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
Last Updated: 230 PM EDT WED OCT 19 2016