Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 192302 CCB
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
252 PM PST FRI DEC 19 2014

.SYNOPSIS...SCATTERED SHOWERS WILL CONTINUE TODAY WITH SNOW SHOWERS
IN THE CASCADES. MILD AND VERY WET WEATHER IS EXPECTED THIS WEEKEND
WITH AN ATMOSPHERIC RIVER PATTERN RESULTING IN HEAVY RAIN ACROSS MUCH
OF THE REGION...ESPECIALLY MOUNTAINOUS TERRAIN. THERE IS THE
POTENTIAL FOR SOME FLOODING LATE THIS WEEKEND INTO EARLY NEXT WEEK.
LONGER RANGE MODEL OUTPUT IS SUGGESTING A COLDER AIR MASS WILL SETTLE
OVER THE PACIFIC NORTHWEST LATE NEXT WEEK.

&&

.SHORT TERM...THIS AFTERNOON THROUGH MONDAY...SCATTERED SHOWERS
REMAIN THIS AFTERNOON IN THE WAKE OF AN UPPER TROUGH. WE DID SEE ONE
LIGHTNING STRIKE A BIT BEFORE NOON OVER THE COAST RANGE BUT AT THIS
POINT IT LOOKS LIKE THE THUNDER THREAT HAS ENDED AS ANY FORCING FROM
THE TROUGH HAS MOVED WELL EAST OF THE AREA.

WIDESPREAD STRATIFORM RAIN BEGINS TO MOVE INTO THE AREA LATE TONIGHT
WITH THE ONSET OF WHAT CONTINUES TO LOOK LIKE A RATHER IMPRESSIVE
ATMOSPHERIC RIVER EVENT. ALTHOUGH THE GFS CONTINUES TO DELAY THE 850
MB WESTERLY WIND SHIFT UNTIL SATURDAY EVENING...850 MB WINDS OF
AROUND 50 KT SHOULD ENSURE SIGNIFICANT MOISTURE TRANSPORT. BOTH GFS
AND NAM ARE TRENDING DOWN WITH QPF ON SUNDAY SO DECREASED IT TO SOME
EXTENT...BUT SINCE THAT LOOKS LIKE WHEN THE BEST OROGRAPHIC
ENHANCEMENT WILL OCCUR...DID NOT WANT TO LIMIT IT TOO MUCH. DID BRING
INLAND VALLEY QPF DOWN A BIT THOUGH TO REFLECT LIKELY STRONG RAIN
SHADOW EFFECT FROM THE COAST RANGE. STILL THINK WE COULD SEE RAIN
RATES IN THE HIGHER ELEVATIONS OF 1.5 TO 2 INCHES PER 6 HRS FOR AS
MANY AS 24 HOURS IN A ROW THOUGH. A FEW INCHES OF SNOW FELL TODAY ON
MOUNT HOOD AND PROBABLY SOME OF THE OTHER AREA PEAKS BUT SNOW PACK IS
GENERALLY MINIMAL RIGHT NOW. DESPITE LOW SNOW PACK...LATEST HYDRO
GUIDANCE SUGGESTS SOME RIVERS WILL REACH FLOOD STAGE. PLEASE REFER TO
HYDROLOGY SECTION AND CURRENT FLOOD WATCH FOR MORE DETAILS.

HAVE BEEN DEBATING COASTAL WINDS FOR SATURDAY QUITE A BIT WITH NAM
SHOWING BOUNDARY LAYER WINDS RIGHT AROUND 50 KT EARLY SATURDAY
MORNING. HOWEVER THE GFS PEAKS AT 40 TO 45 KT FOR BOUNDARY LAYER
WINDS AND THE ECM IS EVEN LOWER. DECIDED TO NOT ISSUE ANY HIGH WIND
PRODUCTS FOR BEACHES AND HEADLANDS AT THIS POINT AND WILL INSTEAD LET
THE INCOMING SHIFT REASSESS BASED ON NEW MODEL DATA THIS EVENING. IF
HIGH WINDS WERE TO OCCUR...IT LOOKS LIKE THEY WOULD BE SATURDAY
MORNING AND BEACHES AND HEADLANDS COULD GUST UP TO 60 TO 65
MPH...WHICH WOULD MAKE IT A FAIRLY MARGINAL EVENT.

