Area Forecast Discussion
Issued by NWS Portland, OR

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000
FXUS66 KPQR 250357
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
856 PM PDT FRI OCT 24 2014

.SYNOPSIS...A DEEPENING LOW PRESSURE AREA WELL OFF THE NORTHERN
CALIFORNIA WATERS THIS AFTERNOON WILL MOVE NORTH TO NORTHEAST TONIGHT
AND SATURDAY. EXPECT A BRIEF PERIOD OF STRONG WIND BEHIND THE LOW
PRESSURE AREA LATE SATURDAY AFTERNOON THROUGH MID-EVENING
...PRIMARILY ALONG THE CENTRAL OREGON COAST AND IN THE INTERIOR
VALLEYS. AN UPPER LEVEL TROUGH OVER THE REGION SUNDAY WILL CONTINUE
SHOWER ACTIVITY. THERE WILL BE A SHORT DRYING PERIOD MONDAY...
FOLLOWED BY ANOTHER SYSTEM TUESDAY. THE TUESDAY SYSTEM COULD BRING
ANOTHER ROUND OF SIGNIFICANT RAINFALL TO THE FORECAST AREA.

&&

.SHORT TERM...A WARM FRONT IS QUICKLY LIFTING NORTHWARD THIS EVENING
AND THE MAIN RAIN BAND IS NOW MOSTLY NORTH OF THE COLUMBIA RIVER. I
SAY MOSTLY...BECAUSE THE FRONT IS BEGINNING TO TILT FROM SW TO NE AS
THE SURFACE COLD FRONT APPROACHES FROM THE SW...CAUSING THE RAIN TO
PERSIST OVER THE NORTH COAST...NORTH OF CANNON BEACH. THE WARM FRONT
SHOULD BE COMPLETELY NORTH OF THE PORTLAND FORECAST AREA AROUND
MIDNIGHT TONIGHT...BUT RAIN FROM THE COLD FRONT WILL ALREADY BE
PUSHING ONSHORE.

SATELLITE IMAGERY SHOWS THE UPPER TROUGH OFFSHORE STRECHING VERTICALLY
SUGGESTING THAT THE TROUGH MAY SPLIT AS THE PREVIOUS NAM MODELS WERE
SHOWING. THERE WAS FAIR UNCERTAINTY WITH THE WINDS OF THIS FORECAST
BEFORE AS THE NAM WAS THE OUTLIER...BUT NOW IT APPEARS THAT THE NAM
MAY BE  THE GFS AND ECMWF. HAVE UPDATED THE WINDS TO
TREND TOWARDS THE 00Z NAM WHICH HAS INCREASED THE WINDS A TAD FROM
THE PREVIOUS FORECAST.

THE WINDS ALONG THE COAST WILL FLIRTING WITH WARNING CRITERIA
SATURDAY AFTERNOON...AND THE VALLEY WINDS WILL BE NEAR ADVISORY
CRITERIA. WOULD LIKE TO SEE THE 00Z GFS BEFORE ISSUING ANY HEADLINES
NOW...SINCE THERE IS SUCH A LARGE DISCREPANCY IN THE POSITION OF THE
SURFACE LOW BETWEEN THE 00 NAM AND THE 18Z GFS. IF THE GFS COMES MORE
IN LINE WITH THE NAM THAN FORECAST CONFIDENCE WILL STRENGTHEN...AND
THERE MAY BE THE NEED FOR SOME WIND PRODUCTS WITH THE MORNING
FORECAST PACKAGE.

BACK TO RAIN...THE RAIN WITH A COLD FRONT WILL MOVE ONSHORE AROUND
MIDNIGHT TONIGHT. DEPENDING ON HOW THE TROUGH SPLITS THERE MAY BE
SOME AREAS ALONG THE COAST THAT WILL BE SLOWER TO SEE THE RAIN THAN
OTHERS. LEANED TOWARDS THE NAM WHICH SHOWS THE CENTRAL OREGON COAST
SEEING THE RAIN FIRST. RAIN SHOULD BE OVER THE ENTIRE FORECAST AREA
BY SATURDAY AFTERNOON. THE FRONT WILL MOVE OVER THE CASCADES SATURDAY
EVENING WITH ABUNDANT SHOWERS FILLING IN BEHIND IT...OVER THE COAST
TO THE WILLAMETTE VALLEY. GENERALLY EXPECT AROUND AN INCH OF RAIN
ALONG THE COAST...COAST RANGE AND THE SW WASHINGTON CASCADES FROM
SATURDAY MORNING THROUGH SATURDAY EVENING...WITH AROUND 0.4 INCH FOR
THE WILLAMETTE VALLEY AND AROUND 0.6 INCH FOR THE OREGON CASCADES AND
CASCADE FOOTHILLS.

