Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 210430
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
830 PM PST SAT DEC 20 2014

.SYNOPSIS...MILD AND VERY WET WEATHER IS EXPECTED TO CONTINUE OVER
SOUTHWEST WASHINGTON AND NORTHWEST OREGON THROUGH SUNDAY AS A STRONG
WESTERLY FLOW TRANSPORTS A PLUME OF TROPICAL MOISTURE INTO THE AREA.
THE HEAVIEST RAIN WILL BE OVER THE MOUNTAINS...AND SHOULD EASE SOME
LATE SUNDAY IN TO MONDAY. THERE IS THE STRONG POTENTIAL FOR RIVER
FLOODING FROM TONIGHT INTO EARLY NEXT WEEK. LONGER RANGE MODEL
OUTPUT IS SUGGESTING A COLDER AIR MASS WILL SETTLE OVER THE PACIFIC
NORTHWEST LATE NEXT WEEK WITH SNOW DOWN INTO AT LEAST THE CASCADE
FOOTHILLS AND COAST RANGE.
&&

.SHORT TERM...RAINFALL CONTINUED THROUGHOUT THE FORECAST AREA THIS
EVENING IN A STRONG AND MOIST WESTERLY FLOW. RADAR AND SURFACE
OBSERVATIONS IN RECENT HOURS SUGGEST A SUBTLE SWITCH TO FOCUSING THE
HEAVIEST RAIN OVER THE CASCADES...WHICH SEEMS TO LINE UP WITH MODEL
TRENDS REASONABLY WELL. ADDITIONALLY A COMPACT SHORTWAVE SEEN IN
WATER VAPOR IMAGERY SHOULD MOVE ACROSS WESTERN WA LATE THIS
EVENING...WHICH SHOULD DIMINISH RAINFALL N OF THE COLUMBIA LATER
TONIGHT.

DESPITE LOWER FLOWS ON COASTAL RIVERS THIS MORNING...SOME MINOR
TIDAL OVERFLOW WAS OBSERVED ALONG THE COAST. THE HIGH TIDE DURING
LATE MORNING ON SUNDAY WILL BE OF ABOUT THE SAME MAGNITUDE...AND
WITH MUCH HIGHER FLOWS EXPECTED DUE TO THE ABUNDANT RAINFALL OVER
THE COASTAL RIVER BASINS...CONFIDENCE IS FAIRLY HIGH THAT AT LEAST
SOME MINOR TIDAL OVERFLOW IMPACTS WILL BE OBSERVED ON SUNDAY WITH
TOTAL TIDES PUSHING NEAR 11 FT WITH COASTAL RIVERS APPROACHING OR
EXCEEDING BANKFULL. LOW LYING AREAS NEAR WILLAPA BAY...TILLAMOOK
BAY...DEPOE BAY...WALDPORT...AND FLORENCE...ALONG WITH STRETCHES
OF HIGHWAY 101 ALONG THE COAST...MAY EXPERIENCE MINOR TIDAL
OVERFLOW DURING THE HIGH TIDE AROUND 11 AM SUNDAY. PEAK IMPACTS
ARE LIKELY BETWEEN ABOUT 9 AM AND 3 PM. WITH RIVERS CONTINUING TO
RUN AT OR NEAR FLOOD STAGE...THE MIDDAY HIGH TIDE ON MONDAY MAY
AGAIN CAUSE SOME MINOR ISSUES.

REMAINDER OF SHORT TERM DISCUSSION UNCHANGED...AS WE GET INTO LATER
SUNDAY...THE COLD FRONT THAT IS CURRENTLY SITTING WELL TO OUR NORTH
OFF THE BRITISH COLUMBIA AND NORTHERN WASHINGTON COAST WILL SLOWLY
BEGIN TO WORK IT/S WAY SOUTHWARD INTO OUR CWA. BEHIND THE COLD
FRONT...THE STRONG OROGRAPHIC FLOW WILL WEAKEN AND PRECIPITATION
TAPER OFF CONSIDERABLY. THE CURRENT FCST MODEL TIMING HAS THE PRECIP
OVER S WASHINGTON TAPERING OFF SUN AFTERNOON...AND THE N OREGON
CASCADES AND COAST RANGE DROPPING OFF SUN EVENING. THE HEAVIER
PRECIPITATION BECOMES INCREASINGLY CONFINED TO THE CENTRAL OR
CASCADES AND COAST RANGE TOMORROW. EVENTUALLY THE COLD FRONTS ALL
THE WAY THROUGH THE FCST AREA SUN NIGHT INTO EARLY MON MORNING. SNOW
LEVELS WILL FALL BEHIND THE COLD FRONT...WHICH MAY ALLOW FOR A FEW
INCHES OF SNOWFALL ACCUMULATION DOWN TO NEAR THE CASCADE PASSES LATE
SUNDAY OR EARLY MON BEFORE THE PRECIPITATION COMPLETELY ENDS.

CONDITIONS LOOK DRIER FOR MON AS UPPER LEVEL RIDGING BUILDS OVER THE
PAC NW. THE 12Z ECMWF IS INDICATING THAT THE BAROCLINIC ZONE TO OUR
SOUTH MAY TRY TO LIFT NORTHWARD AGAIN AS A WARM FRONT ON MON...SO DID
NOT COMPLETELY REMOVE POPS. BUT THE NAM AND GFS ARE COMPLETELY
DRY...SO STAYED WITH LOW CHANCE POPS FOR NOW.

