Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 181003
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
248 AM PDT THU SEP 18 2014

.SYNOPSIS...LOW PRES OFF THE N CALIF COAST WILL SLOWLY WEAKEN IS IT
MOVES INTO N CALIF THROUGH THIS EVENING. SOUTHERLY FLOW OVER THE
REGION WILL MAINTAIN CLOUDS AND SCATTERED SHOWERS. DRIER WEATHER FOR
FRIDAY AS HIGH PRES BUILDS...WITH MUCH WARMER AND DRIER CONDITIONS
THIS WEEKEND. COOLER UNSETTLED WEATHER RETURNS NEXT WEEK.
&&

.SHORT TERM...AN UPPER AND SURFACE TROUGH SAGGING OFF THE WEST COAST
IS SLOWLY MOVING EAST OVERNIGHT. A VERTICALLY STACKED LOW WITHIN THE
TROUGH LAY OFF THE NORTHERN CA COAST. MOIST SOUTHERLY FLOW
ESTABLISHED A MILD AIR MASS OVER THE FORECAST AREA. DEWPOINTS ARE IN
THE MID TO UPPER 50S WITH 2 AM TEMPS IN THE UPPER 50S TO LOW 60S WITH
PROBABLY ONLY A FEW MORE DEGREES OF COOLING FOR THIS MORNING. SHOWERS
HAVE BEEN GENERALLY LIGHT AND SCARCE. THE SOUTH WA COAST AND NORTH
OREGON COAST RECEIVED AROUND 0.10 INCH OVER THE PAST SIX HOURS. THIS
APPEARS TO BE ASSOCIATED WITH A DEFORMATION ZONE FROM A WEAK LOW OFF
THE CENTRAL OREGON COAST. THIS AREA CONTINUES TO SHIFT NORTH SO PCPN
SHOULD TAPER OFF SOON. THE LOW OFF THE NORTHERN CA COAST IS KICKING A
SHORTWAVE TO THE NORTHEAST...RADAR SHOWING A SOMEWHAT ORGANIZED BAND
OF SHOWERS OVER SW OREGON. THIS MAY AFFECT LANE COUNTY FOR THE
MORNING COMMUTE...BUT AMOUNTS SHOULD BE LIGHT. OVERALL THE THREAT OF
SHOWERS WILL DECREASE THROUGH OUT THE DAY AS THE TROUGH TRACKS INTO
NORTHERN CA WITH HIGH PRES BUILDING IN FROM THE WEST.

HAVE REMOVED MENTION OF THUNDERSTORMS OVER THE LANE COUNTY CASCADES
THIS AFTERNOON. MODEL SOUNDING AND INSTABILITY INDICIES DO NOT
SUPPORT CONVECTION...AS WELL A WESTERLY FLOW AT MID AND UPPER LEVELS.

FOR FRIDAY...BUILDING 500MB HEIGHTS TONIGHT AND FRIDAY SHOULD
RESULT IN CONDITIONS DRYING OUT CONSIDERABLY ACROSS MOST OF THE AREA.
THE LONE EXCEPTION TO THIS WILL BE ACROSS EXTREME NORTHWEST OREGON
AND SOUTHWEST WASHINGTON WHERE A DYING FRONT PUSHING INTO THE REGION
FROM THE NORTHWEST MAY BRING A SHOWER OR TWO FRIDAY. FRIDAY NIGHT
APPEARS TO BE THE TRANSITION FROM ONSHORE TO OFFSHORE DRYING.

FOR SATURDAY...THERMAL LOW PRESSURE OVER NORTHERN CALIFORNIA WILL
BUILD NORTHWARD UP THE COAST...BRINGING INCREASING OFFSHORE FLOW AND
A RETURN TO MUCH WARMER TEMPERATURES. AREAS OF SMOKE WILL ONCE AGAIN
BECOME A CONCERN OVER THE WILLAMETTE VALLEY DURING THIS PERIOD.
/NEUROCKMAN /26


