Area Forecast Discussion
Issued by NWS Portland, OR

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000
FXUS66 KPQR 260511
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
909 PM PST TUE NOV 25 2014

.SYNOPSIS...A WARM FRONTAL BOUNDARY OVER WESTERN WASHINGTON WILL
CONTINUE TO LIFT NORTH TONIGHT AND WEDNESDAY. HIGH PRESSURE ALOFT
WEDNESDAY SHOULD BE STRONG ENOUGH TO KEEP MOST OF THE AREA
DRY...EXCEPT FOR SW WASHINGTON. THE NEXT WEATHER SYSTEM REACHES THE
COAST LATE WED EVENING AND THEN MOVES INLAND OVERNIGHT AND INTO
THANKSGIVING MORNING. MUCH COOLER AIR ASSOCIATED WITH THE NORTHERN
BRANCH OF THE JET STREAM IS FORECAST TO SPREAD OVER THE AREA THIS
WEEKEND...FOR ANOTHER ROUND OF EAST WIND IN THE COLUMBIA RIVER GORGE.
SNOW LEVELS WILL LOWER DRAMATICALLY THIS WEEKEND...BUT SLOWLY RISE
EARLY NEXT WEEK.

&&

.UPDATE...RADAR SHOWS LIGHT RAIN...MOSTLY OROGRAPHICALLY
INDUCED...OVER THE COAST RANGE AND SOUTH WASHINGTON AND NORTH OREGON
CASCADES...WITH RAIN RATES OF ONLY A FEW HUNDREDTHS OF AN INCH PER
HOUR. AS RIDGING BUILDS INTO THE AREA FROM THE SOUTH...RAIN WILL
TAPER OFF THROUGH WEDNESDAY. EXPECT THE WILLAMETTE VALLEY TO REMAIN
DRY THROUGH THE OVERNIGHT HOURS AND INTO WEDNESDAY. WITH CLEARING
SKIES PARTICULARLY IN THE SOUTH AND CENTRAL WILLAMETTE
VALLEY...SHOULD SEE SOME FOG LATER TONIGHT AND WEDNESDAY MORNING BUT
ANY VISIBILITY BELOW ABOUT 1/2 MILE SHOULD BE ISOLATED. FOR THE
FORECAST UPDATE...TOOK OUT POPS FOR TONIGHT AND WEDNESDAY IN THE
WILLAMETTE VALLEY AND TAPERED RAIN CHANCES ELSEWHERE OFF SLIGHTLY
FASTER. ALSO RAISED HIGH TEMPERATURES WEDNESDAY A COUPLE OF DEGREES
BASED ON TODAY`S OBSERVED HIGHS AND A PERSISTENT PATTERN.
FINALLY...HAVE INCREASED WINDS ALONG THE COAST TOMORROW NIGHT BASED
ON LATEST MODELS. EXPECT WINDY BUT SUB-WARNING CONDITIONS. BOWEN

.SHORT TERM (PREVIOUS DISCUSSION)...TONIGHT THROUGH FRIDAY...500 MB
RIDGE REMAINS CENTERED ALONG 130W WITH A BAROCLINIC ZONE RIDING OVER
THE TOP. KLGX RADAR INDICATING RETURNS OVER MUCH OF SW WA.
HOWEVER...ECHO INTENSITY HAS DIMINISHED AND THIS IS EVIDENT IN THE
LATEST 6-HR PRECIP AMOUNTS. RAINFALL RATES AS OF 21Z IN THE SW WA
CASCADES AND FOOTHILLS HAVE EASED TO AROUND ONE TENTH OR LESS. 24-HR
TOTALS GENERALLY 1 TO 3 INCHES...WITH SOME SNOTELS COMING IN WITH 3.5
INCHES. 500 MB HEIGHTS NEAR 570 DM COMBINED WITH 1000-500 MB
THICKNESS VALUES IN THE MID TO UPPER 550S AND 850 MB TEMPS 8-10C HAVE
RESULTED IN NEAR-RECORD DAYTIME TEMPERATURES IN THE WILLAMETTE
VALLEY. THE MILD AIR MASS WILL BE CONDUCING TO VALLEY FOG FORMATION
TONIGHT...ESPECIALLY WITH THE RELATIVELY HIGH DEW POINTS. FOG WILL
FAVOR THE SOUTH HALF OF THE AREA WHERE LESS CLOUD COVER IS EXPECTED.

