MESOSCALE PRECIPITATION DISCUSSION 0297
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
501 AM EDT TUE AUG 19 2014
 
AREAS AFFECTED...DESERT SOUTHWEST 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 190859Z - 191359Z
 
SUMMARY...THUNDERSTORMS HAVE BEEN DEVELOPING WITHIN THIS REGION AS
LOW-LEVEL INFLOW INCREASES WITHIN AN ENVIRONMENT OF AMPLE MOISTURE
AND INSTABILITY.  FLASH FLOODING AND ASSOCIATED DEBRIS FLOWS
REMAIN POSSIBLE.

DISCUSSION...OVER THE PAST COUPLE HOURS, CLOUD BASE INFLOW HAS
BEEN INCREASING ACROSS THE DESERT SOUTHWEST AS A DEEP-LAYERED
CYCLONE MOVES OFFSHORE THE CENTRAL CA COAST.  THUNDERSTORMS HAVE
BEEN DEVELOPING WITHIN THIS REGION, WHICH CONTAINS PRECIPITABLE
WATER VALUES OF 1-2", AROUND TWO SIGMAS ABOVE NORMAL.  MIXED LAYER
CAPE VALUES ACROSS WESTERN AZ AND SOUTHERN NV REMAIN 1000+ J/KG
WITHIN A REGION THAT SAW MINIMAL AFTERNOON THUNDERSTORM ACTIVITY.

THE EXPECTATION IS THAT THUNDERSTORMS SHOULD CONTINUE TO DEVELOP
AND ORGANIZE OVER THE NEXT SEVERAL HOURS.  THE 00Z SSEO
NEIGHBORHOOD PROBABILITIES SHOW A >50% CHANCE OF BREACHING THREE
HOURLY FLASH FLOOD VALUES NEAR THE WESTERN AZ/UT BORDER PAST
SUNRISE, WITH A >30% CHANCE ACROSS SOUTHERN AZ.  THE MESOSCALE
GUIDANCE HAS BEEN UNUSUALLY BULLISH ON QPF IN THIS REGION, WITH
LOCAL 2-4" AMOUNTS ADVERTISED.  HOURLY RAIN RATES OF 1-2" ARE
EXPECTED IN STRONGER THUNDERSTORMS, GIVEN THE AVAILABLE MOISTURE. 
THIS TYPE OF RAINFALL IN THE DESERT COULD CAUSE FLASH FLOODING AND
DEBRIS FLOWS.

ROTH

ATTN...WFO...FGZ...LKN...PSR...SLC...TWC...VEF...

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

LAT...LON   386311458 383111325 372911256 366711239 352111198 
            334211161 321211143 316611203 319211324 321411393 
            321411400 323811456 330911541 346011610 361811660 
            368911675 376611651 384111570