MESOSCALE PRECIPITATION DISCUSSION 0266
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
221 PM EDT TUE AUG 12 2014
 
AREAS AFFECTED......ARIZONA/S. CALIFORNIA... 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 121820Z - 122320Z
 
SUMMARY...FLASH FLOODING MAY ACCOMPANY INCREASING THUNDERSTORM
DEVELOPMENT THROUGH THE AFTERNOON AS TROUGH EXITS SOUTHWEST
ARIZONA.

DISCUSSION...THE SHORTWAVE TROUGH OVER SOUTHWEST ARIZONA IS
COMPRISED OF 3 DISTINCT MESOSCALE CIRCULATIONS LINED UP IN A ROW
BETWEEN YUMA AND TUCSON DRIFTING NORTHWESTWARD. ALTHOUGH CLOUD
COVER REMAINS EXTENSIVE...THE ANOMALOUSLY MOIST ENVIRONMENT WITH
PW VALUES NEAR OR IN EXCESS OF 2 INCHES IS HELPING TO YIELD
AVERAGE CAPE VALUE OF 1000-3000 J/KG. RADAR AND SATELLITE IMAGERY
CONTINUE TO SHOW SLOW BUT STEADY CONVECTIVE ELEMENTS FORMING
AROUND THE PERIMETER OF THE MESOSCALE CIRCULATIONS AND WITHIN
VICINITY OF THE TERRAIN GRADIENTS...INCLUDING THE SAN GABRIELS/SAN
BERNARDINOS/MOGOLLON RIM.  

GIVEN NEARLY SATURATED THERMODYNAMIC PROFILES AND ONLY SLOWLY
VEERING WINDS WITH HEIGHTS...CELL MOTIONS ARE EXPECTED TO AVERAGE
TOWARD THE NORTHWEST AT 10 TO 20 KNOTS.  THESE CONDITIONS FAVOR
RAIN RATES ANYWHERE FROM 0.5 TO 1.25 INCHES PER HOUR...WHICH IN
SOME CASES WOULD EXCEED HOURLY FFG VALUES OF 0.75 TO 1 INCH...AND
COLD LEAD TO FLASH FLOODING.

JAMES

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

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

LAT...LON   32651634 34221679 35461532 35661320 34641112 32560988
            31311094 31731430 32651634