MESOSCALE PRECIPITATION DISCUSSION 0298
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
953 AM EDT TUE AUG 19 2014
 
AREAS AFFECTED...AZ...SOUTHEASTERN CA/SOUTHERN NV/SOUTHWESTERN
UT... 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 191353Z - 191823Z
 
SUMMARY...EARLY MORNING CONVECTION CONTINUES TO THRIVE ACROSS
CENTRAL AZ AND UP TOWARD THE NV/UT BORDER. THE ATMOSPHERE REMAINS
MOIST AND UNSTABLE WITH FLASH FLOODING POSSIBLE...PARTICULARLY IN
REGIONS OF MORE SLOPED TERRAIN.

DISCUSSION...A RATHER IMPRESSIVE 12Z SOUNDING WAS OBSERVED IN THE
PHOENIX AZ AREA WITH PWATS NEARING 2 INCHES  AND AMPLE
SURFACE-BASED CAPE OF OVER 2000 J/KG. THE 11Z RAP SHOWED A RATHER
WELL DEFINED TONGUE OF INSTABILITY EXTENDING UP FROM THE GULF OF
CA/SEA OF CORTEZ NORTHWARD INTO THE DESERT SOUTHWEST. THIS HAS
COMBINED WITH AN IMPRESSIVE SURGE OF MOISTURE WITH PWATS IN THE
1.75 TO 2 INCH RANGE ANCHORING SOUTHERN AZ/SOUTHEASTERN CA. THIS
COMBINATION WILL CONTINUE TO BE IN PLACE AND BE FURTHER FUELED BY
DIURNAL HEATING TO BRING MULTIPLE ROUNDS OF HEAVY RAINFALL. GIVEN
THE COMPLEX TERRAIN OVER THE REGION...FLASH FLOODING WILL BE
POSSIBLE...PARTICULARLY WITH STORM UPDRAFTS THAT HAVE LONGER
RESIDENCE TIMES. AREAS OF NORTHWESTERN AZ HAVE ALREADY EXPERIENCED
FLASH FLOOD CONDITIONS OVERNIGHT WHICH MAKES THE REGION MORE
SUSCEPTIBLE TO ADDITIONAL ISSUES THE NEXT SEVERAL HOURS.
OVERALL...THE HIGH-RESOLUTION MODELS HAVE A CONSISTENT SIGNAL IN
DROPPING HEAVY RAINFALL IN AN AXIS EXTENDING FROM SOUTHEASTERN AZ
NORTHWESTWARD TOWARD THE NV/UT/AZ BORDER. WILL CONTINUE TO MONITOR
THE SITUATION FOR A POSSIBLE REISSUANCE THIS AFTERNOON.


RUBIN-OSTER

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

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

LAT...LON   379511422 376411334 369411293 358411230 347911098 
            341211041 334211022 326611093 322711241 325711316 
            338611392 348411496 358911523 374611531