Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 011629
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
929 AM PDT TUE SEP  1 2015

.SYNOPSIS...A COLD FRONT WILL SLOWLY MOVE SOUTHWARD INTO SOUTHWEST
WASHINGTON AND EXTREME NORTHWEST OREGON TODAY...AND INTO THE
REMAINDER OF NORTHWEST OREGON TONIGHT FOR A LITTLE LIGHT RAIN OR
SHOWERS. THE SOUTHERN PART OF THE ASSOCIATED TRAILING UPPER LOW WILL
SLOWLY EXTEND INTO SOUTHWEST WASHINGTON AND NORTHWEST OREGON
WEDNESDAY FOR MORE SHOWERS...AND LINGER OVER THE PACIFIC NORTHWEST
THURSDAY. ENERGY ON THE WEST SIDE OF THE UPPER LOW WILL DROP DOWN
ALONG THE COAST THURSDAY NIGHT THEN SWING INLAND MAINLY SOUTH OF OUR
FORECAST AREA FRIDAY. HOWEVER...THE COLDER AIR ALOFT WILL BE MORE
OVER OUR AREA FRIDAY FOR A GREATER CHANCE OF AFTERNOON AND EVENING
SHOWERS AND THUNDERSTORMS. THE LOW WILL MOVE OFF TO THE EAST THIS
WEEKEND FOR IMPROVING WEATHER...THOUGH ANOTHER SYSTEM IS POSSIBLE
EARLY NEXT WEEK.

&&

.UPDATE...RADAR THIS MORNING SHOWS LIGHT RAIN OVER MAINLY PACIFIC AND
CLATSOP COUNTIES ASSOCIATED WITH A COLD FRONT MOVING SOUTHEAST ALONG
THE COAST. RAIN WILL BE VERY SLOW TO MOVE INLAND AND WILL TEND TO
DISSIPATE AS IT DOES SO...SO HAVE LOWERED POPS FOR THIS MORNING FOR
MOST AREAS OUTSIDE OF WHERE RAIN IS CURRENTLY FALLING. 850 MB WINDS
TURN MORE WESTERLY LATER TODAY AND TONIGHT...WHICH MAY RAIN SHADOW
THE VALLEY SO HAVE ALSO LOWERED POPS A BIT THERE THROUGH THE LATE
EVENING. LOOKS LIKE THE NORTH COAST...COAST RANGE...AND CASCADES WILL
SEE THE BEST CHANCE FOR RAIN FOR THE NEXT 24 HOURS OR SO. THE UPPER
LOW REMAINS OVER BRITISH COLUMBIA THIS MORNING AND THROUGH THE DAY
TODAY...SO DYNAMICS SHOULD NOT BE PRESENT FOR ANY THUNDER.

THIS MORNING IS STARTING OUT MAINLY CLEAR IN THE CENTRAL FORECAST
AREA WITH STRATUS FROM THE FRONT NORTH AND WHAT IS PROBABLY MARINE
STRATUS SOUTH. THE MARINE STRATUS WILL SLOWLY DISSIPATE THIS MORNING
BUT FRONTAL STRATUS WILL SPREAD ACROSS THE AREA. OVERALL MOST INLAND
LOCATIONS WILL SEE SOME SUN BEFORE OVERCAST SKIES ENVELOP THE AREA.
BOWEN

.SHORT TERM (PREVIOUS DISCUSSION)...SATELLITE IMAGERY AND NATIONAL
WEATHER SERVICE DOPPLER RADAR SHOW A FRONT ALONG THE CENTRAL
WASHINGTON COAST EARLY THIS MORNING. THE UPPER CLOUDS WITH THIS FRONT
HAVE SHEARED OFF TO THE EAST OF THE CASCADES. THE LOWER LEVEL CLOUDS
ARE SLOWLY MOVING SOUTHWARD. THE MODELS SHOW IT SLOWLY MOVING INTO
SOUTHWEST WASHINGTON AND EXTREME NORTHWEST OREGON TODAY...THEN ACROSS
THE REMAINDER OF NORTHWEST OREGON TONIGHT. INFRARED SATELLITE IMAGERY
SHOWS A JET STREAK/SHORT WAVE OUT AROUND 45N/135W THAT THE MODELS
MOVE THROUGH THE PACIFIC NORTHWEST THIS AFTERNOON AND EVENING. THIS
APPEARS TO BE THE FEATURE THAT WILL KEEP THE FRONT SOMEWHAT ACTIVE AS
IT MOVES INTO OUR FORECAST AREA. PRECIPITATION WILL NOT BE A LOT WITH
THIS FRONT...PERHAPS A QUARTER INCH ON THE NORTH COAST AND IN THE
COASTAL MOUNTAINS...UP TO A TENTH IN THE NORTH VALLEY...AND ONE OR
TWO TENTHS IN THE CASCADES...WITH LESSER AMOUNTS IN THE SOUTH.

ON WEDNESDAY THE SOUTHERN PART OF THE ASSOCIATED UPPER LOW EXTENDS
SOUTHWARD INTO OUR FORECAST AREA. THIS SHOULD PRODUCE SOME DECENT
SHOWERS ESPECIALLY DURING THE FIRST HALF OR SO OF THE DAY AS A DECENT
SHORT WAVE MOVES THROUGH. THERE MAY BE ENOUGH COOLING ALOFT FOR A
SLIGHT CHANCE OF THUNDER AS WELL...AND MODEL LIFTED INDICES SUPPORT
THIS IDEA.

THE UPPER TROUGH LINGERS AND SAGS A LITTLE FARTHER SOUTH ON THURSDAY
FOR SOME MORE SHOWERS...AND A ANOTHER SHORT WAVE MOVES THROUGH AS
WELL. THERE MAY BE ANOTHER CHANCE OF THUNDER AS WELL IN THE AFTERNOON
AND EVENING.

