MESOSCALE PRECIPITATION DISCUSSION 0013
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
111 AM EST THU JAN 21 2016
 
AREAS AFFECTED...NORTHWEST OR & WESTERN WA 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 210610Z - 211800Z
 
SUMMARY...HOURLY RAIN RATES ARE EXPECTED TO INCREASE IN THE WAKE
OF A WARM FRONTAL PASSAGE ACROSS THE REGION.  HOURLY RAIN RATES
EXCEEDING 0.50" ARE POSSIBLE, MAINLY BEYOND 09Z.

DISCUSSION...A MID- TO UPPER-LEVEL LOW IS DRIFTING NORTHEAST NEAR
47N/140W.  TO ITS SOUTHEAST, A WARM FRONT IS MOVING UP THE COASTS
OF NORTHWEST OR INTO SOUTHWEST WA, WITH A COLD FRONT WELL
OFFSHORE.  WITHIN THE ATMOSPHERIC RIVER, IN THIS CASE A PINEAPPLE
CONNECTION, PRECIPITABLE WATER VALUES (PWS) RUN 1.25-1.5" PER THE
LATEST AMSU PASS.  PWS ALONG THE COAST OF COASTS OF WA/OR RANGE
BETWEEN 0.85-1.1" PER RECENT GPS VALUES.  THE LATEST AMSU RAINFALL
RATE PASS INDICATES JUST A SMALL BULLSEYE OF RAINFALL RATES BTWN
0.25"-0.33"/HR OFFSHORE THE OR COAST.

THE NORTHEAST-MOVING UPPER LOW SHOULD KEEP THE ATMOSPHERIC RIVER
ESSENTIALLY IN PLACE DURING THE MORNING HOURS, WHICH WILL ALLOW
FOR CONTINUOUS RAINFALL ACROSS THE PACIFIC NORTHWEST, PARTICULARLY
NEAR THE COAST AND INTO THE CASCADES.  SOUTHWEST LOW-LEVEL INFLOW
SHOULD WAVER IN AND NEAR THE 50-60 KT RANGE FOR MUCH OF THE
PERIOD, ENHANCED OCCASIONALLY AS VERY WEAK SHORTWAVES MOVE THROUGH
THE AREA.  

RAINFALL RATES ARE EXPECTED TO RISE ABOVE 0.50" AN HOUR,
PARTICULARLY PAST ~09Z IN THE OLYMPIC PENINSULA AND ~14Z ACROSS
THE NORTHERN OR COASTAL RANGE AND PORTIONS OF THE WA/OR CASCADES.
THE CAM GUIDANCE SUGGESTS THAT DURING THE NEXT TWELVE HOURS, LOCAL
AMOUNTS EXCEEDING 3" ARE POSSIBLE.  ENHANCEMENT FROM RIGHT
ENTRANCE REGION JET DYNAMICS LATE IN THE PERIOD MAY ALSO HELP RAIN
RATES LATER IN THE DAY.  THIS INFORMATION WAS COORDINATED WITH
SAB/NESDIS. 

ROTH

ATTN...WFO...OTX...PDT...PQR...SEW...

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

LAT...LON   49042183 48982113 47472103 47311992 46772029 
            46002090 45292158 45312186 45822233 46022287 
            45742316 45542319 44752360 44902414 46442436 
            47962479 48392457 48032297 47262319 46762295 
            47072252 47892193