MESOSCALE PRECIPITATION DISCUSSION 0744
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
230 PM EDT WED OCT 19 2016
 
AREAS AFFECTED...WESTERN WA 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 191830Z - 200600Z
 
SUMMARY...HEAVY RAINS WILL ARRIVE ACROSS WESTERN WA LATER THIS
EVENING AND CONTINUE OVERNIGHT.

DISCUSSION...GOES-W SATELLITE IMAGERY SHOWS A LARGE VORTEX OVER
THE GULF OF ALASKA WITH TRAILING JET ENERGY AND AN ASSOCIATED
BAROCLINIC ZONE STRETCHING ALONG A SW/NE ORIENTED AXIS FROM JUST
EAST OF THE DATELINE TO SW CANADA AND THE PACIFIC NORTHWEST.
MICROWAVE DATA INDICATES PW VALUES WITHIN THE MOISTURE PLUME
RANGING FROM NEAR 1 INCH JUST OFF THE WA/OR COAST...TO 1.25 INCHES
SW OF 130W...TO 1.5 INCHES OR POSSIBLY A BIT HIGHER SW OF 140W. 

THE LEADING PORTION OF THE INITIAL RAIN AREA HAS NOW PUSHED INSIDE
OF 130W AND SHOULD REACH THE WA COAST WITHIN A FEW HOURS. AREA
RADARS FROM WESTERN WA INCLUDING KLGX CONFIRM THE LEADING EDGE OF
WARM ADVECTION RAINFALL OFFSHORE. CURRENT AMSU MICROWAVE DATA
INDICATES AREAL AVERAGE RAINFALL RATES FROM A FEW HUNDREDTHS TO
OVER .10"/HR AND A FEW PIXELS TO NEAR .25"/HR OFFSHORE. THE
RAINFALL INTENSITY SHOULD INCREASE LATER THIS EVENING AND
OVERNIGHT AS SHORTWAVE ENERGY CURRENTLY LOCATED JUST W OF 140W
APPROACHES ALONG WITH AN EXPECTED INCREASE IN THE SOUTHWESTERLY
850-700MB FLOW TO THE 40-55 KT RANGE DIRECTED INTO THE TERRAIN OF
WESTERN WA. THIS SHOULD PROVIDE A PERIOD OF MODERATE TO HEAVY
RAINFALL PRIMARILY FOR WESTERN WASHINGTON...WITH RATES LIKELY
APPROACHING .50"/HR AND LEADING TO AT LEAST SOME CONCERN GIVEN THE
RECENT RAINFALL OVER THIS AREA FROM THE MOST RECENT ATMOSPHERIC
RIVER EVENT.

THE LATEST NMMB AND ESPECIALLY THE ARW/NSSL-WRF GUIDANCE SHOW
HEAVY OROGRAPHICALLY ENHANCED RAINS ARRIVING BY 06Z AND CONTINUING
THEREAFTER WITH EVEN HEAVIER RATES. EXPECT BETWEEN 1 TO 2 INCHES
OF NEW RAINFALL ACROSS ESPECIALLY THE OLYMPIC PENINSULA AREA
THROUGH 06Z. WILL CONTINUE TO MONITOR.

ORRISON 

ATTN...WFO...PQR...SEW...

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

LAT...LON   48542461 48312401 48292299 47402270 46412285 
            46182357 46342390 47112434 48132473