving south into the lower elevations of south-central
AZ. Mostly clear skies during the middle and late afternoon over
southeastern AZ had allowed a local maximum in instability to
develop over portions of southeastern AZ with 00Z RAOBs from
Phoenix and Tucson indicating 1000-1500 J/kg MLCAPE and little
CIN. Moisture is greater as one moves from east to west, with
standardized precipitable water anomalies ranging from 1.5 to 2.5
across southern AZ.

0-6 km bulk shear is slightly higher over south-central AZ at
20-30 kt and given cloud bearing layer mean winds are generally
from the northeast at 10 kt or less, storms are expected to
persist with an overall movement into the lingering instability
axis over the next few hours. While cell movement is expected to
continue toward the south and west, local hang ups of heavy
rainfall cores and cell mergers will be sufficient to produce
rainfall rates of 1 inch or greater in 60 minutes or less time.
These rates could cause flash flooding in a few locations, with
lingering instability expected to continue convection for several
more hours.

Otto

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

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

LAT...LON   34431374 34401327 34271253 33921164 33531061
            33161020 32571006 31971025 31601121 31941251
            32671336 33291396 33871414