MESOSCALE PRECIPITATION DISCUSSION 0247
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
339 PM EDT SUN AUG 03 2014
 
AREAS AFFECTED...DESERT SOUTHWEST 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 031938Z - 040138Z
 
SUMMARY...THUNDERSTORMS WITHIN AN ENHANCED MONSOON REGIME NEAR AND
IN ADVANCE OF AN UPPER LEVEL LOW SHOULD CONTINUE INTO THE EVENING
HOURS. HOURLY RAIN RATES UP TO 1.75" ARE POSSIBLE, WHICH COULD
CAUSE FLASH FLOODING/DEBRIS FLOWS.

DISCUSSION...THE LATEST SPC MESOANALYSIS SHOWS A REGION OF >1000
J/KG MIXED LAYER CAPES ACROSS SOUTHERN NV, SOUTHERN CA, AND
PORTIONS OF SOUTHERN AND WESTERN AZ NEAR AND IN ADVANCE OF AN
UPPER-LEVEL LOW.  PRECIPITABLE WATER VALUES IN THE REGION ARE
1.50-2", WHICH ARE AROUND THREE SIGMAS ABOVE AVERAGE, OR ABOVE THE
95TH PERCENTILE FOR EARLY AUGUST.  LOW-LEVEL FLOW, PARTICULARLY AT
700 HPA, OF 15-20 KTS IS SEEN ACROSS AZ AND SOUTHERN UT, WHICH
COULD ORGANIZE ONGOING CONVECTION.

MOISTURE AVAILABILITY SHOULD ALLOW FOR HOURLY RAIN RATES UP TO
1.75", WITH LOCAL AMOUNTS OF 2-3" POSSIBLE WHERE CELLS
MERGE/TRAIN.  THE MEAN 850-400 HPA FLOW AND FORWARD PROPAGATING
CORFIDI VECTORS INDICATE NORTHWARD CELL MOTION OF 15-20 KTS IS
EXPECTED.  THE STRONGEST SIGNAL IN THE 12Z SSEO MEAN NEIGHBORHOOD
PROBABILITIES FOR EXCEEDING FLASH FLOOD GUIDANCE -- ABOVE 50% --
LIE IN THE MOUNTAINS EAST OF SAN DIEGO AND LOS ANGELES, WITH AREAS
OF WESTERN AZ, SOUTHWEST UT, AND SOUTHERN NV SHOWING >30% CHANCE
OF FFG EXCEEDANCE (AREAS WHERE THE MESOSCALE GUIDANCE TENDS TOO
SHOW TOO LITTLE THUNDERSTORM ACTIVITY).  FLASH FLOODING/DEBRIS
FLOWS ARE POSSIBLE IN THIS REGION.

ROTH

ATTN...WFO...GJT...TWC...FGZ...SLC...PSR...VEF...LKN...SGX...
REV...HNX...LOX...

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

LAT...LON   33271689 33801721 33701737 33421740 33881781 34131755
            34461838 35211889 36081866 37381921 38031797 38491513
            38551208 37881063 36271077 34281170 32141313 32011343
            32251426 32401476 32501488 32641488 32601558 32551652
            32611665 33271689