797
FXUS66 KSEW 180333
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
833 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/
THE LATEST FORECAST REMAINS ON TRACK THIS EVENING WITH NO
UPDATES. 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
LOW LEVEL ONSHORE FLOW WILL GRADUALLY WEAKEN THIS AFTERNOON INTO
TONIGHT THEN BECOME NORTHERLY OR WEAKLY OFFSHORE ON SUNDAY. 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. NORTHERLY SURFACE WINDS SUNDAY AFTERNOON
5-10 KT.
KSEA...VFR CONDITIONS TONIGHT, CONTINUING ON SUNDAY. CONFIDENCE
REMAINS FAIRLY HIGH THAT SOME LIFR FOG AND LOW CLOUDS WILL BE AROUND
THE TERMINAL ON SUNDAY MORNING BEFORE SCATTERING OUT BY AFTERNOON.
ELEVATED NE SURFACE WINDS THIS EVENING BETWEEN 10-14 KT SHOULD
DECREASE TONIGHT TO 5-7 KT. WINDS WILL SHIFT N/NW SUNDAY AFTERNOON
AND INCREASE TO 7-10 KT.
27/29
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...NONE.
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