Mesoscale Precipitation Discussion 0708
NWS Weather Prediction Center College Park MD
201 PM EDT Wed Aug 22 2018

Areas affected......Northern Arizona and southern UT...

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

Valid 221735Z - 222335Z

Summary: Clusters of showers and storms developing in northwest AZ
and southern UT will increase in coverage this afternoon and lead
to localized flash flooding problems.

Discussion...Showers and thunderstorms will
continue to develop with destabilization over northwest AZ into
southern UT.  The region has favorable upper divergence and low
level convergence maxima located within an airmass with above
normal precipitable water values as high as 1.5-1.75 inches in
southern AZ per soundings from Yuma and Phoenix.

The confluent low to mid level flow and influx of low level
moisture from southern and central AZ has led to occasional back
building of activity in northwest AZ.
More activity is expected with additional destabilization in the
inflow axis plus upslope flow in the Mogollon Rim in AZ, with
activity then moving downstream into southern UT.

The NAM Conus Nest and 15z-16z High Res Rapid Refresh indicate 1-2
inches of rain are forecast this afternoon. Flash flood guidance
values are on the order of 1.5 inches in 3 hours, so it appears
guidance will be exceeded locally where the most persistent bands
are located.

With activity already having occurred in southwest UT, temporary
stabilization will limit the intensity of showers there.  the 15z
High Res Rapid Refresh indicates the area will destabilize later
this afternoon so addional activity may develop again.

Petersen




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

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

LAT...LON   37921059 37911003 37201020 36341102 35951149
            35531120 35211118 34751160 34391192 34451259
            35141329 35841384 36511376 37141297 37591210