Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 212311
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
310 PM PST SUN DEC 21 2014

.SYNOPSIS...THE REMNANTS OF AN ATMOSPHERIC RIVER CONTINUE TO BRING
MODERATE RAIN AT TIMES OVER THE HIGHER TERRAIN OF THE OREGON CASCADES
AND COAST RANGE. PRECIPITATION WILL TAPER OFF TONIGHT INTO EARLY MON
AS THE BAROCLINIC ZONE STALLS AND WEAKENS OVER SOUTH-CENTRAL OREGON.
THE HEAVY RAINFALL OVER THE WEEKEND CAUSED NUMEROUS RIVERS TO REACH
FLOOD STAGE. RIVER FLOODING IMPACTS WILL CONTINUE TONIGHT AND INTO
EARLY NEXT WEEK. THE STALLED BAROCLINIC ZONE OVER CENTRAL OREGON WILL
LIFT NORTH AS A WEAK WARM FRONT LATER MON AND MON NIGHT. THEN A
STRONGER FRONTAL SYSTEM WILL BRING A QUICK SHOT OF PRECIPITATION TUE
NIGHT INTO WED. THIS SYSTEM WILL USHER IN A COLDER AIR MASS AND BRING
POTENTIAL FOR SOME ACCUMULATING SNOW TO THE CASCADE PASSES LATER WED
INTO THU.  A QUIET WEATHER PERIOD APPEARS TO BE IN STORE LATE NEXT
WEEK AS UPPER LEVEL RIDGING BUILDS OVER THE PAC NW. ANOTHER SYSTEM
MAY BRING BRING PRECIPITATION AT SOME POINT OVER THE WEEKEND.

&&

.SHORT TERM...TONIGHT THROUGH WEDNESDAY...
THE HEAVY RAINFALL OVER THE WEEKEND CAUSED NUMEROUS RIVERS TO REACH
FLOOD STAGE. RIVER FLOODING IMPACTS WILL CONTINUE TONIGHT AND INTO
EARLY NEXT WEEK. SEE THE HYDROLOGY SECTION BELOW FOR MORE DETAILS.

THE REMNANTS OF THE ATMOSPHERIC RIVER CONTINUE TO BRING MODERATE RAIN
AT TIMES OVER THE HIGHER TERRAIN OF THE OREGON CASCADES AND COAST
RANGE THIS AFTERNOON. HOWEVER THE HEAVIEST PRECIP HAS LONG SINCE
ENDED...AS THE OROGRAPHIC FORCING HAS WEAKENED AND AVAILABLE MOISTURE
HAS BEGUN TO DECREASE. BUT BATCHES OF ENHANCED MOISTURE HAVE BEEN
MOVING ONSHORE AND ENHANCING THE PRECIP PERIODICALLY TODAY. THE
RAINFALL WILL TAPER OFF EVEN MORE TONIGHT INTO EARLY MON MORNING AS
UPPER LEVEL RIDGING BEGINS TO BUILD OVER THE PAC NW AND FURTHER CUTS
OFF THE SUB-TROPICAL MOISTURE TAP THAT HAS BEEN FEEDING INTO THIS
SYSTEM. A COLD FRONT IS SLOWLY PUSHING IN FROM THE NORTH TODAY...AND
WILL CONTINUE TO MOVE SLOWLY SOUTH TONIGHT...EVENTUALLY STALLING AND
WEAKENING OVER SOUTH-CENTRAL OREGON EARLY MONDAY. MORE ORGANIZED
PRECIPITATION MAY LINGER INTO MON MORNING OVER THE LANE COUNTY
CASCADES DEPENDING ON HOW FAR SOUTH THE BAROCLINIC ZONE STALLS.
COOLER AIR WILL BE FILTERING IN FROM THE NORTH TONIGHT BEHIND THE
COLD FRONT...WHICH SHOULD ALLOW SNOW LEVELS TO FALL BACK DOWN TO NEAR
THE CASCADE PASSES OVERNIGHT. THERE IS THE POTENTIAL FOR A FEW INCHES
OF SNOWFALL AT SOME OF THE HIGHER NORTH OREGON PASSES THROUGH EARLY
MON...BUT DO NOT EXPECT WE WILL BE NEAR ADVISORY ACCUMULATIONS.

