MESOSCALE PRECIPITATION DISCUSSION 0584
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
444 AM EDT SUN OCT 18 2015
 
AREAS AFFECTED...CENTRAL/SOUTHEAST CA...NV 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 180830Z - 181400Z
 
SUMMARY...INCREASING COVERAGE OF SHOWERS AND THUNDERSTORMS ARE
ANTICIPATED OVER THE NEXT FEW HOURS...WITH LOCALLY INTENSE
RAINFALL RATES. LOCALIZED FLASH FLOODING IS POSSIBLE.

DISCUSSION...WV AND GOES-RGB AIRMASS IMAGERY ARE INDICATING A
WELL-DEFINED SHORTWAVE TROUGH EJECTING EAST INTO CENTRAL CA VERY
EARLY THIS MORNING...AND THIS IS INTERACTING WITH AN ANOMALOUSLY
MOIST AIRMASS THROUGHOUT THE SOUTHWEST U.S...WHERE PWATS ARE ON
THE ORDER OF 4 SIGMAS ABOVE THE MEAN. GOES-SOUNDER PWATS ARE ON
THE ORDER OF 1 TO 1.25 INCHES OVER THE INTERIOR AREAS OF SOUTHERN
CA...AND UP TO AS HIGH AS 1 INCH OVER CENTRAL AND SOUTHERN NV. 

OVER THE LAST COUPLE OF HOURS THERE HAS BEEN AN EXPANSION OF
COOLING CONVECTIVE TOPS OVER PORTIONS OF SOUTHEAST CA AND NEAR THE
SOUTHERN SIERRA-NEVADA...AS WELL AS PORTIONS OF CENTRAL AND
SOUTHERN NV. THE CONVECTION IS BEING PRIMARILY AIDED BY AN
INCREASINGLY DIVERGENT UPPER LEVEL FLOW PATTERN AHEAD OF THE
APPROACHING SHORTWAVE WITH STRONGER DEEP LAYER ASCENT TAKING
ADVANTAGE OF A MODESTLY UNSTABLE AIRMASS PER GOES-SOUNDER LI
DATA...AND THE ANOMALOUS MOISTURE PROFILES.

HIRES GUIDANCE FROM 00Z INCLUDING THE ARW AND NMMB...COUPLED WITH
RECENT HRRR RUNS SUGGEST THAT CONVECTION SHOULD TEND TO BECOME A
BIT MORE EXPANSIVE IN COVERAGE OVER THE NEXT FEW HOURS...AND THE
LATEST EXPERIMENTAL GLD-360 LIGHTNING DENSITY PRODUCT IS SHOWING A
GRADUAL INCREASE IN STRIKE INTENSITY WHICH SUGGESTS MORE VIGOROUS
ASCENT/UPDRAFT TRENDS.

RAINFALL RATES OF UP TO 1 TO 1.5 INCHES/HR ARE POSSIBLE...WITH
LOCALIZED TOTALS OF 2 TO 3 INCHES NOT OUT OF THE QUESTION. THESE
RAINS WILL RESULT IN LOCALLY SIGNIFICANT RUNOFF PROBLEMS IN THE
VICINITY OF HIGHER TERRAIN...AND WILL ALSO FOCUS CONCERNS FOR
FLASH FLOODING IN AND AROUND DRY WASHES/ARROYOS. WILL CONTINUE TO
MONITOR.

ORRISON

ATTN...WFO...HNX...LKN...LOX...REV...SGX...VEF...

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

LAT...LON   41541744 41451577 39871516 38931506 37331534 
            35861600 35171666 34531758 34641871 35231907 
            36321916 37371965 38451950 39171881