MESOSCALE PRECIPITATION DISCUSSION 0180
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
247 PM EDT SAT JUL 27 2013
 
AREAS AFFECTED...SOUTHERN NV...NORTHWEST AZ...SOUTHWEST
UT...SOUTHERN CA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 271846Z - 272346Z
 
SUMMARY...ENHANCED LOW LEVEL INFLOW AND THE PRESENCE OF A MID
LEVEL TROUGH WILL PROMOTE ORGANIZATION OF AFTERNOON THUNDERSTORMS
WITHIN A PLUME OF ANOMALOUSLY RICH MONSOON MOISTURE. FLASH
FLOODING IS POSSIBLE.

DISCUSSION...THERE ARE SOME COMPETING FACTORS IN THIS REGION...BUT
MORE PROS THAN CONS FOR HEAVY RAIN. A MID LEVEL TROUGH WAS
SWEEPING UP AIR CHARACTERIZED BY PW VALUES 1.25-1.75
INCHES...RUNNING UP TO 3 STANDARD DEVIATIONS FROM CLIMATOLOGY. THE
TROUGH WAS ANCHORED BY A PRIMARY VORT MAX NEAR SLC. THIS WILL
YIELD A CORRIDOR OF ENHANCED 850-700 MB SOUTHWESTERLY
WINDS...PARTICULARLY OVER SW UT AND NW AZ. ALTHOUGH SOME OF THIS
AREA WAS OVERTURNED BY WIDESPREAD CONVECTION LAST NIGHT...MODELS
AND SPC MESOANALYSIS INDICATE NO SIGNIFICANT DISRUPTION OF THE
GENERALLY FAVORABLE LOWER TO MID LEVEL LAPSE RATES. BY
1830Z...SCATTERED TSRA WERE ALREADY INITIATING IN NW AZ AND
SOUTHERN NV...AND THE ENVIRONMENT SHOULD BECOME MORE SUPPORTIVE
OVER SOUTHWEST UT WITH TIME.

INDIVIDUAL CELLS WILL MOVE NE AT ONLY 5-15 KT. SOME PROPAGATION
BACK TO THE SOUTHWEST AND RESULTANT TRAINING IS LIKELY IN THE
VICINITY OF STORM MERGERS AND IN THE MOUNTAINOUS TERRAIN. LOW
LEVEL FLOW IS LESS FAVORABLE OVER CA/NV...BUT MID LEVELS BECOME
MORE FAVORABLE AS A SECONDARY VORT MAX MERGES BACK INTO THE MID
LEVEL WESTERLIES AND TURNS INTO THE AXIS OF GREATER MOISTURE/CAPE
NEAR AND EAST OF THE CA DESERT. THERE APPEAR TO BE ENOUGH
FAVORABLE FACTORS FOR HEAVY RAIN...INCLUDING HIRES MODEL
AGREEMENT...TO SUSPECT THAT FLASH FLOODING IS LIKELY. EXPECTING A
LITTLE GREATER ORGANIZATION THAN SEEN ON AN AVERAGE SUMMER DAY.

BURKE

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

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

LAT...LON   35681151 34701140 34131197 34111440 34441558 35191637
            36421683 38161540 39521356 39361207 37851175 35681151