Mesoscale Precipitation Discussion 0710
NWS Weather Prediction Center College Park MD
434 PM EDT Wed Aug 22 2018

Areas affected......Southern AZ to Southwest NM...

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

Valid 222032Z - 230232Z

Summary...Clusters of showers and storms developing in Southern AZ
and southwest NM will continue this afternoon and evening and
might lead to localized flash flooding problems.

Discussion...Showers and thunderstorms have developed in portions
of southern Arizona in a moist airmass. With mid level southerly
flow the storms have shown a north slow motion.  The morning
Phoenix and Tucson soundings showed high available moisture with
precipitable water values of 1.5-1,75 inches. 

The region has favorable upper divergence  maxima forecast by the
16-18z High Res Rapid Refresh the rest of this afternoon into this
evening, which combines with the high available moisture and
merger of low level outflow boundaries to trigger additional
showers/storms.

The confluent low to mid level flow has led to occasional back
building of activity in southern AZ.  More activity is expected
with additional destabilization in the inflow axis plus upslope
flow in terrain in southern AZ over to western NM with activity
then moving downstream into adjacent valley areas.

The high resolution ensemble runs and 16z-18z High Res Rapid
Refresh indicate pockets of 1-2 inches of rain are forecast
through 03z. Flash flood guidance values are on the order of 1.5-2
inches in 3 hours, so it appears guidance will be exceeded locally
where the most persistent bands are located.

The 18z NAM Conus Nest has locally higher totals to 3 inches in
far southern AZ to the NM border, in response to slow moving
pockets of boundary layer moisture convergence, as low level winds
are weak.

Petersen




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

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

LAT...LON   35051115 35031064 34730959 34620875 34080810
            33140809 32300829 31560861 31120885 30610972
            30641054 31301164 31431168 31561176 31901210
            32601254 33061261 33391256 33821244 34171229
            34541202 34801180 34991162 35031140