Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 182130
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
224 PM PDT FRI APR 18 2014

.SYNOPSIS...HIGH PRESSURE TODAY GIVES WAY TO THE NEXT FRONTAL SYSTEM
THAT WILL MOVE THROUGH THE REGION ON SATURDAY FOR MORE RAIN. WEAK
HIGH PRESSURE RETURNS SATURDAY NIGHT...AND THEN STRENGTHENS SUNDAY.
WARMER SOUTHWEST FLOW ALOFT SUNDAY WILL ALLOW INLAND DAYTIME
TEMPERATURES TO BE A FEW DEGREES ABOVE NORMAL. THE DRY PERIOD IS
EXPECTED TO HOLD THROUGH SUNDAY NIGHT...POSSIBLY AS LONG AS MONDAY
MORNING...AS THE MAIN COLD FRONT STALLS OFF THE COAST. THE FRONT
FINALLY MOVES ONSHORE MONDAY AFTERNOON INTO TUESDAY. THE PATTERN WILL
THEN REMAIN FAIRLY UNSETTLED THROUGH MUCH OF THE WEEK WITH COOLER
CONDITIONS AND PERIODS OF SHOWERS.
&&


&&

.SHORT TERM...TONIGHT THROUGH MONDAY...
SURFACE HIGH PRESSURE REMAINS IN CONTROL FOR A GENERALLY PLEASANT AND
CALM AFTERNOON. HIGH CLOUDS ARE ALREADY MOVING OUT AHEAD OF AN
OCCLUDING FRONTAL SYSTEM IN THE NE PACIFIC. THE CENTER OF THE UPPER
CIRCULATION IS ENCROACHING ON 140W WITH A NICE COMMA CLOUD PATTERN.

MODELS REMAIN IN GOOD AGREEMENT THAT THE COLD FRONT ASSOCIATED WITH
THIS UPPER LOW WILL REACH THE COAST IN THE MORNING AND THE INTERIOR
IN THE AFTERNOON. THIS FRONT WILL SPREAD RAIN THROUGH THE PACIFIC NW
ON SATURDAY...BEGINNING AROUND DAYBREAK SATURDAY...AND LIKELY
REACHING MOST OF THE INTERIOR VALLEYS BEFORE THE MORNING IS OVER.
STEADIEST RAIN IS LATE MORNING THROUGH EARLY AFTERNOON WITH THE FRONT
AS THE UPPER TROUGH AXIS SLIDES ALONG THE WA/OR BORDER. EXPECT BREEZY
CONDITIONS AT THE COAST AND TO SOME DEGREE FOR THE INTERIOR ALONG AND
AHEAD OF THE COLD FRONT. WHILE THIS SYSTEM DOES NOT HAVE LARGE
IMPACTS ON THE INTERIOR...IT WILL BE SENDING LARGE WAVES WITH LONG
PERIODS THAT WILL CREATE HAZARDOUS CONDITIONS IN THE SURF ZONE ON
SATURDAY EVENING AND SATURDAY NIGHT...AND A HIGH SURF ADVISORY IS IN
EFFECT FOR THE S WA AND N OR COASTS.

ONCE AGAIN SNOW LEVELS START HIGH AND THE DIP TO NEAR THE PASSES
BEHIND THE FRONT AS PRECIPITATION BEGINS TO WANE...BUT SOME SHOWERS
WILL LINGER IN THE CASCADES IN THE EVENING FOR SOME LIGHT SNOW
SHOWERS CLOSE TO THE PASSES....ESPECIALLY NORTH OF THE NEWPORT TO MT
JEFFERSON LINE. SURFACE HIGH PRESSURE BUILDS IN RESPONSE TO
SUBSIDENCE BEHIND THE FRONT AND WE REMAIN IN ZONAL FLOW TO SOMEWHAT
WEAK RIDING SATURDAY NIGHT. MAYBE ENOUGH CLEARING FOR SOME PATCHY FOG
INTO SUNDAY MORNING

ON SUNDAY UPPER LEVEL RIDGING BUILDS OVER THE INTERIOR NORTHWEST AND
INTO THE NORTHERN ROCKIES AS THE MASSIVE UPPER TROUGH IN THE GULF OF
ALASKA AMPLIFIES. ADDITIONAL SHORTWAVE ENERGY MOVES THROUGH THE BASE
OF THIS TROUGH AND KICKS A COLD FRONT AND ITS ASSOCIATED MOISTURE
FEED TOWARD THE COAST...BUT IT GETS HUNG UP OFFSHORE DUE TO THE
AMPLIFIED FLOW AND HIGH PRESSURE INLAND. THEREFORE MOST OF SUNDAY IS
LOOKING DRY AND FAIRLY NICE AND POTENTIALLY THE WARMEST DAY OF THE
UPCOMING WEEK.850MB TEMPS WARM TO AROUND 5C IN THE FAR
N TO NEAR 10C IN THE FAR S. THIS TRANSLATES TO MAX TEMPS A FEW
DEGREES ABOVE NORMAL WHICH SUPPORTS MID 60S...EVEN WARMER
SOUTH...DESPITE A VEIL OF HIGH CLOUD COVER STREAMING IN AHEAD OF THE
OFFSHORE TROUGH. /KMD

