Graphic for MPD #0978

Mesoscale Precipitation Discussion 0978
NWS Weather Prediction Center College Park MD
858 PM EDT Sat Oct 13 2018

Areas affected...Arizona

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

Valid 140057Z - 140615Z

Summary...Additional showers and thunderstorms capable of
producing heavy to possibly excessive rainfall will re-develop
over Arizona this evening in response to highly difluent flow
around a mid- and upper-level low. Localized rainfall rates of an
inch per hour possible which could lead to flash flooding.

Discussion...A well-defined mid-latitude cyclone was situated over
the Desert Southwest near the International Border.  in the
general vicinity of the Lower Colorado River Valley. The low
remains quite evident on GOES-16 water vapor imagery as was the
highly diffluent flow to the east.  This diffluent flow was
sustaining one area of rain over central Arizona which was moving
north and east.  This area appears to be moving out of the best
instability which should gradually lead to decreasing rainfall
rates.

However, additional convection has started to develop back near
the center of the upper level system where the combination of
colder mid/upper level temperatures and afternoon heating has
steepened lapse rates and resulted in Surface Based CAPE values in
excess of 1000 J per kg.  VWPs from the KIWA and TPHX radars
continue to show southeasterly low level flow feeding into the
area where convection has been growing early this evening.

The cumulative effect of persistent rain with occasionally heavy
rain bands looks to be enough to continue the risk of heavy to
possibly excessive rainfall over the Sonoran Desert region of
southern and southwest Arizona. Recent runs of the HRRR and the
RAP attempt to focus heaviest rainfall in this area with the RAP
indicating that the area of SB CAPE in excess of 1000 J per kg
moving east through the evening. 

Bann

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

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

LAT...LON   34541304 34231188 33701116 33241104 32671188
            32311281 32381432 33231516 33711448 34471404
           


Last Updated: 858 PM EDT Sat Oct 13 2018