Area Forecast Discussion
Issued by NWS Portland, OR

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000
FXUS66 KPQR 132201
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
201 PM PST SAT FEB 13 2016

.SYNOPSIS...A STRONG WARM FRONT IS SPREADING RAIN AND BREEZY
CONDITIONS INTO SOUTHWEST WASHINGTON AND NORTHWEST OREGON THIS
AFTERNOON. RAIN WILL BECOME HEAVY AT TIMES...ESPECIALLY ALONG THE
COAST AND IN THE HIGHER TERRAIN. SNOW LEVELS ARE STARTING OFF NEAR
THE CASCADE PASSES...BUT ARE EXPECTED TO RISE TONIGHT AS WARMER AIR
MOVES IN. THE FRONTAL ZONE WILL LINGER OVER THE AREA SUNDAY...THEN
LIFT NORTH SUNDAY NIGHT AND MONDAY FOR DECREASING RAIN. HIGH PRESSURE
WILL BRING DRIER WEATHER LATER MONDAY INTO TUESDAY...ESPECIALLY FOR
SOUTHERN ZONES. AN UPPER LEVEL TROUGH IS EXPECTED TO BRING COOLER AND
SHOWERY WEATHER LATER WEDNESDAY INTO THURSDAY...WITH SNOW POSSIBLE
FOR THE CASCADE PASSES AND ABOVE.

&&

.SHORT TERM...TONIGHT THROUGH TUESDAY...NWS DOPPLER RADAR SHOWS RAIN
SPREADING EASTWARD ACROSS THE FORECAST AREA THIS AFTERNOON...MAINLY
NORTH OF A LINCOLN CITY TO SALEM LINE. THIS IS ASSOCIATED WITH A
POTENT PACIFIC FRONTAL SYSTEM WHICH WILL PUSH A WARM FRONT ACROSS THE
FORECAST AREA TONIGHT. LOOKING AT THE BIGGER PICTURE...THIS FRONTAL
SYSTEM HAS A DECENT MOISTURE TAP ALL THE WAY BACK TO THE SUBTROPICAL
LATITUDES NEAR THE DATELINE. BLENDED PRECIPITABLE WATER VALUES SHOW
1.2 INCH OR HIGHER WITHIN THIS MOISTURE PLUME AS FAR EAST AS 130W.
12Z NAM/GFS SUGGEST PW VALUES AROUND 1 INCH REACHING OUR FORECAST
AREA THIS EVENING...COUPLED WITH OROGRAPHICALLY FAVORABLE W-SW WINDS
OF 40-50 KT AT 850 MB. THIS SHOULD YIELD A PERIOD OF FAIRLY HEAVY
RAINFALL FOR THE COAST AND HIGHER TERRAIN... ESPECIALLY NORTHERN
ZONES WHERE 2-4 INCHES OF RAIN ARE POSSIBLE BY SUNDAY. INLAND VALLEYS
WILL SEE LESS...RANGING FROM AROUND 0.50 INCH SOUTH OF SALEM TO
AROUND 1 INCH IN THE PDX METRO. 12Z GFS SHOWS THE BEST ISENTROPIC
LIFT MOVING THROUGH BY MIDNIGHT TONIGHT. AFTER THAT FORCING MOVES
EAST...THE WILLAMETTE VALLEY WILL LIKELY BE HEAVILY RAIN SHADOWED IN
LOW-LEVEL WESTERLY FLOW LATER TONIGHT INTO SUNDAY.

SNOW AMOUNTS REMAIN A CHALLENGING FORECAST FOR THE CASCADES WITH THIS
SYSTEM. OFTEN TIMES...LEFTOVER COLD AIR...WET-BULB EFFECTS AND LATENT
HEAT PROCESSES WILL HOLD ON TO LOWER SNOW LEVELS MOUNT HOOD NORTHWARD
A BIT LONGER THAN MODELS EXPECT. HOWEVER THIS DOES NOT APPEAR TO BE
ONE OF THOSE SCENARIOS AS FAIRLY STRONG WARM ADVECTION WILL BE MOVING
IN ON THE 40-50 KT W-SW 850-700 MB FLOW LATER TONIGHT. SOME WET SNOW
IS POSSIBLE FOR THE PASSES THIS AFTERNOON INTO THIS EVENING...BUT
ACCUMULATIONS SHOULD BE LIGHT. HIGHER SKI RESORT ELEVATIONS LOOK MORE
LIKELY TO SEE 5-10 INCHES BEFORE SNOW LEVELS SKYROCKET TO 7000 FEET
SUNDAY MORNING. IF SNOW LEVELS REMAIN LOWER THAN EXPECTED...SNOW
ACCUMULATIONS COULD BE SUBSTANTIALLY HIGHER GIVEN THE HEAVY QPF THAT
IS EXPECTED. HOWEVER...AM FAIRLY CONFIDENT THAT THE CHANGEOVER WILL
BE QUICK LATER TONIGHT OR SUNDAY MORNING. NOT EXPECTING TO CHANGE
MUCH WITH THE EXISTING WINTER WX ADVISORY FOR SNOW...THOUGH WILL
PROBABLY ADD SOME WORDING TO SUGGEST THE GREATEST ACCUMULATIONS WILL
LIKELY REMAIN UP IN THE HIGHER SKI RESORT ELEVATIONS.

