939
FXUS66 KSEW 172056
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
156 PM PDT SAT OCT 17 2026
SYNOPSIS
WEAK RIDGING BUILDS INTO WESTERN WASHINGTON EARLY
SUNDAY. AN UPPER TROUGH DIGS SOUTHWARDS ALONG THE COAST LATE
SUNDAY INTO MONDAY. RIDGING BUILDS BACK INTO THE NORTHERN
PACIFIC NORTHWEST TUESDAY AND WEDNESDAY. TROUGHING RETURNS LATE
WEEK.
SHORT TERM /TONIGHT THROUGH MONDAY NIGHT/
A POST-FRONTAL
AIRMASS CONTINUES THIS AFTERNOON WITH PREDOMINANTLY MOSTLY SUNNY
CONDITIONS. THE EXCEPTION BEING AN AREA OF WEAK CONVERGENCE
THAT CONTINUES OVER PORTIONS OF CENTRAL PUGET SOUND. DRIER
CONDITIONS WILL CONTINUE TO DEVELOP INTO TONIGHT AS CLOUDS TAPER
OFF THIS EVENING. MOSTLY CLEAR SKIES AND LIGHTER WINDS EARLY
SUNDAY AM WILL PROMOTE FOG DEVELOPMENT, PARTICULARLY IN THE
USUAL AREAS AND RIVER VALLEYS.
A WEATHER SYSTEM APPROACHES THE WEST COAST LATE SUNDAY AND
MONDAY WITH THE BULK OF THE ENERGY DIGGING SOUTHWARDS TOWARDS
CALIFORNIA EARLY NEXT WEEK. DRY CONDITIONS CONTINUE ON MONDAY
DUE TO THE SYSTEM BEING WELL OFFSHORE. CLOUDS WILL SPREAD ACROSS
WESTERN WASHINGTON DURING THIS PERIOD. OTHERWISE, HIGHS WILL BE
IN THE MID 50S TO LOW 60S SUNDAY AND MONDAY.
LONG TERM /TUESDAY THROUGH SATURDAY/
UPPER RIDGING DEVELOPS
OVER BRITISH COLUMBIA TUESDAY AND WEDNESDAY WITH AN UPPER LOW
POSITIONED WELL SOUTH OF WESTERN WASHINGTON, MAINLY OFFSHORE OF
CENTRAL CALIFORNIA. DRY CONDITIONS ARE EXPECTED TUESDAY AND
WEDNESDAY. AM FOG WILL DEVELOP AGAIN BOTH TUESDAY AND WEDNESDAY
MORNING WITH RELATIVELY LIGHT WINDS AND CLEARER SKIES. IN
ADDITION, AREAS OF FROST ARE EXPECTED EACH MORNING, MAINLY AWAY
FROM THE WATER. ENSEMBLES ARE CONSISTENT IN THE RETURN OF WEAK
TROUGHING THURSDAY INTO LATE WEEK, BRINGING PRECIPITATION
CHANCES TO THE AREA, ALTHOUGH RAINFALL AMOUNTS ARE NOT HEAVY DUE
TO THE WEAKENING NATURE OF ANY FRONTAL SYSTEM. TEMPERATURES
LOOK TO REMAIN NEAR NORMAL DURING THIS PERIOD, WITH HIGHS
PEAKING MIDWEEK. JD
AVIATION
WEST TO NORTHWEST FLOW ALOFT WILL CONTINUE INTO
SUNDAY MORNING BEFORE BACKING SOUTHWESTERLY IN RESPONSE TO AN
UPPER TROUGH DIVING SOUTHWARD OVER THE OFFSHORE WATERS. LOW
LEVEL ONSHORE FLOW WILL GRADUALLY WEAKEN THIS AFTERNOON INTO
TONIGHT THEN BECOME NORTHERLY OR WEAKLY OFFSHORE ON SUNDAY.
CEILINGS WITHIN WHAT IS LEFT OF THE CONVERGENCE ZONE ARE MOSTLY
VFR THIS AFTERNOON AND WILL CONTINUE TO LIFT AND SCATTER OUT
THIS AFTERNOON AND EVENING. LIGHT SURFACE WINDS AND LOW LEVEL
MOISTURE WILL LEAD TO THE FORMATION OF IFR/LIFR FOG AND LOW
CLOUDS ON SUNDAY MORNING...ESPECIALLY ACROSS THE SOUTHWEST
INTERIOR AND SOUTH PORTIONS OF PUGET SOUND. LOW CLOUDS WILL LIFT
FOR ANOTHER VFR AFTERNOON ON SUNDAY UNDER VARYING AMOUNTS OF
HIGH LEVEL CLOUD COVER.
KSEA...VFR CEILINGS REMAIN THIS AFTERNOON UNDER THE REMNANTS OF A
CONVERGENCE ZONE. EXPECT THIS TO LIFT AND SCATTER OUT LATE THIS
AFTERNOON AND EVENING. CONFIDENCE REMAINS FAIRLY HIGH THAT SOME LIFR
FOG AND LOW CLOUDS WILL BE AROUND THE TERMINAL ON SUNDAY MORNING
BEFORE SCATTERING OUT BY AFTERNOON. SURFACE WINDS GENERALLY N/NE 5
TO 8 KNOTS.
27
MARINE
SURFACE HIGH PRESSURE WILL BUILD ACROSS THE WATERS
TONIGHT INTO SUNDAY IN THE WAKE OF A FRONTAL SYSTEM THAT MOVED
ACROSS THE WATERS EARLIER TODAY. A LOW PRESSURE SYSTEM PASSING
SOUTHWARD WELL OFFSHORE WILL TURN WINDS NORTHERLY OR WEAKLY
OFFSHORE SUNDAY INTO MONDAY. WEAK HIGH PRESSURE WILL REMAIN
ACROSS THE WATERS INTO THE MIDDLE OF THE COMING WEEK FOR RATHER
QUIET CONDITIONS. A LARGER SWELL TRAIN NEAR 10 FEET GENERATED BY
ACTIVE WEATHER WELL OFFSHORE IS EXPECTED TO REACH THE COASTAL
WATERS AROUND THURSDAY.
27
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...SMALL CRAFT ADVISORY UNTIL 6 PM PDT THIS EVENING FOR CENTRAL
U.S. WATERS STRAIT OF JUAN DE FUCA-EAST ENTRANCE U.S.
WATERS STRAIT OF JUAN DE FUCA.
SMALL CRAFT ADVISORY UNTIL 8 PM PDT THIS EVENING FOR COASTAL
WATERS FROM CAPE FLATTERY TO JAMES ISLAND 10 TO 60 NM-
COASTAL WATERS FROM JAMES ISLAND TO POINT GRENVILLE 10 TO
60 NM-COASTAL WATERS FROM POINT GRENVILLE TO CAPE
SHOALWATER 10 TO 60 NM.
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