.LONG TERM...SUNDAY THROUGH WEDNESDAY...SUNDAY WARM TEMPERATURES
WILL CONTINUE DUE TO CONTINUED EASTERLY FLOW. SUNDAY AFTERNOON WINDS
WILL SHIFT TO MORE SOUTHWESTERLY WITH A MARINE SURGE ALONG THE COAST
BRINGING CLOUDS BACK TO THE COAST. SOUTHWESTERLY WINDS AND MARINE-
SOURCED AIR WILL COOL TEMPERATURES FOR MONDAY AND TUESDAY AHEAD OF
OUR NEXT WEATHER SYSTEM...AN UPPER-LEVEL TROUGH APPROACHING THE WEST
COAST ON MONDAY. THE GFS...ECMWF...AND DGEX ARE IN GOOD AGREEMENT
THAT WHILE THE LONGWAVE TROUGH STALLS IN THE GULF OF ALASKA...A
SERIES OF SHORTWAVES SOURCING FROM THE PARENT LOW OFF THE WEST COAST
WILL BRING SEVERAL CHANCES FOR RAIN ACROSS OUR AREA TUESDAY AND
WEDNESDAY. THE MODELS RECENTLY HAVE TENDED TO GENERATE A LOT OF
MOISTURE FURTHER IN THE FORECAST PERIOD...THEN BACK OFF AS THE EVENT
APPROACHES. FOR THIS REASON...I AM HESITANT TO COMMIT TO THIS BEING
A PRODUCTIVE RAINFALL EVENT. -MCCOY
&&

.AVIATION...A LOW PRESSURE SYSTEM REMAINS OFF THE COAST THIS
MORNING...WITH CONSIDERABLE CLOUDS SPREADING ACROSS SOUTHWEST
WASHINGTON AND NORTHWEST OREGON IN SOUTH TO SOUTHWEST FLOW ALOFT
WITH A FEW SHOWERS. THE UPPER TROUGH AXIS WILL MOVE ONSHORE TODAY
AND EAST OF THE CASCADES LATE TODAY AND THIS EVENING. CIGS MAY
LOWER A BIT AS THIS HAPPENS...BUT CONDITIONS LOOK TO STAY MOSTLY
VFR. THE COAST MAY SEE SOME LOCAL MVFR CIGS DEVELOP AS THE TROUGH
MOVES ONSHORE. ONSHORE FLOW BEHIND THE SYSTEM WILL LIKELY RESULT
IN MVFR CONDITIONS DEVELOPING AT THE COAST TONIGHT...SPREADING
INLAND LATE TONIGHT AND FRIDAY MORNING. A WEAK SYSTEM MAY BRING
SOME LIGHT PRECIPITATION TO KAST LATE TONIGHT AND FRIDAY MORNING
AS WELL.

KPDX AND APPROACHES...VFR CIGS TODAY...WITH A FEW SHOWERS AROUND.
POSSIBLE MVFR CIGS LATE TONIGHT...AROUND 10Z TO 12Z...CONTINUING
THROUGH FRIDAY MORNING. PT
&&

.MARINE...WINDS ARE EXPECTED TO REMAIN BELOW SMALL CRAFT CRITERIA
THROUGH FRIDAY MORNING. THERMAL LOW PRESSURE IS EXPECTED TO
DEVELOP ALONG THE NORTHERN CALIFORNIA COAST LATE FRIDAY AND EXTEND
NORTH ALONG THE FRIDAY NIGHT INTO SATURDAY...WITH POTENTIAL SMALL
CRAFT ADVISORY NORTHERLIES SPREADING NORTH THROUGH THE WATERS.
WINDS WILL DECREASE SATURDAY NIGHT...BUT A SOUTHERLY WIND REVERSAL
WILL SPREAD UP THE COAST SATURDAY NIGHT AND SUNDAY. WINDS MIGHT
GUST TO 15 OR EVEN 20 KT.

SEAS ARE EXPECTED TO BE AROUND 6 FT TODAY AND 5 FT FRIDAY WITH A
MIXTURE OF 16 TO 18 SECOND SOUTHWEST SWELL AND AROUND 10 SECOND
NORTHWEST SWELL. SEAS THEN BUILD TO AROUND 8 FT SATURDAY IN THE
STRENGTHENING NORTHERLIES...DROPPING BACK DOWN TO AROUND 5 FT
SUNDAY. PT
&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
PZ...NONE.
&&

$$

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 AS THE FORECAST AREA.


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