AGREEMENT AMONGST THE FCST MODELS IS INCREASING THAT THERE WILL BE
ANOTHER PERIOD OF LIGHT PRECIP LATE MON INTO TUE...AS A SHORTWAVE
TROUGH OFFSHORE REACTIVATES THE STALLED BAROCLINIC ZONE AND LIFTS IT
NORTHWARD THROUGH THE REGION AGAIN AS A WEAK WARM FRONT. INCREASED
FCST POPS DURING THIS TIME PERIOD...BUT QPF APPEARS TO FAIRLY
LIMITED. ANOTHER SHORTWAVE IS MODELED TO PUSH THE BOUNDARY THROUGH AS
A FAIRLY SHARP COLD FRONT ON WED. IT APPEARS THAT THERE WILL BE A
BURST OF FAIRLY HEAVY PRECIPITATION WITH THIS SYSTEM...ALONG WITH
DROPPING SNOW LEVELS. THE TIMING IS SOMEWHAT UNCERTAIN AT THIS TIME.
THE 12Z ECMWF MODEL BRINGS PRECIP ONTO THE COAST BEGINNING TUE
AFTERNOON AND SPREADS INLAND OVERNIGHT INTO WED MORNING. THE 12Z GFS
AND NAM ARE ABOUT 6 HRS SLOWER...BRINGING MOST OF THE PRECIP THROUGH
DURING THE DAY WED. THIS SYSTEM SHOULD BRING DECENT ACCUMULATING
SNOWFALL TO THE CASCADES DOWN TO THE PASSES. PYLE

&&

.LONG TERM...WED NIGHT THROUGH SUNDAY...
EXPECT LINGERING SHOWERS WED NIGHT AND THU BEHIND THE DEPARTING
FRONTAL PASSAGE EARLIER WED. EXPECT ADDITIONAL LIGHT SNOWFALL
ACCUMULATIONS IN THE CASCADES DURING THIS TIME. THE SNOW LEVEL SHOULD
BE BELOW THE PASSES...POSSIBLY EVEN INTO THE CASCADE FOOTHILLS. GOING
INTO THU NIGHT AND FRI...THERE ARE SLIGHT DIFFERENCES BETWEEN GFS AND
ECMWF MODELS. THE GFS DEVELOPS RIDGING OVER THE PAC NW AND KEEPS US
DRY THROUGH THE REST OF THE WEEK. THE ECMWF HAS A WEAKER RIDGE AND
KEEPS IT FURTHER OFFSHORE...ALLOWING LIGHT SHOWERS TO REMAIN OVER THE
REGION INTO FRI. FCST UNCERTAINTY INCREASES FURTHER NEXT WEEKEND. THE
GFS IS DROPPING A LOW PRES SYSTEM INTO THE INTERIOR PAC NW AND BRINGS
A COLDER AIR MASS. MEANWHILE THE EWMCW IS CLOSING THE LOW OFF AND
KEEPING IT OFFSHORE...WHICH WOULD RESULT IN A WETTER AND MILDER
WEEKEND. WILL AVOID ADDING TO MUCH DETAIL TO THE FCST DURING THIS
TIME PERIOD...AND KEEP A CHC OF POPS THROUGH THE WEEKEND. PYLE

&&

.HYDROLOGY...MODERATE RAIN CONTINUES AT TIMES THIS AFTERNOON. THE
RAIN WILL TAPER OFF TONIGHT INTO EARLY MON. NUMEROUS FLOOD WARNINGS
ARE ALREADY IN EFFECT...BUT ALL LOCAL RIVERS ARE EXPECTED TO REMAIN
BELOW MAJOR FLOOD STAGE. COASTAL RIVERS HAVE CRESTED AND MOST WILL
FALL BELOW FLOOD STAGE THIS AFTERNOON AND EVENING. WILLAMETTE
TRIBUTARIES WILL CONTINUE TO RISE AND ANY FLOODING WILL GENERALLY
BEGIN LATER TODAY. FLOODING ALONG THE MAINSTEM WILLAMETTE LOOKS
UNLIKELY AT THIS POINT. SEE THE LATEST WARNINGS AND FLOOD STATEMENTS
AT WWW.WEATHER.GOV/PORTLAND (LOWER CASE) FOR ADDITIONAL DETAILS.
BOWEN

