MESOSCALE PRECIPITATION DISCUSSION 0198
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1028 PM EDT SUN JUL 13 2014
 
AREAS AFFECTED...SOUTHERN AZ, SOUTHEAST CA, SOUTHERN NV 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 140227Z - 140827Z
 
SUMMARY...A MONSOON SURGE IS EXPECTED TO BRING LOCALLY HEAVY RAINS
TO THE DESERT SOUTHWEST OVERNIGHT.  HOURLY RAINFALL RATES COULD
APPROACH 2.5" AN HOUR.  THIS COULD LEAD TO SEVERAL OCCURRENCES OF
FLASH FLOODING.

DISCUSSION...A PAIR OF UPPER-LEVEL VORTICES MOVING WESTWARD
OFFSHORE BAJA CALIFORNIA AND THE ISLANDS OFFSHORE SOUTHERN CA ARE
BRINGING A SIGNIFICANT SLUG OF MOISTURE AND INSTABILITY OFF OF
NORTHWEST MEXICO AND THE GULF OF CA/SEA OF CORTEZ INTO THE REGION,
WITH A DEVELOPING CONVECTIVE COMPLEX WITH COOLING TOPS MOVING INTO
SOUTH-CENTRAL AZ AT THE PRESENT TIME.  

RECENT RAP RUNS INDICATE PRECIPITABLE WATER VALUES SHOULD RISE
ABOVE 2" ACROSS THE LOWER CO VALLEY AND INCREASE TOWARDS 1.5" AS
FAR NORTH OF LAS VEGAS, WITH 850 HPA INFLOW INCREASING TOWARDS 30
KTS.  CAPE VALUES INCREASE ABOVE 2000 J/KG PER THE 12Z ARW OVER
THE NEXT SEVERAL HOURS.  THIS BEFITS THE WET MULTI-CELL
ENVIRONMENT.  BOTH SETS OF CORFIDI VECTORS INDICATE THAT ORGANIZED
CONVECTION WOULD MOVE WESTWARD AT 10-15 KTS, WITH A GREATER CHANCE
OF FORWARD PROPAGATION WITHIN THE NORTHERN PORTION OF THE AREA
WHERE DEWPOINTS ARE IN THE 30S AND 40S CURRENTLY -- POSSIBLE
WORDING WAS CHOSEN OVER LIKELY DUE TO THE CELL MOTION EXPECTED. 
MOST OF THE MESOSCALE GUIDANCE QPF OUTPUT IS HANDLING THE ONGOING
ACTIVITY POORLY, WITH THE 00Z PARALLEL NAM/18Z GFS SEEMING TO HAVE
THE BEST HANDLE ON THE THUNDERSTORM ACTIVITY.  CONSIDERING THE
MOISTURE AVAILABLE, RAINFALL RATES UP TO 2.5" AN HOUR, AND LOCAL
AMOUNTS OF 2-4" ARE POSSIBLE WHERE CELLS TRAIN AND/OR BACKBUILD. 
THIS COULD LEAD TO SEVERAL OCCURRENCES OF FLASH FLOODING.

ROTH

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

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

LAT...LON   34341127 32530995 31581099 31651267 32011422 32451493
            34511487 36121572 36851497 36821396 36101264 34341127