FINALLY...RAPIDLY BUILDING SEAS WILL BRING THE POTENTIAL FOR
DANGEROUS HIGH SURF ALONG THE BEACHES BEGINNING AS EARLY AS LATER
TODAY. COASTAL VISITORS ARE ENCOURAGED TO STAY OUT OF THE SURF ZONE
AS LONG PERIOD SWELLS WILL REACH SHORE AND MAY SURPRISE INDIVIDUALS
WHO ARE UNAWARE. IN ADDITION...LARGE WAVES MAY WASH OVER BEACHES AND
JETTIES WITH LITTLE WARNING. SOME POTENTIAL EXISTS FOR MINOR TIDAL
OVERFLOW SUNDAY AND MONDAY...ESPECIALLY AROUND HIGH TIDES. THIS
THREAT COULD BE ENHANCED BY HIGH FLOWS ON RIVERS IN RESPONSE TO THE
RAINFALL THIS WEEKEND.

THE ATMOSPHERIC RIVER SPIGOT LOOKS LIKE IT FINALLY SHUTS OFF SUNDAY
NIGHT WITH DECREASING POPS INTO MONDAY AS HIGH PRESSURE PUSHES INTO
THE AREA FROM OFF THE CALIFORNIA COAST. HOWEVER RIVER FLOODING MAY
CONTINUE TO BE A THREAT AS THE SIGNIFICANT WEEKEND PRECIP DRAINS DOWN
FROM THE HIGHER TERRAIN. BOWEN/WISHAAR

&&

.LONG TERM...MONDAY NIGHT THROUGH FRIDAY...AN UPPER LEVEL RIDGE WILL
AMPLIFY OVER THE REGION LATE MONDAY INTO TUESDAY. EXTENDED MODELS
AGREE ON A WEAK SHORTWAVE ATTEMPTING TO FLATTEN THE RIDGE TUESDAY
MORNING AS AN UPPER LEVEL TROUGH BEGINS TO DEEPEN IN THE GULF OF
ALASKA. CLOUDY AND RAINY CONDITIONS WILL LINGER INTO THE MIDDLE OF
NEXT WEEK AS THIS DIRTY RIDGE REMAINS OVER THE AREA. THE NEXT MORE
SIGNIFICANT SYSTEM ARRIVES LATE WEDNESDAY AFTERNOON AS THE UPPER
LEVEL TROUGH AXIS BECOMES MORE NEGATIVELY TILTED AND STARTS TO SHIFT
INLAND. THIS MARKS THE NEXT BEST SHOT FOR THE CASCADES TO FINALLY
SEE SOME SNOW ACCUMULATIONS...AS SNOW LEVELS DROP TO 2000-2500 FT
THROUGH CHRISTMAS DAY. HOLIDAY TRAVELERS HEADED OVER THE CASCADE
PASSES WILL CERTAINLY NEED TO MONITOR THE FORECAST. COLDER NORTH
FLOW WILL FOLLOW AND ALLOW TEMPERATURES TO COOL WELL BELOW NORMAL AS
CONDITIONS DRY OUT NEXT FRIDAY. /27

&&

.HYDROLOGY...CONFIDENCE CONTINUES TO INCREASE THAT A SIGNIFICANT
ATMOSPHERIC RIVER TYPE PRECIPITATION EVENT WILL IMPACT SOUTHWEST
WASHINGTON AND NORTHWEST OREGON OVER THE WEEKEND AND INTO EARLY NEXT
WEEK. PRECIPITATION WILL START LATE TONIGHT INTO EARLY SAT AS A WARM
FRONT PUSHES ONSHORE. THE BAROCLINIC ZONE WILL THEN STALL OVER THE
REGION LATER SAT AND REMAIN NEARLY STATIONARY INTO EARLY MON.
SIGNIFICANT SUB-TROPICAL MOISTURE WITH A LONG FETCH THAT STRETCHES
ALL THE WAY TO THE SOUTH CHINA SEA WILL FEED INTO THIS FRONTAL
SYSTEM...BRINGING THE LIKELIHOOD OF VERY LARGE RAINFALL TOTALS
ACROSS THE REGION. LOW AND MID LEVEL WINDS WILL SWITCH FROM
SOUTHERLY TO WESTERLY SAT AFTERNOON. THESE STRONG WESTERLY WINDS
WILL CONTINUE INTO EARLY MON...WHICH WILL CREATE SIGNIFICANT
OROGRAPHIC ENHANCEMENT TO THE PRECIPITATION ALONG THE HIGHER TERRAIN
OF THE COAST RANGE...FOOTHILLS...AND CASCADES. THESE AREAS ARE
EXPECTED TO SEE AROUND 6 TO 12 INCHES OVER RAIN THROUGH EARLY
MON...WITH LOCALIZED AREAS SEEING EVEN HIGHER AMOUNTS IN THE N
OREGON CASCADES. THE LOWER TERRAIN IS FORECASTED TO SEE
LOWER...ALTHOUGH STILL IMPRESSIVE TOTALS. WE EXPECT 4 TO 8 INCHES TO
FALL ALONG THE COAST...AND 2 TO 5 INCHES OVER THE INTERIOR LOWLANDS.