SOME MINOR TIDAL OVERFLOW WAS AGAIN OBSERVED THIS AFTERNOON AS A HIGH
ASTRONOMICAL TIDE COMBINED WITH HIGHER FLOWS ON THE COASTAL
RIVERS. LOW LYING COASTAL AREAS NEAR WILLAPABAY...ASTORIA...TILLAMOOK
BAY...DEPOE BAY...WALDPORT...AND FLORENCE...ALONG WITH COASTAL
STRETCHES OF HIGHWAY 101 NEAR THE COAST WILL LIKELY SEE SOME MINOR
ISSUES AGAIN. WITH SIMILAR TIDAL VALUES TOMORROW AFTERNOON...IT IS
EXPECTED THAT AT LEAST SOME OF THESE LOCATIONS WILL AGAIN SEE SOME
MINOR OVERFLOW ISSUES. CULLEN

&&

.AVIATION...MODERATE ONSHORE FLOW CONTINUES TODAY WITH ABUNDANT
MID AND HIGH CLOUDS AND SOME RAIN SHOWERS REMAINING. VFR FLIGHT
CONDITIONS FOR MOST LOCATIONS WITH SOME POCKETS OF LOCAL
MVFR...PARTICULARLY ALONG THE COAST AND IN THE SOUTH WILLAMETTE
VALLEY. RAIN GENERALLY CONTINUES TO DECREASE WITH SOME LOWERING
CIGS TONIGHT...TRENDING TOWARDS INCREASING AREAS OF MVFR WITH
LOCAL AREAS OF IFR POSSIBLE OVERNIGHT.

KPDX AND APPROACHES...MOSTLY VFR THROUGH HIS EVENING WITH A FEW
LINGERING SHOWERS POSSIBLE. EXPECT CIGS TO LOWER A BIT OVERNIGHT
WITH MVFR CONDITIONS POSSIBLE AFT 06Z. CULLEN

&&

.MARINE...W-SW WINDS OVER THE WATERS REMAIN AROUND 15 TO 20 KT
THIS AFTERNOON. WINDS WILL CONTINUE TO EASE AND REMAIN LIGHT AND
BECOME MORE W-NW OVERNIGHT THROUGH MON. MEANWHILE...SEAS CONTINUE
TO RUN BETWEEN 13 FT AND 15 FT AND WILL CONTINUE TO SLOWLY SUBSIDE
BUT REMAIN AROUND 11 FT OR 12 FT THROUGH MUCH OF THE WEEK. AN
APPROACHING FRONTAL SYSTEM WILL TURN WINDS SOUTHERLY AGAIN LATE
MON OR EARLY TUE WITH THE POTENTIAL FOR SMALL CRAFT ADVISORY LEVEL
WINDS TUE AND WED AND INCREASE SEAS BACK TO AROUND 15 FT. SEAS
LIKELY FINALLY DROP BELOW 10 FT BY LATER THU OR EARLY FRI. CULLEN

&&

.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 OREGON COAST-CENTRAL WILLAMETTE
     VALLEY-COAST RANGE OF NORTHWEST OREGON-GREATER PORTLAND
     METRO AREA-NORTH OREGON COAST-NORTHERN OREGON CASCADE
     FOOTHILLS-NORTHERN OREGON CASCADES-SOUTH WILLAMETTE VALLEY.

     COASTAL FLOOD ADVISORY UNTIL 3 PM PST THIS AFTERNOON FOR
    CENTRAL OREGON COAST-NORTH OREGON COAST.

     COASTAL FLOOD ADVISORY FROM 10 AM TO 4 PM PST MONDAY FOR
    CENTRAL OREGON COAST-NORTH OREGON COAST.

WA...COASTAL FLOOD ADVISORY UNTIL 3 PM PST THIS AFTERNOON FOR SOUTH
     WASHINGTON COAST.

     COASTAL FLOOD ADVISORY FROM 10 AM TO 4 PM PST MONDAY FOR SOUTH
     WASHINGTON COAST.

PZ...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 6 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 3 PM
    PST MONDAY.

&&

$$

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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