MESOSCALE PRECIPITATION DISCUSSION 0425
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
312 AM EDT FRI AUG 07 2015
 
AREAS AFFECTED...SOUTHEAST NV...SOUTHERN CA...NORTHWEST
AZ...SOUTHWEST UT 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 070705Z - 071230Z
 
SUMMARY...EXPANDING COVERAGE OF SHOWERS AND THUNDERSTORMS THIS
MORNING SHOULD RESULT IN AT LEAST SOME ADDITIONAL RUNOFF CONCERNS.

DISCUSSION...THE LATEST GOES-RGB AIRMASS IMAGERY SHOWS A
WELL-DEFINED UPPER LOW NOW MOVING INTO CENTRAL CA WHICH IS HELPING
TO PROVIDE LARGER SCALE DIVERGENCE/FORCING DOWNSTREAM OVER
PORTIONS OF SOUTHERN CA/NV/UT AND AZ. ADDITIONALLY...THE
RGB-AIRMASS PRODUCT SUGGESTS A SEPARATE SMALLER SCALE VORT THAT IS
GETTING STRETCHED OVER FAR SOUTHERN CA AND INTO WESTERN AZ. THE
COMBINATION OF THESE FEATURES IS HELPING TO EXPAND THE SHOWER AND
THUNDERSTORM ACTIVITY OVER SOUTHERN CA AND ESPECIALLY ALONG THE
BORDER WITH AZ. ADDITIONAL SHOWER ACTIVITY IS CONTINUING TO FOCUS
FARTHER NORTH OVER PARTS OF SOUTHEAST NV AND ESPECIALLY OVER
SOUTHWEST UT WHERE THE RAINS HAVE BECOME SOMEWHAT CONCENTRATED
OVER THE LAST HOUR.

OVER THE NEXT FEW HOURS...SOME EXPANSION IN THE COVERAGE OF
CONVECTION IS EXPECTED AS STRONGER FORCING AHEAD OF THE UPPER LOW
ARRIVES AND INTERACTS WITH AN INCREASINGLY MOIST AND AT LEAST
MODESTLY UNSTABLE AIRMASS. THE LATEST GLD-LIGHTNING DENSITY
PRODUCT SHOWS AN UPTICK IN STRIKE ACTIVITY OVER THE LAST HOUR
WHICH ALREADY SUGGESTS ARRIVAL OF STRONGER FORCING.
ADDITIONALLY...THE LATEST CIRA LAYERED PW ANALYSIS ALSO SHOWS A
RATHER MARKED INCREASE IN MID TO HIGH LEVEL MOISTURE WHICH SHOULD
ALLOW CONVECTION TO BECOME INCREASINGLY RAINFALL EFFICIENT WITH
HEAVIER RAINFALL RATES.

RAINFALL RATES OF 1 TO 2 INCHES/HR ARE EXPECTED LOCALLY...AND WITH
EXPANDING COVERAGE...FLASH FLOODING WILL BE POSSIBLE. THIS WILL
ESPECIALLY BE THE CASE OVER AREAS OF HIGHER TERRAIN AND WITHIN DRY
WASHES.

ORRISON

ATTN...WFO...FGZ...PSR...SGX...SLC...VEF...

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

LAT...LON   38571333 38001234 36861207 34981254 33761405 
            33501531 33711600 34131639 35001649 36291587 
            37591539 38381445