Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 300508
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
907 PM PST THU JAN 29 2015

.SYNOPSIS...A BUILDING UPPER RIDGE WILL MOVE IN FOR MILD AND DRY
WEATHER OVER SOUTHWEST WASHINGTON AND NORTHWEST OREGON THROUGH
FRIDAY AND SATURDAY WITH GOOD RADIATIONAL CONDITIONS FOR AREAS OF
FOG FORMATION BENEATH A STRENGTHENING TEMPERATURE INVERSION.
MODERATE EASTERLY GRADIENTS ALONG THE GORGE THROUGH SATURDAY WILL
PRODUCE SOME AREAS OF EAST WINDS AND DISRUPT THE FOG SOME AROUND THE
COLUMBIA RIVER AND GIVE SOME AREAS OF CLEARING IN THE AFTERNOONS IN
THE VALLEYS. THE NEXT DECENT CHANCE OF RAIN IS SUNDAY AND MONDAY
INTO TUESDAY AS A PAIR OF SYSTEMS MOVE THROUGH.
&&

.UPDATE...A FEW PATCHES OF FOG/STRATUS REMAINED THIS EVENING ALONG
THE CASCADE FOOTHILLS OF LINN AND LANE COUNTY. OTHERWISE...SKIES
CLEARED OUT THIS AFTERNOON AND REMAIN SO AT THIS HOUR. A WEAK
SURFACE THERMAL TROUGH HAS BUILT NORTHWARD ALONG THE CENTRAL OREGON
COAST WITH A STRONGER CORE OVER THE NORTHERN CALIFORNIA AND INTO SW
OREGON. THIS HAS BROUGHT A BIT OF A NORTHERLY PRESSURE GRADIENT TO
THE WILLAMETTE VALLEY AND HAS KEPT NORTHERLY WINDS GOING. ALONG WITH
LOWERING DEW POINTS...THE WINDS HAVE DELAYED THE FOG DEVELOPMENT
TONIGHT FOR THE VALLEY AND AM GIVING IT ABOUT A 30 PERCENT CHANCE OF
BLOCKING SIGNIFICANT DEVELOPMENT UNTIL ABOUT DAYBREAK FRIDAY. THAT
STILL MEANS ITS MORE LIKELY (70%) TO PRODUCE AT LEAST AREAS OF FOG
THROUGHOUT THE NIGHT. ALL THAT SAID...DID OPT TO LIMIT THE CENTRAL
AND SOUTH VALLEY WIDESPREAD FOG MENTION UNTIL MUCH LATER OVERNIGHT
AND ALSO TRIMMED THE AREA FOR EARLY TOMORROW MORNING. CONTINUING ON
THAT THEME OF A LESSER FOG EVENT TONIGHT AND TOMORROW...DID BUMP UP
SOUTH VALLEY TEMPERATURES A SCANT FEW DEGREES OWING TO A BETTER
CHANCE OF FOG/STRATUS BREAKOUT DURING A MEANINGFUL PART OF DAYTIME
HEATING TOMORROW. MAINLY CLEAR SKIES OVER THE LOW CLOUDS SHOULD ALSO
HELP DISSIPATE THE LAYERS FROM THE TOP TOMORROW THOUGH STILL NOT
MUCH GIVEN THE LOWER SUN ANGLE. GRIDDED AND TEXT UPDATES WILL BE
AVAILABLE SHORTLY. /JBONK

&&

.PREV DISC... /ISSUED 201 PM PST THU JAN 29 2015/

SHORT TERM...TONIGHT THROUGH SUNDAY...THE WEAK UPPER DISTURBANCE
THAT SPREAD CLOUDS AND A FEW SPRINKLES ONSHORE LAST NIGHT WAS MOVING
EAST OF THE CASCADES THIS AFTERNOON WITH DECREASING CLOUDS OVER
SOUTHWEST WASHINGTON AND NORTHWEST OREGON. THIS DISTURBANCE
DISRUPTED FOG FORMATION OVERNIGHT. THERE ARE STILL SOME AREAS OF
VALLEY LOW CLOUDS MAINLY SOUTH AND ALONG THE COLUMBIA RIVER THAT ARE
ERODING AND HAVE A GOOD CHANCE OF COMPLETELY CLEARING THIS AFTERNOON.

AN UPPER RIDGE WILL BUILD IN TONIGHT AND EARLY FRIDAY AND CONTINUE
OVER THE PACIFIC NORTHWEST THROUGH SATURDAY. THIS WILL BRING DRY AND
MILD WEATHER TO THE AREA...WITH INCREASING TEMPERATURE INVERSIONS.
THUS THE WARMEST AREAS WILL AND AGAIN BE THE FOOTHILLS AND THE COAST
RANGE. WE WILL SEE MORE AREAS OF VALLEY FOG IN THE NIGHTS AND
MORNINGS AS WELL AS THIS UPPER RIDGE ALSO PROVIDES MUCH BETTER
RADIATIONAL CONDITIONS THE NEXT FEW NIGHTS.

THE EASTERLY GRADIENT THROUGH THE GORGE HAS REACHED 6.5 MB THIS
AFTERNOON...AND WILL LIKELY HANG IN THE 6 TO 7 MB RANGE THROUGH
SATURDAY. THIS WILL KEEP DECENT EAST WINDS THROUGH THE GORGE...WITH
GUSTS AT THE WINDIER AREAS UP AROUND 50 MPH AND NEAR CROWN POINT 60
MPH OR HIGHER. THIS MAY AFFECT THE FOG COVERAGE AROUND THE COLUMBIA
RIVER THE NEXT COUPLE OF DAYS...AND MAY GIVE SOME CLEARING SOUTHWARD
INTO THE WILLAMETTE VALLEY EACH AFTERNOON MORE THAN WE SAW EARLIER
THIS WEEK. VALLEY LOCATIONS THAT CLEAR WILL LIKELY SEE TEMPS UP INTO
THE 50S...AND IF ANY PLACE DOES NOT CLEAR THEN TEMPS WILL BE CLOSER
TO 50 OR THE UPPER 40S.