BASED ON THE LATEST FORECAST RAINFALL TOTALS...NUMEROUS AREA RIVERS
ARE NOW PROJECTED TO REACH FLOOD STAGE. A FEW LOCATIONS ARE EVEN
PROJECTED TO REACH MAJOR FLOOD STAGE. A FLOOD WATCH HAS BEEN ISSUED
FOR ALL OF SW WASHINGTON AND NW OREGON STARTING LATE SAT AFTERNOON
AND CONTINUING THROUGH MON. SOME OF THE FASTER RESPONDING RIVERS
DRAINING THE COAST RANGE AND CASCADES COULD REACH FLOOD STAGE AS
EARLY AS SAT EVENING. SLOWER RESPONDING AND MAIN STEM RIVERS WOULD
LIKELY NOT REACH FLOOD UNTIL LATER SUNDAY OR EARLY NEXT WEEK.

IN ADDITION TO THE FLOODING CONCERNS...EXCESSIVE RAINFALL HAS THE
POTENTIAL TO CREATE LANDSLIDES...DEBRIS FLOWS...AND EXCESSIVE RUNOFF
IN THE VICINITY OF RECENT WILDFIRE BURN SCARS. BURN SCARS FROM TWO
LARGE FIRES THIS SUMMER...THE 36 PIT FIRE IN THE CLACKAMAS RIVER
BASIN NEAR ESTACADA AND THE DECEPTION COMPLEX NEAR OAKRIDGE...WILL
BE PARTICULARLY VULNERABLE.

AS IS USUALLY THE CASE WITH THESE ATMOSPHERIC RIVER HEAVY
PRECIPITATION EVENTS...A LOT DEPENDS ON EXACTLY WHERE THE BAND OF
SUBTROPICAL MOISTURE SETS UP. THE FCST MODELS HAVE BEEN CONSISTENTLY
HIGHLIGHTING OUR REGION FOR SOME OF THE MOST SIGNIFICANT IMPACTS FOR
THE LAST SEVERAL DAYS. HOWEVER...THERE COULD STILL BE SHIFTS IN THE
EXACT POSITIONING OF THE SYSTEM...WHICH WOULD EFFECT PRECIPITATION
ESTIMATES AND RIVER FORECASTS. PLEASE CONTINUE TO FOLLOW THE LATEST
FORECASTS. RIVER FORECASTS ARE AVAILABLE ON OUR WEB PAGE AT:
HTTP://WATER.WEATHER.GOV/AHPS2/INDEX.PHP?WFO=PQR (ALL LOWER CASE).
PYLE

&&

.AVIATION...A SHOWERY AIRMASS WILL LEAD TO PREDOMINANTLY VFR
CONDITIONS THROUGH THIS EVENING. A WARM FRONT SPREADING WIDESPREAD
LIGHT TO MODERATE RAIN INTO THE AREA OVERNIGHT SHOULD RESULT IN
A DETERIORATION OF CONDITIONS AT ALL TAF SITES AFTER 06Z
SATURDAY. EXPECT WIDESPREAD HIGH END IFR TO MVFR CONDITIONS
BETWEEN 09Z AND 18Z SATURDAY ACROSS NORTHWEST OREGON AND SOUTHWEST
WASHINGTON.

KPDX AND APPROACHES...AN UNSTABLE SHOWERY AIRMASS WILL LEAD TO A
MIX OF VFR AND MVFR CONDITIONS THROUGH 06Z SATURDAY. A WARM FRONT
WILL SPREAD STEADY RAIN INTO THE TERMINAL BETWEEN 09Z AND 18Z
SATURDAY. EXPECT FLIGHT CONDITIONS TO SHIFT MORE SOLIDLY INTO THE
MVFR CATEGORY DURING THIS TIME. /NEUMAN


&&

.MARINE...THE MAIN WEATHER STORY IN THE IMMEDIATE SHORT TERM IS THAT
SEAS CURRENTLY IN THE 10 TO 12 FT RANGE WILL NEARLY DOUBLE IN HEIGHT
TODAY...RISING INTO THE 20 TO 23 FT RANGE WITH A DOMINANT PERIOD
NEAR 18 TO 19 SECONDS. ANY SMALL CRAFT VESSELS ARE URGED TO COME
ONSHORE IMMEDIATELY AS HIGHER SEAS ARE BEGINNING TO ARRIVE. BUOY 89
ABOUT 70 MILES OFFSHORE JUMPED TO 19 FT AT 19 SECONDS AT 2 PM...AND
WILL LIKELY EXCEED 20 FT IN THE NEXT HOUR OR TWO. THESE HIGHER SEAS
WILL PUSH INTO THE INNER COASTAL WATERS BETWEEN 4 AND 6 PM.