THE THANKSGIVING FRONT IS STILL ON TRACK TO REACH THE COASTLINE LATE
WED EVENING THEN MIGRATE INLAND OVERNIGHT AND THANKSGIVING MORNING.
THE REMNANTS OF THE FRONTAL BOUNDARY STALL ACROSS THE INTERIOR
VALLEYS AND CASCADES THANKSGIVING NIGHT. THE GFS AND ECMWF HANDLE THE
QPF FIELD VALID 06Z FRI QUITE DIFFERENTLY. THE GFS SHOWS AN OBVIOUS
BREAK IN THE FRONTAL BOUNDARY...WITH SEPARATE QPF BULLS-EYES OVER FAR
SW OREGON AND ALSO IN THE S WA CASCADES AND FOOTHILLS. THE ECMWF SHOW
A MUCH LARGER SRN QPF AREA EXTENDING FURTHER N...TO THE CENTRAL
INTERIOR VALLEYS AND CASCADES. BY 12Z FRI THE ECMWF HAS A BROAD SWATH
OF QPF OVER THE ENTIRE FORECAST AREA WHILE THE GFS MAINTAINS THE TWO
SEPARATE AND DISTANT CORES. IN ANY EVENT...THE AIR MASS WILL REMAIN
QUITE MILD THROUGH THU NIGHT WITH SNOW LEVELS WELL
ABOVE THE CASCADE PASSES.

THINGS START TO CHANGE FRI AS BOTH THE ECMWF AND GFS SHOW THE
NORTHERN AND SOUTHERN JET STREAM BRANCHES PHASING TOGETHER. BOTH
MODELS HAVE A MUCH COLDER CANADIAN AIR MASS SAGGING S THROUGH NRN WA
FRI. MODELS DEVELOP AN AREA OF ENHANCED QPF ALONG THE REMNANT FRONTAL
BOUNDARY. THE EXACT LOCATION OF THIS BOUNDARY REMAINS IN QUESTION.
THE GFS HAS IT ALONG A LINE FROM NEWPORT TO ALBANY WHILE THE ECMWF
HAS IT A BIT MORE NORTH BUT WITH LESSER AMOUNTS. WEISHAAR

.LONG TERM...FRIDAY NIGHT THROUGH TUESDAY...COMPLICATED PATTERN
EVOLVES FRIDAY NIGHT AND SAT WITH THE COLDER AIR CONTINUING TO SLIDE
S THROUGH WA AND INTO NRN OREGON. 12Z GFS MORE IN LINE WITH THE
PREVIOUS COUPLE OF ECMWF RUNS...DEPICTING A COLD AIR WEDGE IN THE
CENTRAL COLUMBIA GORGE BY 00Z SUN. LOOK FOR THE EAST WIND TO RETURN
AS WELL...BEGINNING SAT MORNING AND CONTINUING THROUGH THE WEEKEND.
BY 00Z SUN THE GFS HAS -8 TO -10C 850 MB AIR IN THE CENTRAL COLUMBIA
GORGE...WHILE THE ECMWF IS JUST A TOUCH WARMER. FORTUNATELY...THE
DRIER NLY FLOW WILL SHUNT PRECIP FURTHER TO THE S. A CLOSED LOW WELL
OF THE NRN CA COAST SAT STARTS TO DRIFT NE SAT NIGHT AND SUN. THERE
IS THE POTENTIAL FOR A DEFORMATION BAND OVER NRN CA TO DRIFT NWD LATE
SUN INTO MON. THIS COULD BE PROBLEMATIC AS THE MOISTURE OVERRUNS THE
COLD AIR....ESPECIALLY FOR THE COLUMBIA GORGE AND UPPER HOOD RIVER
VALLEY. WEISHAAR