THE NEXT FRONT PROBABLY IS NOT UNTIL NEXT SUNDAY. THE GFS13 AND THE
ECMWF ARE IN BETTER AGREEMENT NOW THAN THEY HAD BEEN. TOLLESON

LONG TERM...SUNDAY NIGHT THROUGH THURSDAY...NEXT WEEK LOOKS A BIT
MORE ACTIVE THAN THE LAST WEEK OR SO...BUT THERE IS STILL A HINT OF
A FLAT RIDGE ALONG THE WEST COAST THAT LIMITS THE STRENGTH OF ANY
SYSTEMS THROUGH THE FIRST HALF OR SO OF NEXT WEEK. NOT LOOKING FOR
MUCH SNOW TO HELP OUT THE SNOWPACK. THE MODELS HAVE NOT BEEN IN THE
BEST AGREEMENT WITH ANY DETAILS THOUGH THEY ARE COMING TOGETHER
BETTER ON THE GENERAL PATTERN. IT LOOKS LIKE ONE SYSTEM MOVES
THROUGH MONDAY AND MONDAY NIGHT...THEN ANOTHER WEDNESDAY INTO
THURSDAY. IT IS NOT LOOKING AS LIKELY THAT WE WILL GET SIGNIFICANT
ENOUGH RIDGING MID WEEK FOR A SUSTAINED DRY PERIOD THOUGH WE SHOULD
SEE SOME PERIODS OF DRYING BETWEEN THE SYSTEMS. TOLLESON

&&

.AVIATION...CLEAR SKIES AND A MOIST LOWER ATMOSPHERE SHOULD ALLOW
FOG AND LOW STRATUS TO REDEVELOP LATE TONIGHT IN THE INTERIOR
VALLEY. HOWEVER...IF THE WINDS REMAIN STRONG ENOUGH...THERE MAY BE
ENOUGH MIXING TO HALT ITS DEVELOPMENT TILL EARLY FRIDAY MORNING.
EXPECT TO SEE VFR CONDITIONS GIVE WAY TO A MIXTURE OF IFR TO MVFR
CIGS AND VIS LATE TONIGHT THROUGH EARLY FRIDAY MORNING. EXPECT FOG
IN THE INTERIOR VALLEY TO DISSIPATE BETWEEN 18-21Z FRIDAY WITH
CONDITIONS RETURNING TO VFR. THE EXCEPTION TO THIS WILL BE NEAR
THE COLUMBIA RIVER GORGE WHERE STRONG EAST WINDS SHOULD PREVENT
ANY FOG DEVELOPMENT TONIGHT. AS SUCH...KTTD CAN EXPECT TO SEE VFR
CONDITIONS CONTINUE THROUGH FRIDAY EVENING. PATCHY FOG ALONG THE
COAST COULD BRING SOME MVFR CIGS AND VIS TO THE COASTAL TAF SITE
THROUGH EARLY FRIDAY MORNING.

KPDX AND APPROACHES...VFR CONDITIONS UNDER MOSTLY CLEAR SKIES WILL
CONTINUE TONIGHT. THERE IS A SLIGHT CHANCE THAT FOG AND LOW
STRATUS MAY REDEVELOP BRINGING IFR TO MVFR CIGS AND VIS EARLY
FRIDAY MORNING AS THE WINDS EASE SLIGHTLY. HOWEVER...IF THE EAST
WINDS MAKE IT TO THE TERMINAL WE CAN EXPECT TO SEE VFR CONDITIONS
CONTINUE. IF FOG DOES DEVELOP EXPECT IT TO CLEAR BY LATE FRIDAY
MORNING. /64

&&

.MARINE...NO SIGNIFICANT CHANGES...PREVIOUS DISCUSSION
FOLLOWS...HIGH PRESSURE CONTINUES TO BUILD OVER THE WATERS
TONIGHT AND WILL PERSIST THROUGH THE END OF THE WEEK. WINDS HAVE
BECOME MORE NORTHERLY IN RESPONSE TO A COASTAL LOW PRESSURE
BUILDING NORTH UP THE COAST INTO CENTRAL OREGON. GUSTS HAVE
INCREASED TO 25 KT OVER SOUTHERN OREGON WATERS BUT EXPECT THEM TO
REMAIN 20 KT OR LESS OVER CENTRAL OREGON WATERS...WITH STRONGEST
GUSTS S OF NEWPORT. WINDS TURN SOUTHERLY ON SUN AHEAD OF AN
APPROACHING FRONTAL SYSTEM...THE FIRST OF A FEW THAT WILL TRAVERSE
THE WATERS EARLY NEXT WEEK. EACH WILL BRING THE POTENTIAL FOR
SMALL CRAFT WINDS AT TIMES THROUGH AT LEAST THE FIRST HALF OF NEXT
WEEK. SEAS HOLD AROUND 5 FT TODAY...AND WILL BUILD AT TIMES WITH
INCREASING WINDS AND PASSING FRONTS...BUT SHOULD REMAIN BETWEEN 5
FT AND 8 FT THROUGH AT LEAST SUN. MODELS SUGGEST A MORE ACTIVE
PATTERN NEXT WEEK WITH A SERIES OF SYSTEMS...BUT NONE PARTICULARLY
STRONG THROUGH AT LEAST THE MIDDLE OF NEXT WEEK. CULLEN

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
PZ...NONE.

&&

$$

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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