PEOPLE SHOULD AVOID WALKING AND CLIMBING ON JETTIES ALONG THE OREGON
AND WASHINGTON COASTS THROUGH SATURDAY...BUT ESPECIALLY THIS
AFTERNOON AND EVENING. THERE IS CONSIDERABLE CONCERN THAT SNEAKER
WAVES WILL RUN UP MUCH FARTHER UP THE BEACH THAN WAVES OBSERVED OVER
THE PREVIOUS 15 TO 30 MINUTES. UNDER SIMILAR SCENARIOS...PEOPLE HAVE
BEEN KILLED BY BEING SWEPT OFF THEIR FEET AND DRAGGED OUT TO SEA BY
THE RECEDING WATER OR BY THE WATER DISLODGING STUCK DRIFTWOOD THAT
SUBSEQUENTLY ROLES OVER AN UNSUSPECTING PERSON. PLEASE BE COGNIZANT
OF THIS WHEN RECREATING ON THE BEACHES OF THE OREGON AND WASHINGTON
COASTS THROUGH SATURDAY.

THE NEXT FRONTAL STORM SYSTEM IS STILL ON TRACK TO IMPACT THE WATERS
LATE TONIGHT AND SATURDAY MORNING. EXPECT WINDS TO GRADUALLY
INCREASE TODAY AND TONIGHT...WITH SOLID GALE FORCE WINDS OF 30 TO 40
KT WITH GUSTS OF 40 TO 45 KT EXPECTED ACROSS THE WATERS BY SATURDAY
MORNING. THERE IS A CHANCE GUSTS MAY APPROACH 50 KT WITHIN 20 NM OF
THE COAST AS A SHORT LIVED COASTAL JET DEVELOPS...PARTICULARLY ALONG
THE CENTRAL OREGON COAST. THE GALE WARNING FOR THE INNER WATERS MAY
NEED TO BE UPGRADED TO A STORM WARNING...BUT WILL LET SUBSEQUENT
SHIFTS DIGEST ADDITIONAL MODEL RUNS BEFORE MAKING THE CALL.

WHILE THE AFOREMENTIONED LARGE WESTERLY SWELL WILL SLOWLY SUBSIDE
SATURDAY...THIS RENEWED SHOT OF STRONG WINDS ACROSS THE WATERS ON
SATURDAY MORNING...WILL LIKELY KEEP SEAS FLIRTING WITH 20 FT MARK
FOR MUCH OF THE DAYLIGHT HOURS ON SATURDAY. EXPECT THE HIGHEST WINDS
TO TAPER AROUND MIDDAY OR EARLY SATURDAY AFTERNOON...WHICH WILL THEN
ALLOW COMBINED SEAS TO BEGIN SUBSIDING. HOWEVER...ADDITIONAL GUSTS
OF 35 KT MAY LINGER ACROSS THE WATERS INTO SATURDAY EVENING AS
ANOTHER WEAK SURGE OF WINDS ENTERS THE WATERS. THE GALE WARNING FOR
LATE TONIGHT AND SATURDAY MORNING WAS EXTENDED INTO SATURDAY EVENING
TO COVER THIS PERIOD...BUT CONFIDENCE IS CONSIDERABLY LOWER THAT
THESE 35 KT WIND GUSTS WILL OCCUR LATE SATURDAY AFTERNOON AND
EVENING. AGAIN...THE PRIMARY WINDOW OF CONCERN FOR THE HIGHEST WINDS
ACROSS THE WATERS WILL BE SATURDAY MORNING...AND CONFIDENCE IS HIGH
THEY WILL OCCUR.

SOUTHWESTERLY TO WESTERLY WINDS WILL CONTINUE INTO SUNDAY...KEEPING
SEAS WELL IN THE TEENS THROUGH SUNDAY NIGHT. SEAS MAY TEMPORARILY
BOTTOM OUT NEAR 10 FT EARLY NEXT WEEK BEFORE A WEAK FRONT...AND
ACCOMPANYING LARGER WESTERLY SWELL AROUND 15 FT SLIDES INTO THE
WATERS TOWARDS MIDWEEK.