.LONG TERM...MONDAY NIGHT THROUGH THURSDAY...FLOW CONTINUES TO
AMPLIFY SUNDAY NIGHT AND THIS WILL ORIENT THE COLD FRONT OFFSHORE
MORE NORTH TO SOUTH...THUS ANY PRECIPITATION WILL REMAIN WELL
OFFSHORE SUNDAY NIGHT. THE COLD FRONT FINALLY GETS A SHOVE AS THE
UPPER JET NOSES INTO THE AREA. PRECIPITATION IS MAINLY TIED TO THE
FRONT...BUT WITH THE MARGINALLY UNSTABLE SW FLOW...MODELS SHOW THAT
THERE COULD BE SOME SHOWERS IN THE AFTERNOON MAINLY FOR THE
CASCADES...AS MID LEVEL LAPSE RATES HOVER IN THE 6 TO 7 DEG/KM RANGE.
INSTABILITY PARAMETERS ARE NOT THAT IMPRESSIVE...SO THUNDER POTENTIAL
LOOKS LOW AT THIS TIME.

LOOKS LIKE TUE AND WED WILL BE CHARACTERIZED BY COOL AND DAMP
CONDITIONS AS THE DEEP UPPER LOW MIGRATES ACROSS THE PAC NW AND INTO
THE NRN ROCKIES. AFTER THE FIRST LARGE UPPER TROUGH CLEARS LATE
TUESDAY NIGHT AND MAYBE A BREAK IN SHOWERS WEDNESDAY...ANOTHER DEEP
UPPER LOW WILL SPREAD SEVERAL WAVES OF SHOWER ACTIVITY THROUGH THE
AREA FOR THE LATTER HALF OF THE WEEK.. /KMD
&&

.AVIATION...VFR PREVAILING THROUGH MOST OF TONIGHT. A COLD FRONT
IS FORECAST TO REACH THE COAST AROUND MID MORNING SAT...AND TO THE
INTERIOR VALLEYS AROUND MIDDAY. EXPECT MVFR CIGS AROUND 12Z-15Z
SAT AT THE COAST AND 18Z-20Z SAT AT INLAND TAF SITES. CONDITIONS
TRENDING TOWARD VFR LATER SAT AFTERNOON.

KPDX AND APPROACHES...VFR EXPECTED THROUGH EARLY SAT MORNING THEN
MVFR CIGS BECOMING LIKELY BY 18Z SAT AS A COLD FRONT APPROACHES
THE AREA.

&&

.MARINE...A RELATIVELY QUIET PERIOD THIS EVENING WITH WEAK HIGH
OVER THE WATERS. THE HIGH PRES GIVES WAY TO A FRONT LATER TONIGHT
WHICH SHOULD BRING SMALL CRAFT ADVISORY WINDS OVER ALL WATERS
LATER TONIGHT AND SAT. COULD SEE SOME GUSTS 30-35 KT AS THE FRONT
MOVES THROUGH...MOVING ASHORE AROUND SUNRISE SAT. WINDS THEN
DIMINISH FROM SOUTH TO NORTH SAT AFTERNOON AND NIGHT.

A LARGE SWELL TRAIN WILL FOLLOW THE FRONT SAT EVENING INTO SUN.
SEAS APPEAR ON TRACK TO RAPIDLY BUILD TO 17 TO 20 FT AT 16 SECONDS
AROUND 11 PM SAT NIGHT...PEAKING BETWEEN MIDNIGHT AND 5 AM SUN.
SEAS WILL SLOWLY SUBSIDE SUN MORNING BUT REMAIN IN THE 13 TO 16 FT
RANGE THROUGH SUN NIGHT...AND TO 10 FT LATE MON. A SMALL CRAFT
ADVISORY FOR SEAS HAS BEEN ISSUED FOR THIS SWELL TRAIN.

A HIGH SURF ADVISORY CONTINUES FOR LATER SAT NIGHT THROUGH SUN
MORNING FOR THE SOUTH WASHINGTON AND NORTH OREGON COASTS. THE
CENTRAL COAST WILL PROBABLY REMAIN JUST UNDER ADVISORY CRITERIA.

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...HIGH SURF ADVISORY FROM 10 PM SATURDAY TO 10 AM PDT SUNDAY FOR
     NORTH OREGON COAST.

WA...HIGH SURF ADVISORY FROM 10 PM SATURDAY TO 10 AM PDT SUNDAY FOR
     SOUTH WASHINGTON COAST.

PZ...SMALL CRAFT ADVISORY FOR WINDS FROM 2 AM TO 9 PM PDT SATURDAY
     FOR COASTAL WATERS FROM CAPE SHOALWATER WA TO CASCADE HEAD OR
     OUT 60 NM.

     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS FROM 4 PM SATURDAY TO 6
     AM PDT MONDAY FOR COASTAL WATERS FROM CAPE SHOALWATER WA TO
     FLORENCE OR OUT 60 NM.

     SMALL CRAFT ADVISORY FOR WINDS FROM 2 AM TO 4 PM PDT SATURDAY
     FOR COASTAL WATERS FROM CASCADE HEAD OR TO FLORENCE OR OUT 60
     NM.

&&

$$

MORE WEATHER INFORMATION ONLINE AT...
    HTTP://WEATHER.GOV/PORTLAND

INTERACT WITH US VIA SOCIAL MEDIA
    WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.PORTLAND.GOV
    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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