THE HEAVY RAINFALL MAY CAUSE SOME MINOR HYDROLOGIC ISSUES...MAINLY
FOR CREEKS AND SMALL STREAMS DRAINING OUT OF THE COAST RANGE AND
CASCADES. THE GRAYS RIVER IN WAHKIAKUM COUNTY IS NOTORIOUSLY FAST-
RESPONDING...SO 2-4 INCHES OF RAIN IN A 24 HOUR PERIOD MAY PUSH IT
CLOSE TO BANKFULL. WILL BE KEEPING A CLOSE EYE ON THIS RIVER AMONG
OTHERS AS RAIN INCREASES LATER TODAY AND TONIGHT...BUT SIGNIFICANT
MAIN STEM RIVER FLOODING IS NOT EXPECTED AT THIS TIME.

UPPER LEVEL RIDGING WILL BEGIN BUILDING IN FROM THE SW SUNDAY...BUT
WEAK SHORTWAVES WILL LIKELY RIDE OVER THE TOP OF THE RIDGE AND REMAIN
INTACT TO KEEP SOME RAIN IN THE PICTURE THROUGH SUN EVENING. DRYING
TREND IS EXPECTED MON/TUE AS THE UPPER RIDGE SHOVES THE MAIN
BAROCLINIC ZONE NORTHWARD INTO WA/BC. SW WA MAY REMAIN CLOSE ENOUGH
TO THE FRONTAL ZONE TO KEEP SOME RAIN OR DRIZZLE AROUND...BUT AREAS
PDX METRO SOUTHWARD SHOULD BE MAINLY DRY MON/TUE. STRENGTHENING
INVERSIONS MAY PROMOTE NIGHT AND MORNING FOG... ESPECIALLY SOUTH OF
SALEM WHERE SKIES HAVE THE BEST CHANCE OF CLEARING. ANY FOG THAT DOES
DEVELOP MAY BE STUBBORN. DID NOT FACTOR THIS INTO MON/TUE MAX TEMP
FORECASTS YET...AS THERE REMAINS A GOOD DEAL OF UNCERTAINTY AS TO IF
AND WHERE FOG WILL DEVELOP.  WEAGLE

.LONG TERM...TUESDAY NIGHT THROUGH FRIDAY...THE UPPER RIDGE
RESPONSIBLE FOR THE DRYING TREND MON/TUE WILL SHIFT EAST MIDWEEK...
WITH MODELS SHOWING GOOD CONSENSUS IN BRINGING A WELL DEFINED UPPER
TROUGH INTO THE PAC NW AND POSSIBLY CALIFORNIA WED NIGHT/THU. THIS
WILL CAUSE RAIN CHANCES TO INCREASE LATER WED...WITH COOL AND SHOWERY
WEATHER LINGERING INTO THU. AIR MASS WILL START OUT RATHER WARM WITH
SNOW LEVELS WELL ABOVE THE CASCADE PASSES WED. COLDER AIR WILL MOVE
IN WITH THE UPPER TROUGH...WITH SNOW LEVELS LOWERING TO 3000 TO 3500
FEET IN SHOWERS BY THURSDAY. EXPECT TEMPS TO DROP BACK TO NEAR NORMAL
LATE WEEK AS A RESULT OF THE UPPER TROUGH...POSSIBLY EVEN A LITTLE
BELOW NORMAL. MODELS SHOW DECENT AGREEMENT THAT THIS UPPER TROUGH
WILL BE FOLLOWED BY A MORE PROGRESSIVE FRONTAL SYSTEM FOR MORE RAIN
AND CASCADE SNOW FRI/FRI NIGHT.  WEAGLE