HIGH TIDE NEAR TOKE POINT IS EXPECTED TO FLIRT WITH 11 FT ON
SATURDAY DUE TO A TIDAL ANOMALY NEAR 1 FT. HOWEVER...THE HEAVIEST
RAIN WILL NOT HAVE ARRIVED TO ALLOW THE FLOWS ON THE WILLAPA AND
NASELLE RIVERS TO INCREASE ENOUGH THAT MINOR TIDAL OVERFLOW FLOODING
WILL BE A CONCERN. WHILE THE TIDAL ANOMALY WILL LIKELY BE SLIGHTLY
LESS ON SUNDAY...THE SUBSTANTIAL INCREASE IN RIVER FLOWS EXPECTED ON
THE WILLAPA AND NASELLE RIVERS INCREASE OUR CONCERN ON MINOR TIDAL
OVERFLOW FLOODING OCCURRING AROUND THE TOWNS OF RAYMOND...NASELLE
AND OTHER LOW LYING SPOTS AROUND WILLAPA BAY WASHINGTON. IN
FACT...BY MIDDAY SUNDAY...SEVERAL OREGON COASTAL RIVERS WILL LIKELY
BE NEAR FLOOD STAGE OR EXCEEDING FLOOD STAGE SO COASTAL FLOOD
CONCERNS WILL LIKELY ENCOMPASS MUCH OF THE COAST. DUE TO THE RIVERS
REMAINING HIGH AND HIGH TIDAL CYCLES CONTINUING...THESE TIDAL
OVERFLOW CONCERNS COULD CERTAINLY LINGER INTO MONDAY. EXPECT THESE
ISSUES TO BE MOST PREVALENT BETWEEN 9 AM AND 3 PM ON SUNDAY/MONDAY.
/NEUMAN


&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...FLOOD WATCH FROM SATURDAY AFTERNOON THROUGH MONDAY AFTERNOON FOR

     CASCADE FOOTHILLS IN LANE COUNTY-CASCADES IN LANE COUNTY-
     CENTRAL COAST RANGE OF WESTERN OREGON-CENTRAL COLUMBIA
     RIVER GORGE-CENTRAL OREGON COAST-CENTRAL WILLAMETTE VALLEY-
     COAST RANGE OF NORTHWEST OREGON-GREATER PORTLAND METRO AREA-
     LOWER COLUMBIA-NORTH OREGON COAST-NORTHERN OREGON CASCADE
     FOOTHILLS-NORTHERN OREGON CASCADES-SOUTH WILLAMETTE VALLEY-
     UPPER HOOD RIVER VALLEY-WESTERN COLUMBIA RIVER GORGE.

     HIGH SURF ADVISORY UNTIL 4 PM PST SATURDAY FOR CENTRAL OREGON
     COAST-NORTH OREGON COAST.

WA...FLOOD WATCH FROM SATURDAY AFTERNOON THROUGH MONDAY AFTERNOON FOR

     CENTRAL COLUMBIA RIVER GORGE-GREATER VANCOUVER AREA-I-5
     CORRIDOR IN COWLITZ COUNTY-SOUTH WASHINGTON CASCADE
     FOOTHILLS-SOUTH WASHINGTON CASCADES-SOUTH WASHINGTON COAST-
     WESTERN COLUMBIA RIVER GORGE-WILLAPA HILLS.

     HIGH SURF ADVISORY UNTIL 4 PM PST SATURDAY FOR SOUTH WASHINGTON
     COAST.

     WINTER WEATHER ADVISORY UNTIL 1 PM PST SATURDAY FOR SOUTH
     WASHINGTON CASCADES.

PZ...SMALL CRAFT ADVISORY FOR WINDS UNTIL 1 AM PST SATURDAY FOR
     COASTAL WATERS FROM CAPE SHOALWATER WA TO FLORENCE OR OUT 60 NM.

     GALE WARNING FROM 1 AM TO 9 PM PST SATURDAY FOR COASTAL WATERS
     FROM CAPE SHOALWATER WA TO FLORENCE OR OUT 60 NM.

     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 1 AM PST SATURDAY
     FOR COASTAL WATERS FROM CAPE SHOALWATER WA TO FLORENCE OR OUT 60
     NM.

     SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR UNTIL 4 PM PST
     SUNDAY.

&&


$$

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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