MAINLY DRY CONDITIONS WILL LIKELY CONTINUE ON FOR MUCH OF TUE.
HOWEVER...FCST CONFIDENCE IS A LITTLE BETTER THAT WE WILL SEE SOME
LIGHT RAIN ON TUE NIGHT OR WED AS A WEAK FRONTAL SYSTEM TO THE NORTH
MOVES THROUGH THE WEAKENING UPPER LEVEL RIDGE. PYLE

&&

.LONG TERM...NO CHANGES. PREVIOUS DISCUSSION FOLLOWS. TUESDAY NIGHT
THROUGH SATURDAY...MODELS REMAIN CONSISTENT IN FLATTENING AN UPPER
LEVEL RIDGE LATE TUESDAY INTO WEDNESDAY. THERE ARE SOME MODEL
DISCREPANCIES CONCERNING HOW FAR SOUTH THE NEXT SHORTWAVE WILL MOVE
INTO THE PACIFIC NORTHWEST...BUT OVERALL AN UPPER LEVEL TROUGH WILL
SAG SOUTH AND MOVE INLAND EARLY WEDNESDAY. THIS WILL USHER IN
ANOTHER BATCH OF COOL AND RAINY CONDITIONS...WITH SNOW LEVELS
DROPPING TO NEAR 2000 FT SO EXPECT SNOW SHOWERS OVER CASCADE PASSES
RIGHT IN TIME FOR HOLIDAY TRAVEL. AGAIN...HOLIDAY TRAVELERS HEADED
OVER THE CASCADE PASSES WILL CERTAINLY NEED TO MONITOR THE FORECAST.
LINGERING MOISTURE CONTINUES INTO CHRISTMAS DAY...BUT WILL LIKELY BE
OCCASIONAL SHOWERS WITH PARTLY CLOUDY SKIES FOR THE MOST PART.
COLDER NORTHERLY FLOW PERSISTS INTO EARLY NEXT WEEKEND...WITH DRIER
CONDITIONS EXPECTED FOR FRIDAY. A NEW DEVELOPMENT IN THE 12Z MODEL
RUNS HAS BEEN ANOTHER SHORTWAVE DISTURBANCE DROPPING SOUTH OVER THE
FORECAST AREA LATE FRIDAY...BRINGING A THREAT FOR RAIN AND SNOW ON
THE MOUNTAINS.
/27
&&

.HYDROLOGY...NUMEROUS FLOOD WARNINGS ALREADY IN EFFECT...INCLUDING
MAJOR FLOODS FOR THE MARYS AND CLACKAMAS RIVERS. FLOODING ALONG THE
MAINSTEM WILLAMETTE LOOKS UNLIKELY AT THIS POINT.
&&

.AVIATION...FLIGHT CONDITIONS ARE BEGINNING TO IMPROVE IS SPOTS
INLAND AS THE AIR MASS BECOME MORE MIXED. RADAR SHOWS RAIN
CONTINUES TO STREAM INTO THE AREA WITH A SOME RAIN SHADOWING OVER
THE VALLEY. THERE SHOULD BE A VFR WITH MVFR MIXED IN INLAND
THROUGH SUN MORNING WITH PERHAPS LESS MVFR SUN AFTERNOON. COASTAL
AREAS SHOULD BE PRIMARLY LIFR TO IFR THROUGH SUN MORNING WITH
IMPROVEMENT TO MVFR. EXPECT MOUNTAINS TO REMAIN OBSCURED THROUGH
SUN.

KPDX AND APPROACHES...LIKELY TO SEE A MIX OF MVFR AND LOW VFR
THROUGH SUN MORNING WITH A BETTER CHANCE FOR PRIMARLY VFR IN THE
AFTERNOON. /27

&&

.MARINE...WINDS REMAIN GUSTY BUT PRIMARLY IN THE SMALL CRAFT
ADVIOSORY CATEGORY SO HAVE ENDED THE GALES. THE STRONGEST WINDS
WITH BE ALONG THE NORTHERN BORDER TONIGHT SO THERE MAY BE A FEW
GUSTS TO 35 KT. WINDS CONTINUE TO EASE THROUGH DAY SUN...WITH
WINDS GENERALLY 15 KT OR LESS AND BECOMING MORE W AND THEN NW.
WINDS MAY INCREASE AGAIN AROUND MIDWEEK INTO SMALL CRAFT ADVISORY
RANGE AS A FRONTAL SYSTEM APPROACHES.

SEAS ARE SLOWLY SUBSIDING BUT WILL REMAIN AROUND 17 FT TONIGHT
THEN AROUND 15 FT SUN AFTERNOON. AT THIS LEVEL HIGH SURF
CONDITIONS HAVE ENDED. HOWEVER...SEAS LIKELY REMAIN IN THE LOW TO
MID TEENS THROUGH AT LEAST THE FIRST HALF OF THE WEEK AND POSSIBLY
UNTIL FRIDAY. /26

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...FLOOD WATCH 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.

     COASTAL FLOOD ADVISORY FROM 9 AM TO 3 PM PST SUNDAY
     FOR CENTRAL OREGON COAST-NORTH OREGON COAST.

WA...FLOOD WATCH 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.

     COASTAL FLOOD ADVISORY FROM 9 AM TO 3 PM PST SUNDAY FOR SOUTH
     WASHINGTON COAST.

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

     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 4 PM PST
     MONDAY FOR COASTAL WATERS FROM CAPE SHOALWATER WA TO
     FLORENCE OR OUT 60 NM.

     SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR
     UNTIL 10 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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