AN UPPER TROUGH WILL SWING THROUGH BEHIND THE FRONT AND MAINTAIN
SHOWERS...AS SNOW LEVELS LOWER TO JUST ABOVE THE CASCADE PASSES.
THIS TROUGH IS FAIRLY COOL WITH MODELED UPPER LEVEL TEMPERATURES
AROUND -25C. MODELED LAPSE RATES AROUND 7C/KM...AND NEGATIVE LIS
INDICATE THAT THUNDERSTORMS MAY DEVELOP SUNDAY AFTERNOON. NAM SHOWS
THE MAIN INSTABILITY NEAR THE COAST BUT WESTERLY FLOW MAY CARRY ANY
STORMS THAT FORM WESTWARD. HAVE ADDED A SLIGHT CHANCE OF
THUNDERSTORMS FOR ALL AREAS WEST OF THE CASCADES SUNDAY AFTERNOON AND
EVENING. EXPECT LOCAL 2 TO 4 INCHES OF SNOW ABOVE 4500 FEET.

THE TROUGH PUSHES EAST SUNDAY NIGHT AND THERE MAY BE A BRIEF BREAK IN
RAIN MONDAY BEFORE THE NEXT MOIST FRONT ARRIVES MONDAY NIGHT. TJ

.LONG TERM...THE LONG TERM STARTS OUT WET WITH THE NEXT SYSTEM MOVING
INTO THE FORECAST AREA MON NIGHT. THIS SYSTEM CONTAINS THE REMNANTS
OF HURRICANE ANA...THAT SKIRTED HAWAII LAST WEEK. MODELS MAY BE
UNDER DOING THE  POTENTIAL WITH THIS ONE. A STRONG JET
STREAM WILL REMAIN DIRECTED AT WA AND NRN OREGON THROUGH TUE NIGHT.
MODELS SHOW LARGE VARIATIONS BEGINNING WED...BUT EXPECT THE ACTIVE
PATTERN TO CONTINUE. THE ECMWF AND GFS SHOW A TREND TOWARD DRIER
CONDITIONS LATE NEXT WEEK AS A DEEP LOW IN THE GULF OF ALASKA
AMPLIFIES THE DOWNSTREAM RIDGE OVER THE INTERMOUNTAIN WEST. WEISHAAR

&&

.AVIATION...RAIN HAS MOVED NORTH FASTER THAN MODEL SOLUTIONS HAVE
SHOWN FOR THIS EVENING...WITH SOME LINGERING SHOWERS WITH THE WARM
FRONT OVER THE SW WASHINGTON AND FAR NW OREGON COAST. EXPECT
MOSTLY VFR CONDITIONS TO PREVAIL TONIGHT BEFORE THE ASSOCIATED
COLD FRONT APPROACHES THE REGION MIDDAY SAT. IFR/LIFR FOG OR LOW
STRATUS WILL IMPACT THE CENTRAL AND SOUTHERN WILLAMETTE VALLEY
THROUGH AT LEAST 06-08Z SAT...AND LOCALLY IN THE NORTH WILLAMETTE
VALLEY. RAIN RETURNS TO THE COAST BETWEEN 12-14Z SAT...AND INLAND
BETWEEN 14-16Z SAT. GUSTY SOUTH WINDS WILL ALSO IMPACT THE AREA
AFTER 14Z SAT...STRONGEST GUSTS IN THE AFTERNOON AND EVENING.

KPDX AND APPROACHES...VFR NEXT 24 HRS...EXCEPT FOR A CHANCE FOR
BRIEF MVFR FOG OR LOW STRATUS FROM 08-12Z SAT. RAIN AND GUSTY
SOUTH WINDS WITH GUSTS 25-30 KT POSSIBLE ARE EXPECTED AFTER 14-16Z
SAT...WITH STRONGEST WIND GUSTS IN THE AFTERNOON AND EVENING. /27

&&

.MARINE...A DEEPENING LOW PRES SYSTEM WILL APPROACH FROM THE SW
LATE TONIGHT AND MOVE THROUGH THE COASTAL WATERS ON SAT BEFORE
MOVING INLAND LATE SAT NIGHT. STRONG GALE FORCE WINDS ARE
EXPECTED TO START LATE TONIGHT IN THE CENTRAL OR WATERS AND LAST
THROUGH SAT EVENING. IN THE NORTHERN OR AND SOUTHER WA
WATERS...EXPECT GALE CONDITIONS TO BEGIN EARLY SAT MORNING AND
CONTINUE THROUGH SAT NIGHT. STEEP SEAS ARE EXPECTED WITH THE GALES
WITH WAVE HEIGHTS PEAKING AT AROUND 15 FT SAT EVENING.

AS THE LOW MOVES INLAND...WINDS WILL BECOME W AND DECREASE WITH
SEAS LOWERING TO AROUND 7 TO 9 FT AS HIGH PRES BUILDS INTO THE PAC
NW. ANOTHER SHORTWAVE EXPECTED TO APPROACH THE REGION EARLY NEXT
WEEK WITH SEAS OF 10 TO 12 FT POSSIBLE. /64

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
PZ...GALE WARNING FROM 2 AM TO 11 PM PDT SATURDAY FOR COASTAL
     WATERS FROM CAPE SHOALWATER WA TO CASCADE HEAD OR OUT 60 NM.

     GALE WARNING UNTIL 5 PM PDT SATURDAY FOR COASTAL WATERS FROM
     CASCADE HEAD OR TO FLORENCE OR OUT 60 NM.

     SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR FROM 3 AM
     SATURDAY TO 5 AM PDT 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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