000
FXUS66 KPQR 032213
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
230 PM PST WED DEC 3 2008
.SYNOPSIS...HIGH PRESSURE IN BRITISH COLUMBIA IS MOVING INTO THE
NORTHERN ROCKIES WITH INCREASING OFFSHORE LOW LEVEL FLOW OVER THE
FORECAST AREA. OFFSHORE FLOW REMAINS FAIRLY STRONG THROUGH THURSDAY
EVENING THEN SLOWLY DECREASES. UPPER HIGH PRESSURE BUILDS INTO
WESTERN OREGON FRIDAY. DRY WEATHER WILL CONTINUE UNTIL SATURDAY WHEN
SOME PRECIPITATION MAY EDGE INTO THE SOUTH WASHINGTON AND NORTH
OREGON COASTS. VALLEY INVERSIONS WILL BECOME INCREASINGLY STRONG AS
SURFACE WINDS LIGHTEN. THE NEXT FRONTAL SYSTEM WILL MOVE INTO THE
AREA SUNDAY.
&&
.SHORT TERM...LOW LEVEL FLOW HAS TURNED TO LIGHT OFFSHORE AND WILL
BECOME MORE NORTHERLY AS AN UPPER LEVEL LOW PRESSURE AREA APPROACHES
NORTHERN CA. CLOUDS WILL BEGIN TO BREAK UP IN THE NORTH PART LATER
THIS AFTERNOON/EVENING AS THE NORTHERLY FLOW INCREASES. STRATUS
CLOUDS IN THE SOUTHERN AREAS WILL BE HARDER TO CLEAR.
OFFSHORE FLOW STRENGTHENS TONIGHT AS HIGH PRESSURE MOVES INTO THE
NORTHERN ROCKIES. MOST AREAS WILL BE CLEAR WITH OFFSHORE FLOW HOWEVER
EXPECT THE DRIER AIR WILL BE SLOW TO REACH THE SOUTHERN VALLEYS
TONIGHT...WILL LEAVE CLOUDS WITH AREAS OF FOG.
FAIRLY GOOD OFFSHORE FLOW THU WILL KEEP MOST AREAS CLEAR. SOUTHERN
VALLEYS SLOW TO CLEAR BUT FOG/STRATUS SHOULD BREAK UP BY AFTERNOON.
OFFSHORE FLOW STARTS DECREASING LATER THU NIGHT. THIS WILL ALLOW FOG
TO EXPAND IN THE SOUTHERN VALLEYS. NORTH VALLEYS STILL MAINLY CLEAR
AS AMS STILL DRY HOWEVER BY LATE THU NIGHT SOME LOW CLOUD AND FOG
AREAS DEVELOP.
AN UPPER LEVEL HIGH NOSES INTO WESTERN ORE FRI. OFFSHORE FLOW WILL BE
WEAKER FRI WITH THE MAIN E FLOW NEAR THE GORGE. THIS WILL ALLOW
FOG/STRATUS TO REMAIN IN SOUTHERN VALLEYS WITH AFTERNOON CLEARING
ELSEWHERE. LIGHT WINDS...STABLE CONDITIONS AND LIMITED MIXING WILL
CONTINUE INTO SATURDAY
LIKENS
.LONG TERM...A CHANGE IN THE WEATHER PATTERN IS EXPECTED FOR THE
EXTENDED FORECAST. AN UPPER LEVEL SHORTWAVE WILL MOVE OVER THE AREA
SUN...FLATTENING THE UPPER LEVEL RIDGE. THIS FEATURE DESTABILIZES THE
ATMOSPHERE BRINGING COOL SHOWERY WEATHER AS WELL AS TRIGGERING A
STRONG PUSH OF MARINE AIR. THE WEATHER PATTERN BEGINS TO TURN MORE
ACTIVE NEXT WEEK AS THE JET STREAM STARTS MIGRATING SOUTHWARD. A
PACIFIC FRONTAL SYSTEM IS EXPECTED MON NIGHT/TUE...HOWEVER THE EXACT
TIMING IS STILL UNCERTAIN.
&&
.AVIATION...THE STRATUS DECK IS ACTUALLY EXPANDING AS IT IS
EXPERIENCING A BIT OF LIFT AHEAD OF THE UPPER LEVEL FEATURE DROPPING
DOWN FROM THE NORTH. THIS HAS DELAYED THE BREAK UP OF THE LOW CLOUD
LAYER BUT ONCE THE WEAK SHORTWAVE MOVES THROUGH NORTHEAST WINDS AND
DRIER AIR WILL FILTER IN. THIS OFFSHORE FLOW WILL BREAK UP THE
STRATUS FROM NORTH TO SOUTH THIS EVENING AND KEEP ANY FOG THAT FORMS
SHORT LIVED. LOW STRATUS WILL PERSIST LONGEST IN THE SOUTH END OF
THE WILLAMETTE VALLEY EVEN THAT ARE SHOULD CLEAR OUT THU MORNING AS
N TO NE WINDS PUSH DOWN THE VALLEY.
.KPDX AND APPROACHES...MVFR CEILINGS AND VISIBILITIES WILL IMPROVE
LATER THIS AFTERNOON OR EARLY EVENING AS THE STRATUS DECK SCATTERS
OUT. PATCHY GROUND FOG MAY FORM FOR A COUPLE HOURS AROUND MIDNIGHT
BUT WILL DISSIPATE AS EAST WIND BEGIN DURING THE EARLY MORNING
HOURS. RUTHFORD
&&
.MARINE...THE WESTERLY SWELL IN THE COASTAL WATERS IS CURRENTLY
AROUND 7 FT. LONG WAVE LENGTH SWELL FROM A GULF OF ALASKA STORM WILL
ARRIVE TONIGHT INCREASING THE PERIOD FROM 11 SECONDS TO 18 SECONDS.
WHILE WAVE HEIGHTS WILL ONLY INCREASE TO AROUND 9 FT BY THU...THE
LONGER WAVE LENGTH OF THIS NEW SWELL WILL ALLOW IT TO CARRY
SIGNIFICANTLY MORE ENERGY INTO THE SURFACE ZONE AND COLUMBIA RIVER
BAR THAN A SHORTER MORE TYPICAL 9 FT SWELL WOULD HAVE. NORTH TO
NORTHEAST WINDS WILL INCREASE INTO THE 15 TO 20 KT RANGE TONIGHT AND
TOMORROW AS A THERMAL TROUGH BUILDS NORTH ALONG THE COAST. LOOK FOR
THE STRONGEST GUSTS THU AFTERNOON NEAR GAPS AND PASSES IN THE
COASTAL TERRAIN. RUTHFORD
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR/WA...SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA BAR THIS EVENING AND
THU MORNING.
&&
$$
MORE WEATHER INFORMATION ONLINE AT...
Http://weather.gov/portland
THIS DISCUSSION IS FOR NORTHWEST OREGON AND SOUTHWEST WASHINGTON FROM
THE CASCADE CREST TO 60 NAUTICAL MILES OFFSHORE. THE AREA IS COMMONLY
REFERRED TO AS THE FORECAST AREA.