TEMPS WILL STAY BELOW NORMAL THROUGH THE PERIOD...HOVERING ON ONE
SIDE OR THE OTHER OF 70 IN THE NORTH...AND A FEW DEGREES WARMER NEAR
EUGENE.

SNOW LEVELS WILL BE LOWERING TO POSSIBLY AS LOW AS 6000 TO 7000 FEET
AROUND MOUNT HOOD NORTHWARD...THE LOWEST WE HAVE SEEN SINCE SPRING.
TOLLESON

.LONG TERM...THURSDAY NIGHT THROUGH MONDAY. THE MODELS ARE COMING
TOGETHER WITH THE UPPER LOW DROPPING SOUTHWARD ON THURSDAY NIGHT AND
FRIDAY. THE INITIAL MAIN ENERGY DROPS SOUTH ALONG THE COAST AND THEN
SWINGS INLAND MAINLY TO OUR SOUTH. BUT THEN WE WILL BE UNDER A
BROADER PORTION OF THE COLD POOL ALOFT FOR FRIDAY AFTERNOON AND
EVENING...AND EXPECT SOME DIURNAL SHOWERS AND POSSIBLY A FEW
THUNDERSTORMS TO DEVELOP AROUND THE AREA. THE UPPER LOW MOVES OFF TO
THE EAST OVER THE WEEKEND THAT SHOULD BRING SOME IMPROVING WEATHER TO
THE AREA. THE MODELS SUGGEST THE NEXT SYSTEM COULD ARRIVE SOMETIME
EARLY NEXT WEEK. TOLLESON

&&

.AVIATION...MOSTLY VFR CONDITIONS THIS MORNING. HOWEVER...THERE
ARE MVFR CIGS AND VSBYS AT KAST AS A FRONT IS PRODUCING MODERATE
RAIN FOR THE WASHINGTON AND NORTHERN OREGON COAST. THE FRONT WILL
STALL IN THIS REGION BEFORE SLOWLY MOVING INLAND LATE THIS
AFTERNOON AND OVER THE CENTRAL OREGON CASCADES THIS EVENING.
EXPECT MVFR CIGS WITH THE HEAVIER RAIN AS THE FRONT MOVES ACROSS
THE REGION. POST COLD FRONTAL ONSHORE WIND MAY RESULT IN IFR
CIGS FOR THE COAST THIS AFTERNOON. INLAND SITES SHOULD NOT DROP
LOWER THAN A HIGH END MVFR AT WORST AND PROBABLY REMAIN VFR WITH
CIGS AROUND 035.

KPDX AND APPROACHES...VFR ALTHOUGH CIGS LOWER TO 035 AS A WEAK
COLD FRONT CROSSES THE FIELD 20-23Z. TJ/JBONK

&&

.MARINE...A WEAK COASTAL JET WILL DEVELOP THIS MORNING WITH GUSTY
WINDS UP TO 25 KT POSSIBLE THROUGH THIS AFTERNOON...MAINLY ALONG
THE NORTH OREGON AND SOUTH WASHINGTON COASTS. THESE WINDS MAY BE
ENOUGH TO INCREASE WIND WAVES...AND OVERALL SEA HEIGHTS ABOVE 10
FT AND HAVE ISSUED A SMALL CRAFT ADVISORY FOR SEAS FOR THE
NORTHERN WATERS WITHIN 10 NM.

A SURFACE LOW OVER THE GULF OF ALASKA...JUST OFFSHORE OF THE DIXON
ENTRANCE IN ALASKA IS GENERATING LARGE SWELL ACROSS THE NE
PACIFIC THIS MORNING. SEAS AT BUOY 4 WHICH IS OFF OF THE NORTHERN
B.C. COAST IS REPORTING 17 FT SEAS AND BUOY 36 WHICH IS OFF THE
SOUTHERN B.C. COAST HAS 13 FT SEAS. THESE SEAS ARE RUNNING AROUND
2 FT ABOVE ENP GUIDANCE. A SIMPLE SWELL DECAY MODEL SUGGESTS THAT
THE SEAS WILL BE AROUND 10 FT AS THEY REACH NORTHERN OREGON WATERS
WHICH IS AROUND 1 FT ABOVE GUIDANCE. THEREFORE EXPECT A BRIEF
PERIOD OF 10 TO 11 FT SWELL TO MOVE THROUGH THE WATERS WEDNESDAY
AFTERNOON AND EVENING.

SURFACE HIGH PRESSURE WILL BUILD OVER THE WATERS THURSDAY AS LOW
PRESSURE SITS OVER NORTHERN CA AND NORTHERLY WINDS WILL DEVELOP
OVER THE WATERS BY FRIDAY. TJ

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
PZ...SMALL CRAFT ADVISORY FOR WINDS UNTIL 4 PM PDT THIS AFTERNOON FOR

     COASTAL WATERS FROM CAPE SHOALWATER WA TO CASCADE HEAD OR
     OUT 10 NM.

     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 6 PM PDT THIS
     EVENING FOR COASTAL WATERS FROM CAPE SHOALWATER WA TO
     CASCADE HEAD OR OUT 10 NM.

     SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR FROM 5 PM
     THIS AFTERNOON TO 10 PM PDT THIS EVENING.

     SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR FROM 6 AM TO
10 AM PDT
     WEDNESDAY.

&&

$$

INTERACT WITH US VIA SOCIAL MEDIA
WWW.FACEBOOK.COM/NWSPORTLAND
WWW.TWITTER.COM/NWSPORTLAND

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.



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