Mesoscale Precipitation Discussion 0550
NWS Weather Prediction Center College Park MD
403 PM EDT Sat Jul 28 2018

Areas affected...central/northern AZ

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

Valid 282002Z - 290115Z

SUMMARY...Scattered monsoonal convection will pose a flash flood
threat into the late afternoon/early evening over portions of
northern and central AZ. Rainfall rates of 1-2 inches over 60
minutes or less are expected in a few locations with possible
evolution into portions of central AZ near 00Z.

DISCUSSION...12Z analysis over AZ showed the greatest moisture
magnitude and departures from normal over southern portions of the
state but with weakly anomalous moisture into northern AZ and
southern NV (FGZ/VEF RAOBs). A 700-500 mb ridge was situated over
western AZ with somewhat weak/variable flow below 500 mb but with
a general movement of flow toward the south in the mid-levels over
the eastern half of the state. Visible satellite and regional
radar loops through 20Z indicated the development of diurnally
driven convection with slow moving or near stationary movement of
rain cores. The most notable of these was with a cell just north
of Flagstaff with radar estimated rates of 1-2 in/hr.

The concern for flash flooding comes from 14-day rainfall
departures from normal over portions of central and northern AZ
which may overlap with some of the slow moving convection which
will be capable of 1-2 inches in a 60 minute period or shorter.
VAD wind plots from KIWX AND TPHX showed 850 mb flow orthogonal to
the orientation of the Mogollon Rim which may help support added
low level convergence if convection is able to congeal and
propagate southward off of the Rim into some of the lower
elevations toward 00Z. While not expected to be widespread, flash
flooding appears possible over central/northern portions of AZ
through at least 01Z.

Otto

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

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

LAT...LON   36761282 36691227 36491172 36321141 35931101
            35441074 35061042 34731010 34390945 33890910
            33290921 33020979 32981049 33321208 33701296
            34401367 35451417 36281407 36751356