Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 261040
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
240 AM PST MON JAN 26 2015

.SYNOPSIS...A STRONG RIDGE OF HIGH PRESSURE ALOFT WILL CONTINUE TO
MOVE AWAY TO THE E TODAY...WEAKENING THE LOW LEVEL INVERSION LATER
TODAY. A VERY WEAK FRONTAL SYSTEM WILL APPROACH THE COAST LATE
TONIGHT...THEN LINGER OVER NW OREGON AND SW WA THROUGH WED. ANOTHER
RIDGE OF HIGH PRES IS EXPECTED TO DEVELOP OVER THE PACIFIC NW LATE
IN THE WEEK AND CONTINUE INTO THE WEEKEND.
&&

.SHORT TERM...SURFACE OBSERVATIONS AND SATELLITE FOG CHANNEL IMAGERY
INDICATED AN AREA OF WIDESPREAD FOG AND LOW STRATUS EXTENDING FROM
THE I-5 CORRIDOR IN SW WA S THROUGH THE LOWER COLUMBIA AND
WILLAMETTE VALLEYS EARLY THIS MORNING. AS WAS SEEN RATHER
DRASTICALLY IN THE 00Z SLE SOUNDING SUN AFTERNOON...A VERY STRONG
INVERSION WAS THE CAUSE OF THE FOG TRAPPED IN THE LOWER VALLEYS
WHILE ABOVE ABOUT 1K FT CONDITIONS WERE MUCH WARMER AND DRIER. WATER
VAPOR PICTURES EARLY THIS MORNING SHOWED THE UPPER RIDGE WAS STILL
IN PLACE OVER OREGON FOR CONTINUED STABLE CONDITIONS...BUT MODELS
ALL EXPECT THE RIDGE AXIS TO MOVE RAPIDLY E TODAY WHICH WILL RESULT
IN A WEAKENING INVERSION. MANY AREAS WERE STILL REPORTING
VISIBILITES AT OR BELOW A QUARTER MILE...SO WILL CONTINUE WITH THE
DENSE FOG ADVISORY THIS MORNING. ALTHOUGH THE INVERSION WEAKENS
TODAY...IT STILL MAY NOT BE ENOUGH TO BREAK UP THE INLAND STRATUS
EVERYWHERE SO ANOTHER RELATIVELY COOL DAY CAN BE EXPECTED IN THE
INTERIOR VALLEYS...WITH WARMER ALTOUGH NOT QUITE SO WARM TEMPS AT
HIGHER ELEVATIONS.

WITH THE WEAKENING OF THE INLAND SURFACE HIGH TODAY...MODELS
GENERALLY AGREE ON A SWITCH TO SSW ONSHORE WINDS ALONG THE COAST
TODAY. THIS WILL MODERATE TEMPS ON THE COAST TODAY...AND WILL
ULTIMATELY PUSH SOME MARINE CLOUDS ONTO THE COAST AND SLOWLY SPREAD
THEM INLAND TONIGHT. AS THE UPPER RIDGE COLLAPSES...A RATHER FLAT
WESTERLY FLOW DEVELOPS ALOFT TONIGHT AND CONTINUES THROUGH WED.
MODELS REMAIN IN GOOD AGREEMENT IN SHOWING A DECAYING FRONT SAGGING
DOWN INTO THE NW PART OF THE FORECAST AREA LATE TONIGHT AND
LINGERING THROUGH WED. MODEL CROSS SECTIONS INDICATE THERE IS SOME
DEPTH TO THE MOISTURE OVER THE N COASTAL AREAS WITH THIS BAROCLINIC
ZONE...WHILE FURTHER TO THE S AND E MOISTURE BECOMES SHALLOWER. WILL
KEEP CHANCE POPS OVER THE NW PART OF THE AREA FROM LATE TONIGHT
THROUGH WED...AND TAPER OFF ANY CHANCES FOR LIGHT PRECIPITATION
FURTHER TO THE S AND E. THE RETURN TO WEAK ONSHORE FLOW WILL BRING
TEMPS DOWN CLOSER TO SEASONAL NORMALS.

