MESOSCALE PRECIPITATION DISCUSSION 0685
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1250 PM EST MON DEC 21 2015
 
AREAS AFFECTED...SOUTHWEST OR/NORTHERN CA 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 211750Z - 220300Z
 
SUMMARY...A DEEP MOISTURE SURGE...ASSOCIATED WITH A VERY STRONG
JET STREAK...WILL PRODUCE HEAVY RAINFALL ACROSS FAR SOUTHWEST OR
INTO NORTHERN CA INTO THE EARLY EVENING HOURS..

DISCUSSION...WATER VAPOR IMAGERY SHOWED A STRONG SHORT WAVE COMING
ASHORE OVER WESTERN OR. AHEAD AND SOUTH OF THE SHORT WAVE...A
PLUME OF 1.25 INCH PRECIPITABLE WATER AIR (DEPICTED NICELY IN THE
MOST RECENT BLENDED TOTAL PRECIPITABLE WATER IMAGE) ON A 35 TO 45
KNOT LOW LEVEL WESTERLY FLOW (PER RECENT VWP) HAD REACHED NORTHERN
CA BEHIND A WARM FRONT. KBHX RADAR AND THE MOST RECENT MRMS
PRECIPITATION RANGE IMAGE SHOWED HOURLY RAINFALL RATES AROUND 0.50
INCHES. 

RAINFALL RATES BETWEEN 0.50 AND 0.75 INCHES ARE EXPECTED WITH COLD
FRONTAL PASSAGE...WHICH IS EXPECTED AROUND 21Z ALONG THE NORTHERN
CA COAST (PER THE LATEST RAP/HRRR SOLUTIONS)...AND CLOSER TO 00Z
TO 01Z OVER THE SIERRA NEVADA RANGE. THE 1.25 INCH PRECIPITABLE
WATER PLUME (WHICH IS BETWEEN TWO AND THREE STANDARD DEVIATIONS
ABOVE THE MEAN) IS EXPECTED TO DROP SLOWLY SOUTH THROUGH THE
EVENING HOURS...MAINTAINING A DEEP MOISTURE SOURCE FOR HEAVY
RAINFALL...ESPECIALLY OVER THE WINDWARD SLOPES OF THE CA COASTAL
RANGES AND THE EVENTUALLY THE SIERRA NEVADA RANGE.

ADDITIONAL RAINFALL AMOUNTS BETWEEN 2 AND 4 INCHES ARE POSSIBLE
INTO THE EARLY EVENING HOURS...WITH MOST OF THE HIGH RESOLUTION
MODELS PLACING THE HIGHEST AMOUNTS ON THE WINDWARD SIDE OF THE
COASTAL CA RANGE.


HAYES

ATTN...WFO...EKA...HNX...MFR...MTR...STO...

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

LAT...LON   43022422 42892389 42292337 41612316 40992267 
            40412206 39802121 39312041 38252001 37672018 
            37632051 37982088 39062153 39832217 40032258 
            39702289 39642289 39492293 38892289 38442306 
            38582347 39102380 39722414 41772459 42382467