&&

.AVIATION...WARM-FRONTAL PRECIP BEGINNING TO SPREAD INTO THE S
WASHINGTON AND N OREGON COAST EARLY THIS AFTERNOON. VFR ACROSS THE
AREA...EXCEPT AREAS OF MVFR ALONG THE COAST. FLIGHT CONDITIONS
ALONG THE COAST DETERIORATE THROUGH THE AFTERNOON AND EARLY
EVENING...DROPPING TO IFR BY 00Z SUN. MVFR COVERAGE TO INCREASE
OVER THE INTERIOR LOWLANDS AFTER 00Z SUN. INTERIOR VALLEYS MAY
SEE MORE VFR OVERNIGHT THROUGH SUN DUE TO RAIN-SHADOW EFFECTS.
STRONG 850 MB WEST FLOW WILL RESULT IN ENHANCED OROGRAPHIC LIFT
OVER THE HIGHER TERRAIN...RESULTING IN MOUNTAIN OBSCUREMENT AND
IFR OR WORSE FLIGHT CONDITIONS.

KPDX AND APPROACHES...VFR AT 21Z. CIGS WILL CONTINUE TO LOWER
THROUGH THE AFTERNOON AND EARLY EVENING...WITH MVFR CONDITIONS
LIKELY AFTER 02Z SUN...ESPECIALLY ALONG WRN APPROACHES. S WIND
SHOULD ALLOW FOR LONGER-DURATION VFR CONDITIONS OVERNIGHT THROUGH
SUN. WEISHAAR

&&

.MARINE...WIND GUSTS ON THE EDGE OF GALE FORCE OVER THE NRN OUTER
WATERS EARLY THIS AFTERNOON. THE 14Z RUC RUN WAS A LITTLE STRONGER
COMPARED TO THE 12Z NAM. GALE FORCE WIND GUSTS OVER THE OUTER NRN
WATERS THROUGH 06Z SUN. HELD ON TO THEM A LITTLE LONGER OVER THE
NRN INNER WATERS...EXTENDING THE GALE TO 08Z. WILL ALSO NEED TO
WATCH THE NRN PART OF PZZ255 AND PZZ275 AS GUSTS COULD TOUCH GALE
FORCE TONIGHT. MODELS IN DECENT AGREEMENT SHOWING SMALL CRAFT
ADVISORY SPEEDS LATE TONIGHT THROUGH EARLY SUN AFTERNOON. 12Z NAM
BOUNDARY LAYER WIND SPEEDS A LITTLE STRONGER 18Z SUN COMPARED TO
THE GFS. WIND SPEEDS EASE A BIT MON AS THE WARM FRONT LIFTS
N...REDUCING THE SURFACE GRADIENT. BASICALLY WENT WITH THE GFS FOR
WIND MON THROUGH TUE NIGHT. MODEL DIFFERENCES BECOME GREATER WED
THROUGH THU REGARDING THE NEXT SIGNIFICANT WEATHER SYSTEM. THE
ECMWF SEEMS TO BE MORE CONSISTENT...SHOWING POSSIBLE GALES LATE
WED THROUGH EARLY THU MORNING.

A LONG PERIOD NW SWELL WILL MAINTAIN SEAS 12 TO 15 FT THROUGH
TONIGHT AS THE WIND WAVE COMPONENT INCREASES. SEAS WILL SUBSIDE
TO AROUND 10 FT SUN AFTERNOON. LATEST ENP RUN HAS SEAS INCREASING
TO NEAR 15 FT LATE NEXT WEEK AND POSSIBLY NEAR 20 FT NEXT WEEKEND.
WANT TO SEE A FEW MORE RUNS BEFORE GOING THAT HIGH. CAPPED SEAS TO
AROUND 15 FT FOR NOW. WEISHAAR

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...WINTER WEATHER ADVISORY UNTIL 10 PM PST THIS EVENING FOR
     NORTHERN OREGON CASCADES.

WA...WINTER WEATHER ADVISORY UNTIL 4 AM PST SUNDAY FOR SOUTH
     WASHINGTON CASCADES.

PZ...GALE WARNING UNTIL 10 PM PST THIS EVENING FOR WATERS FROM CAPE
     SHOALWATER WA TO CASCADE HEAD OR FROM 10 TO 60 NM.

     SMALL CRAFT ADVISORY FOR WINDS UNTIL 6 PM PST SUNDAY FOR
     COASTAL WATERS FROM CASCADE HEAD OR TO FLORENCE OR OUT 60 NM.

     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 4 PM PST SUNDAY
     FOR COASTAL WATERS FROM CASCADE HEAD OR TO FLORENCE OR OUT 60
     NM.

     SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR UNTIL 10 AM
     PST SUNDAY.

     GALE WARNING UNTIL MIDNIGHT PST TONIGHT FOR COASTAL WATERS FROM
     CAPE SHOALWATER WA TO CASCADE HEAD OR OUT 10 NM.

&&

$$

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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