.LONG TERM...NO CHANGES. PREVIOUS DISCUSSION FOLLOWS. WEDNESDAY
NIGHT THROUGH SUNDAY...A PASSING SHORTWAVE LATE WED NIGHT MAY
PROVIDE ENOUGH LIFT FOR A FEW SHOWERS...MOSTLY ALONG THE NORTH COAST
AND COAST RANGE AND INTO SW WASHINGTON. MODELS REMAIN IN GOOD
AGREEMENT THAT A RIDGE OF HIGH PRES ALOFT REBUILDS ON THU AND
PERSISTS THROUGH THE END OF THE WEEK. THIS WILL MAINTAIN DRY
CONDITIONS BUT BRING DAILY FOG AND LOW CLOUDS TO INTERIOR VALLEY
LOCATIONS. THE RIDGE WILL LIKELY BREAK DOWN AND SHIFT INLAND SOME
TIME NEXT WEEKEND...BUT STILL SOME UNCERTAINTY AS TO IF THIS WILL BE
SAT OR SUN. THE 12Z GFS IS A BIT MORE AGGRESSIVE IN BRINGING A MOIST
FRONTAL SYSTEM TO THE REGION BY LATE SAT NIGHT...WHILE THE ECMWF
WOULD KEEP THINGS DRY UNTIL SUN NIGHT. INCREASED POPS A BIT FOR NEXT
WEEKEND...PARTICULARLY FOR THE NW PORTION OF THE FORECAST
AREA...THOUGH RESTRICTED TO LOWER END CHANCE FOR SAT NIGHT THROUGH
SUN GIVEN THE SUPPORT FOR THE LATER TIMING FROM THE ECMWF AND
NUMEROUS GEFS MEMBERS. CULLEN
&&

.AVIATION...HIGH PRESSURE AND A STRONG INVERSION HAVE LED TO MOST
TAF SITES DROPPING DOWN INTO LIFR AND IFR CONDITIONS. EXPECT KEUG
AND KSLE TO EXPERIENCE THESE REDUCTIONS THROUGH A GOOD PORTION OF
THE NEXT 24 HOURS. KHIO MAY ALSO FALL INTO THIS CATEGORY.
HOWEVER...EAST WINDS POURING OUT OF THE COLUMBIA RIVER GORGE ARE
CURRENTLY PRODUCING VFR CONDITIONS AT KPDX AND KTTD. THESE EAST
WINDS SHOULD SUBSIDE TODAY...AND IF THE LIFR/IFR FOG DOES NOT
RETURN TO THESE SITES LATER THIS MORNING...EXPECT REDUCTIONS TO
DEVELOP TONIGHT. A SOUTHERLY WIND REVERSAL IS ALSO PUSHING
NORTHWARD OFFSHORE. STRATUS OFF THE COAST SHOULD PUSH ASHORE LATER
TODAY AND TONIGHT...AND BRING IFR CONDITIONS TO KAST AND KONP.
HOWEVER...MODELS ARE STRUGGLING WITH THE CURRENT PLACEMENT OF IT
RIGHT NOW SO UNCERTAINTY IN THE TIMING OF WHEN THESE REDUCTIONS
WILL OCCUR IS HIGH.

KPDX AND APPROACHES...LIGHT EAST WINDS POURING OUT OF THE COLUMBIA
RIVER GORGE CONTINUE TO BRING A MIX OF VFR AND LIFR CONDITIONS TO
THE TERMINAL. EXPECT THE EAST WINDS TO DOMINATE FOR THE NEXT
SEVERAL HOURS...BUT A GRADUAL WEAKENING OF THE HIGH PRESSURE EAST
OF THE CASCADES SHOULD ALLOW IFR CONDITIONS TO RETURN LATER THIS
MORNING. HOWEVER...CONSIDERABLE UNCERTAINTY EXISTS IN THE TIMING
OF WHEN THE SWITCHES FROM VFR TO LIFR/IFR WILL OCCUR. /NEUMAN

&&

.MARINE...A SOUTHERLY WIND SURGE IS CURRENTLY UNDERWAY AND MAY
LEAD TO BRIEF PERIOD THIS MORNING OF WIND GUSTS AROUND 20 KT
ACROSS THE WATERS. OTHERWISE...A WEAK FRONT DROPPING SOUTHEASTWARD
WILL BRING A WIND SHIFT TO THE WATERS ON TUESDAY...BUT HAVE
LITTLE APPRECIABLE IMPACTS TO MARINE INTERESTS. HIGH PRESSURE IS
THEN EXPECTED TO BUILD BACK OVER THE WATERS LATE IN THE WORK WEEK
WITH LIGHT WINDS CONTINUING. SEAS WILL GENERALLY SUBSIDE DURING
THIS TIME...AND END UP WELL BELOW 10 FT. THERE IS A DECENT CHANCE
A MORE ACTIVE STORM PATTERN WILL DEVELOP LATE IN THE WEEKEND AND
NEXT WEEK SO EXPECT SEAS AND WINDS TO INCREASE. /NEUMAN

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...DENSE FOG ADVISORY UNTIL 11 AM PST THIS MORNING FOR CENTRAL
     WILLAMETTE VALLEY-GREATER PORTLAND METRO AREA-LOWER
     COLUMBIA-SOUTH WILLAMETTE VALLEY.

WA...DENSE FOG ADVISORY UNTIL 11 AM PST THIS MORNING FOR GREATER
     VANCOUVER AREA-I-5 CORRIDOR IN COWLITZ COUNTY.

PZ...SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR FROM 7 AM
     THIS MORNING TO NOON PST TODAY.
&&

$$

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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