MESOSCALE PRECIPITATION DISCUSSION 0167
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1001 AM EDT SUN JUL 21 2013
 
AREAS AFFECTED......SOUTHWEST ARIZONA/SOUTHERN CALIFORNIA... 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 211400Z - 211800Z
 
SUMMARY...RAINFALL RATES OF 1 TO 2 INCHES PER HOUR RESULTING FROM
CONTINUOUS DEEP CONVECTION WILL RESULT IN EXCESSIVE RAINFALL
ACROSS PORTIONS OF SOUTHWEST ARIZONA AND SOUTHERN CALIFORNIA
THROUGH THE MORNING.

DISCUSSION...DEEP CONVECTION CONTINUES TO EXPAND ACROSS THE
HIGHLIGHTED AREA IN RESPONSE TO THE STRONGLY CURVING UPPER JET
BETWEEN AN UPPER LOW NEAR BAJA CALIFORNIA AND AN UPPER HIGH NEAR
THE FOUR CORNERS REGION.  REGIONAL 12Z RAOBS AND GOES SOUNDER
IMAGERY INDICATE PRECIPITABLE WATER VALUES OF 1.75 TO NEAR OR
SLIGHTLY HIGHER THAN 2 INCHES.  INFRARED SATELLITE IMAGERY LOOPS
HAVE RECENTLY SHOWN RAPID CLOUD TOP COOLING WITH THE COLDEST TOPS
IN EXCESS OF 70 CELSIUS WITH BOTH MANUAL AND AUTOMATED TECHNIQUES
SUGGESTING LOCALIZED RAINFALL RATES POSSIBLY IN EXCESS OF 2 INCHES
PER HOUR.  GIVEN NEARLY UNIDIRECTIONAL WIND PROFILES AND THE MOIST
AND UNSTABLE ENVIRONMENT...QUASI-STATIONARY OR BACK-BUILDING CELL
DEVELOPMENT WILL REMAIN LIKELY AS THE DIFFLUENT UPPER JET
CONTINUES TO GENERATE LARGE-SCALE ASCENT OVER THE REGION.  BASED
ON THE LATEST OBSERVATIONAL TRENDS...SOME LOCATIONS MAY RECEIVE
RAINFALL AMOUNTS IN EXCESS OF 3 TO 4 INCHES...POSSIBLY MORE IN
JUST A FEW HOURS OR LESS....WHICH WOULD GREATLY EXCEED FLASH FLOOD
GUIDANCE VALUES.

JAMES

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

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

LAT...LON   33691540 34411424 34161295 33461187 32421184 31821297
            32111459 32771535 33691540