&&

.AVIATION...CONDITIONS HAVE DRAMATICALLY IMPROVED OVER THE LAST
COUPLE HOURS FOR THE INLAND LOCATIONS WHILE THE COAST HAS LARGELY
REMAINED IFR OR WORSE THIS EVENING. MODELS HAVE NOT BEEN HANDLING
THE SITUATION WELL AT ALL AS ABUNDANT LOW LEVEL MOISTURE HAS
REMAINED. THE UPPER RIDGE WILL CONTINUE TO BUILD AS IT TRANSITS
THE REGION WITH SURFACE WINDS ON DECREASING. DEW POINTS ARE IN
THE 50S AT THIS HOUR BUT SHOULD LOWER SOME THIS EVENING. HAVE
DOUBTS DEW POINTS WILL BE ABLE TO KEEP AHEAD OF TEMPERATURES AND
EXPECT TO SEE FOG DEVELOP. CONFIDENCE IS FAR TOO
LOW...HOWEVER...FOR SPECIFIC AREAS AND DECIDED AGAIN INCLUSION IN
THE TAF PACKAGES ASIDE FROM KSLE AND KEUG. REGARDLESS...HAVE
REASONABLE CONFIDENCE LOW STRATUS WILL DEVELOP INLAND WHERE FOG
DOESN`T. DONT EXPECT MUCH IMPROVEMENT ABOVE IFR UNTIL PERHAPS
AFTER 19-21Z.

KPDX AND APPROACHES...VFR CIGS CURRENTLY BUT EXPECT LOW CLOUDS TO
BREAK UP SOME WITH ENOUGH CLEARING ALLOWING FOR A LOWER STRATUS
DECK TO DEVELOP OVERNIGHT. EXPECT A 015 TO 020 DECK WILL REMAIN
UNTIL AROUND 20Z BEFORE CLEARING OUT THROUGH 27/06Z JBONK

&&

.MARINE...WIND GUSTS ACROSS THE NORTHERN WATERS HAVE STAYED BELOW
SMALL CRAFT CRITERIA WITH THE HRRR MODEL HAVING THE BEST HANDLE
ON THE SITUATION AT THIS TIME. THAT MODEL DOES NOT BRING A THREAT
FOR CRITERIA LEVEL GUSTS BACK UP UNTIL AFTER 5 AM EARLY WEDNESDAY.
AS SUCH HAVE DROPPED THE SMALL CRAFT WIND ADVISORY FOR THE TIME
BEING. SEAS ARE ALSO RUNNING ABOUT A FOOT BELOW GUIDANCE AND THE
FORECAST SO HAVE ALSO LOWERED JUST A BIT.

THE CURRENT SOUTHWEST WINDS WILL BACK TO THE SOUTH AND INCREASE
AS A STRONG FRONT APPROACHES WEDNESDAY AFTERNOON. THIS FRONT WILL
LIKELY PRODUCE GALE FORCE WINDS WEDNESDAY NIGHT WITH THE PREVIOUS
SHIFT HAVING ISSUED A GALE WARNING.

ANOTHER FRONT IS EXPECTED TO BRUSH BY THE SOUTHERN WATERS FRIDAY.
THIS FRONT WILL APPROACH FROM THE SW AND THE MODELS VARY ON HOW
FAR NORTH IT WILL REACH...AND ON THE TIMING. THEREFORE...THERE IS
LOW CONFIDENCE FOR FRIDAY FORECAST. A LARGE LOW WILL DROP SOUTH
FROM THE GULF OF ALASKA FRIDAY AND SETTLE SW OF THE WATERS THIS
WEEKEND...AND GENERATE OFFSHORE WINDS THROUGH THE WEEKEND. THESE
WINDS WILL LIKELY RESULT IN ENHANCED GUSTS NEAR THE COASTAL
GAPS...POSSIBLY NEEDING A WIND HEADLINE. JBONK/TJ

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
PZ...SMALL CRAFT ADVISORY FOR WINDS FROM 4 AM TO 4 PM PST WEDNESDAY
     FOR COASTAL WATERS FROM CAPE SHOALWATER WA TO CASCADE HEAD OR
     OUT 60 NM.

     GALE WARNING FROM 4 PM WEDNESDAY TO 4 AM PST THURSDAY FOR
     COASTAL WATERS FROM CAPE SHOALWATER WA TO FLORENCE OR OUT 60 NM.

     SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR FROM 5 AM TO 9
     AM PST WEDNESDAY.

     SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR FROM 4 PM TO
     10 PM PST 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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