MESOSCALE PRECIPITATION DISCUSSION 0245
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
937 PM EDT SAT AUG 02 2014
 
AREAS AFFECTED...PORTIONS OF THE DESERT SOUTHWEST 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 030136Z - 030436Z
 
SUMMARY...A CONGEALING THUNDERSTORM COMPLEX ACROSS SOUTH-CENTRAL
AND SOUTHWEST AZ COULD LEAD TO HOURLY RAIN RATES UP TO 1.75",
WHICH COULD CAUSE FLASH FLOODING AND DEBRIS FLOWS.

DISCUSSION...THUNDERSTORMS ACROSS AZ HAVE BEEN INCREASING IN
COVERAGE OVER THE PAST SEVERAL HOURS.  THERE IS A WELL-DEFINED
OUTFLOW BOUNDARY ACROSS SOUTHERN AND WESTERN AZ PER THE 01Z
SURFACE OBSERVATIONS.  ALTHOUGH CONVECTION HAS BEEN PUSHING
WEST-SOUTHWEST AT CLOSE TO 25 KTS, CELL MERGERS AND BRIEF PERIODS
OF TRAINING HAVE LED TO HEAVY RAINFALL AND FLASH FLOOD WARNINGS. 
AN OBSERVATION NORTHWEST OF SCOTTSDALE AZ REPORTED 0.58" IN 20
MINUTES.

WHILE THE BEST SIGNAL FOR RAINFALL WITHIN THE MESOSCALE GUIDANCE
ENDS SHORTLY, CONVECTIVE TRENDS AND MODEL REFLECTIVITY IMAGES FROM
THE 12Z SPC WRF AND 18Z NAM CONEST IMPLY ACTIVITY SHOULD CONTINUE
OVERNIGHT, WHICH FITS THE PERSISTENCE OF CONVECTIVE ACTIVITY FROM
LAST NIGHT.  HOWEVER, A POOL OF STABILITY NEAR YUMA AZ PER THE SPC
MESOANALYSIS HAS LED TO THE DEATH OF CONVECTION TRYING TO INVADE
YUMA FROM SOUTHWEST AZ AND NORTHWEST MX OVER THE PAST COUPLE
HOURS, WHICH MAY BLOCK A SIGNIFICANT PORTION OF THIS ACTIVITY FROM
INVADING SOUTHEAST CA AS A LONG-LIVED COMPLEX.  CHOSE A THREE HOUR
WINDOW AS A COURSE OF LEAST REGRET.  HOURLY RAIN RATES UP TO 1.75"
AN HOUR WITH LOCAL AMOUNTS OF 2-3" COULD LEAD TO FLASH FLOODING IN
THIS REGION.

ROTH

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

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

LAT...LON   31201066 31241014 32440985 33321009 33801091 34021220
            34501297 34911331 36161343 36021406 35751478 35231565
            34561562 33861526 32701439 32021338 31571208 31471174
            31451164 31241083 31231080 31201066