MESOSCALE PRECIPITATION DISCUSSION 0582
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1241 PM EDT SAT OCT 17 2015
 
AREAS AFFECTED......CENTRAL VALLEY INTO WESTERN SLOPES OF THE
SIERRAS... 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 171640Z - 172040Z
 
SUMMARY...NUMEROUS...MULTIPLE ROUNDS OF SHOWERS AND THUNDERSTORMS
WILL CONTINUE ACROSS THE CENTRAL VALLEY INTO THE WESTERN SLOPES OF
THE SIERRAS THIS AFTERNOON WITHIN THE CONTINUED ANOMALOUS MOIST
ENVIRONMENT. LOCALIZED RAINFALL RATES AROUND 0.75 INCH PER HOUR
COULD PRODUCE FLASH FLOODING...PARTICULARLY IN BURN SCAR AREAS. 

DISCUSSION...PER THE LATEST SATELLITE WATER VAPOR AND LONGWAVE IR
IMAGERY...AN AREA OF ORGANIZED CONVECTION CONTINUES TO EXPAND N-S
ACROSS THE CENTRAL VALLEY LATE THIS MORNING. THE ACTIVITY IS BEING
SUPPORTED BY INCREASING UPPER LEVEL DIFFLUENCE AND DEEP-LAYER
ASCENT TO THE EAST OF THE AMPLIFIED...NEGATIVELY-TILTED MID LEVEL
SHORTWAVE. THE STEEPENING LAPSE RATES ALOFT IS ALLOWING FOR
MUCAPES UP TO 500 J/KG OVER THE CONVECTIVE GENESIS REGION
CURRENTLY...WHICH PER THE LATEST RAP/HRRR/ARW FORECASTS IS
EXPECTED TO CONTINUE THROUGH THE AFTERNOON HOURS. MEANWHILE...THE
DEEP MOISTURE PROFILE IS OPTIMAL FOR THE TIME OF YEAR IN TERMS OF
PRECIPITATION EFFICIENCY...WITH WET BULB ZERO LEVELS BETWEEN 8-8.5
KFT AGL AND PWS AROUND 1.25 INCHES WHICH ARE 4-5 STANDARD
DEVIATIONS ABOVE NORMAL (NEAR RECORD).   

AS THE AFTERNOON PROGRESSES... THE CONTINUED ROBUST SYNOPTIC SCALE
FORCING AHEAD OF THE SHORTWAVE TROUGH ALONG WITH THE FAVORABLE
THERMODYNAMIC PROFILES (MOISTURE AND INSTABILITY) WILL ALLOW FOR
ADDITIONAL MULTI-CELLULAR CONVECTION OVER THE AFFECTED AREA...WITH
A CONTINUED RISK FOR EXCESSIVE SHORT TERM RAINFALL RATES AND FLASH
FLOODING (AGAIN ESPECIALLY OVER BURN SCARS). IN TERMS OF THE
HIGHER RESOLUTION GUIDANCE...THE RGEM AND TO SOME EXTENT THE
LATEST RAP/HRRR/EXPERIMENTAL HRRR RUNS SEEM TO BE CAPTURING THE
CURRENT MORE FAVORABLY. 

HURLEY

ATTN...WFO...HNX...REV...STO...

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

LAT...LON   39522015 39201989 38491986 37611930 37091901 
            36871958 37792058 38612096 39492062 
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