MESOSCALE PRECIPITATION DISCUSSION 0792
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
425 AM EST SAT DEC 10 2016
 
AREAS AFFECTED...FAR SW ORE INTO NW CA 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 100924Z - 101800Z
 
SUMMARY...A ROBUST ATMOSPHERIC RIVER WILL CONTINUE TO SUPPORT
MODERATE TO LOCALLY HEAVY RAINFALL RATES THROUGH THE MORNING ALONG
THE NRN COAST OF CA INTO THE NRN SIERRA NEVADA/SRN CASCADE
MOUNTAINS. ADDITIONAL RAINS OF UP TO 3 TO 4 INCHES ARE POSSIBLE
THROUGH 18Z. 

DISCUSSION...EARLY MORNING WATER VAPOR IMAGERY SHOWED CONFLUENT
MID-UPPER LEVEL FLOW OVER THE EASTERN NORTH PACIFIC WITH THE AXIS
OF DILATATION LOCATED NEAR LATITUDE 40N. AT 09Z...A VORTICITY MAX
WAS LOCATED NEAR 46N 153W IN NWLY FLOW. A SECOND BUT MORE SHEARED 
VORTICITY MAX WAS LOCATED NEAR 36N 152W IN SWLY FLOW.
DOWNSTREAM...GOES HD WINDS CONFIRMED THE PRESENCE OF A 110-130 KT
UPPER LEVEL JET WAS CONTINUING TO MAKE ITS WAY EASTWARD IN
PROXIMITY TO THE MID LEVEL CONFLUENCE. CIRA LAYERED PW PRODUCT
SHOWED A PLUME OF MODIFIED TROPICAL MOISTURE STREAMING NORTH
ACROSS HAWAII AND THEN NEWD TOWARD THE CALIFORNIA COAST...WITH A
DIRECT CONNECTION STILL SHOWN TO THE ITCZ IN THE LOWER...MIDDLE
AND UPPER LEVELS OF THE TROPOSPHERE. BLENDED TPW IMAGERY AND
RECENT RUNS OF THE RAP SHOWED THE NOSE OF A SIZABLE PRECIPITABLE
WATER PLUME AT OR ABOVE 1.50 INCHES...REACHING NEAR 38N 125W IN
SWLY LOW LEVEL FLOW.

SHORT TERM RAP FORECASTS TAKE THE TWO VORTICITY MAXIMA DOWNSTREAM
AND TIGHTEN THE CONFLUENT FLOW ALONG WITH A STRENGTHENING OF THE
250 MB JET TO 130-150 KTS. THE LEFT EXIT REGION OF THIS JET STREAK
IS FORECAST TO REACH THE CA/OR BORDER ALONG THE COAST BY 12Z ALONG
WITH PRECIPITABLE WATER VALUES OF NEARING 0.9 TO 1.2 INCHES
NEARING THE NORTHERN CA COAST.  GLOBAL MODELS INDICATE THAT THE
LOWER LEVELS ARE EXPECTED TO SEE 850-700 MB WINDS OF ROUGHLY 30-40
KT FROM THE WSW...PERPENDICULAR TO THE COASTAL RANGES OF DEL NORTE
AND HUMBOLDT COUNTIES WHERE RAINFALL RATES SHOULD APPROACH 0.5
IN/HR BUT THE STEADY DURATION OF FLOW ORTHOGONAL TO THE TERRAIN
COULD ALLOW AN ADDITIONAL 3-4 INCHES OF RAIN BY 18Z. 

FARTHER SOUTH...MOISTURE IS EXPECTED TO REACH AS HIGH AS 1.4 TO
1.5 INCHES ALONG THE COAST OF MENDOCINO AND SONORA COUNTIES WITH
850-700 MB FLOW AS HIGH AS 50 KTS DURING THE MORNING. THE
ANOMALOUS MOISTURE WILL EXTEND DOWNSTREAM INTO THE NRN SIERRA
NEVADA...WHERE THE SNOW LEVEL IS EXPECTED TO RISE ABOVE 10000 FT
BY EARLY MORNING.  IT IS HERE WHERE THE HIGHEST RAINFALL RATES ARE
EXPECTED...PERHAPS OWING TO SOME WEAK INSTABILITY. RAINFALL RATES
BETWEEN 0.50 AND 1.0 IN/HR ARE EXPECTED THROUGH AT LEAST 15Z ALONG
THE COASTAL RANGES AND INTO THE UPSLOPE REGIONS OF THE SIERRA
NEVADA. 

THE AXIS OF DEEP MOISTURE SHOULD GRADUALLY BE SHUNTED SOUTHWARD BY
A SYSTEM LOCATED IN THE NORTHERN STREAM FLOW.  THIS SHOULD RESULT
IN RAINFALL RATES STARTING TO DECREASE BY 18Z.

BANN

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

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

LAT...LON   42322425 41822220 41122083 39461994 37871943 
            37822004 38812134 40062206 39962273 39362276 
            38372295 39002415 41382493