Mesoscale Precipitation Discussion 0712
NWS Weather Prediction Center College Park MD
127 PM EDT Thu Aug 23 2018

Areas affected......Southeast Arizona to Southwest NM...

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

Valid 231730Z - 232330Z

Summary...Convection expected to continue increasing in coverage
this afternoon in southeast Arizona to southwest NM, with a flash
flood threat from cell mergers and localized training.

Discussion...Regional radars indicated an increase in
showers/storms in southeast Arizona. The storms are developing in
an axis of 1500-2000 J/KG of MLCAPE in the 16z RAP mesoanalysis.
Upper level divergence on the periphery of the upper level ridge
is shown in the RAP analysis over the next several hours.

The storms are aligned with a moisture axis extending across
southern AZ with the 12z Tucson sounding showing deep moisture and
an estimated precipitable water of 1.78 inches, which is well
above normal.  The sounding showed no cap, so convection has
started early today.

The storms should move slowly northeast and localized cell mergers
and/or training should lead to local heavy rainfall amounts and
resultant flash flooding in areas with rapid runoff, like canyons,
urban locations, and burn scars.

The high res model runs have been indicating 1 to 3 inches of
rain, with the 16z High res rapid refresh showing one isolated
maxima to 4 inches.
The flash flood guidance is 1.5-2 inches in 3 hours, with should
be exceeded where extended thunderstorm activity occurs.

Petersen


ATTN...WFO...ABQ...EPZ...FGZ...PSR...TWC...

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

LAT...LON   33740999 33500796 32430805 31210836 30710942
            30941075 31841131 33051127