Mesoscale Precipitation Discussion 0553
NWS Weather Prediction Center College Park MD
922 PM EDT Sat Jul 28 2018

Areas affected...Portions of central and northern Arizona

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

Valid 290120Z - 290520Z

SUMMARY...Scattered convection weakening over the next few hours
could still produce hourly rainfall rates over 1.50 inches, as the
convection moves out of the higher terrain toward the south and
southwest. This is expected to maintain the flash flood threat
through the evening hours.

DISCUSSION...Regional radars showed that the convection over the
Mogollon Rim may have peaked in coverage and intensity near
29/01z, as instability remains near 1000 J/KG MUCAPE (supported by
the 29/00z KFGZ sounding). Mean winds remain fairly weak
(generally under 10 knots from the north) as the activity remains
on the eastern side of the mid level ridge. Precipitable water
values remain near an inch, and the combination of high moisture
content air and slow cell motions has resulted in locally hourly
rainfall near 1.50 (based on the most recent KFGZ OHP product).

As is typical for convection across the Mogollon Rim near 00z, the
activity is starting to move out of the terrain and into the lower
elevations of central AZ, drifting with the weak 700 mb wind flow.
With little in the way of synoptic scale forcing, the motion of
the storms will continue to present the greatest flash flood
threat, until the instability is finally consumed, somewhere
between 29/03z and 29/06z. Heavy rainfall across the higher
terrain the past few nights has set the stage for wet soils, and
additional heavy rainfall will enhance the flash flood threat.

Much of the higher resolution guidance is not covering the current
threat well, so the placement of the heavy rainfall and flash
flood threat was based on trends on satellite and radar. Local
1.50 inch rainfall amounts could produce flash flooding. Given the
coverage of the convection, flash flooding is considered possible
at this time.

Hayes

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

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

LAT...LON   36281349 36251298 35971251 35071167 34261091
            33381014 32841024 32861071 33101135 33971271
            35001359 35971376