683
FXUS66 KSEW 130321
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
821 PM PDT MON OCT 12 2026
UPDATE
MID TO HIGH LEVEL CLOUD COVERAGE IS STREAMING OVERHEAD AS AN
UPPER-LEVEL RIDGE NOSES INTO BRITISH COLUMBIA. EXCLUDING THE
DEVELOPMENT OF PATCHY VALLEY FOG AND AREAS OF FROST, BENIGN
CONDITIONS ARE EXPECTED TONIGHT. NO CHANGES MADE IN THIS
EVENING'S FORECAST PACKAGE. THE PREVIOUS DISCUSSION REMAINS
BELOW ALONG WITH AN UPDATED MARINE AND AVIATION SECTION.
SYNOPSIS
A WEATHER SYSTEM MOVING INTO BRITISH COLUMBIA WILL BRUSH WESTERN
WASHINGTON ON TUESDAY, BRINGING SHOWERS TO THE PACIFIC COAST AND
THE NORTH INTERIOR INTO WEDNESDAY. A RIDGE OF HIGH PRESSURE WILL
REBUILD OVER THE AREA WEDNESDAY INTO THURSDAY, BEFORE PUSHING
INLAND ON FRIDAY. WARM TEMPERATURES ARE EXPECTED THURSDAY AND
FRIDAY AS OFFSHORE FLOW DEVELOPS. A WEAK SYSTEM WILL MOVE INTO
THE AREA ON SATURDAY, FOLLOWED BY A STRONGER SYSTEM SUNDAY INTO
MONDAY.
SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/
SATELLITE IMAGERY SHOWS SUNNY AND CLEAR SKIES ACROSS WESTERN
WASHINGTON THIS AFTERNOON, WITH AREAS OF PATCHY FOG THIS MORNING
HAVING DISSIPATED. HIGHS ARE STILL ON TRACK TO BE CLOSE TO SEASONAL
NORMS TODAY, AND ARE EXPECTED TO TOP OUT IN THE UPPER 50S TO MID
60S ACROSS THE AREA. DRY CONDITIONS WILL CONTINUE INTO TONIGHT
AS AN UPPER LEVEL RIDGE OVER THE REGION FLATTENS. A WEATHER
SYSTEM MOVING INTO BRITISH COLUMBIA TONIGHT INTO TUESDAY WILL
BRING INCREASING MID TO HIGH CLOUD COVER TO THE AREA OVERNIGHT,
BRINGING WARMER OVERNIGHT LOW TEMPERATURES TO MUCH OF WESTERN
WASHINGTON AND LIMITING THE POTENTIAL FOR FOG AND FROST FORMATION
OVERNIGHT. OVERNIGHT LOWS ARE EXPECTED TO BE IN THE UPPER 30S
TO MID 40S.
THE SYSTEM MOVING INTO BRITISH COLUMBIA WILL BRUSH WESTERN
WASHINGTON TUESDAY INTO EARLY WEDNESDAY AS THE RIDGE CONTINUES
TO WEAKEN AND THE SYSTEM SAGS SOUTHWARD. THIS WILL BRING SOME
LIGHT SHOWER ACTIVITY TO THE NORTHWESTERN PORTION OF THE AREA-
MAINLY TO THE PACIFIC COAST, THE WESTERN SLOPES OF THE OLYMPICS,
AND AREAS FROM KING COUNTY NORTHWARD. OVERALL RAINFALL AMOUNTS
WILL BE RATHER LIGHT, WITH AREAS ACROSS THE NORTHERN INTERIOR
LIKELY ONLY GETTING A FEW HUNDREDTHS OF AN INCH OF RAIN. THE
HIGHEST AMOUNTS WILL BE ALONG THE NORTH COAST, WHERE GENERALLY A
QUARTER OF AN INCH TO HALF AN INCH OF RAIN WILL BE POSSIBLE.
HIGHS ON TUESDAY WILL BE IN THE MID 50S TO MID 60S.
AN UPPER LEVEL RIDGE WILL THEN BUILD BACK INTO THE PACIFIC
NORTHWEST ON WEDNESDAY, WITH SHOWERS EXPECTED TO TAPER
THROUGHOUT THE DAY. HIGHS ARE EXPECTED TO BE IN THE LOWER TO
MID 60S ACROSS WESTERN WASHINGTON WITH MOSTLY CLOUDY CONDITIONS
IN THE MORNING BECOMING PARTLY CLOUDY BY THE AFTERNOON HOURS.
LONG TERM /THURSDAY THROUGH MONDAY/
GUIDANCE REMAINS IN STRONG AGREEMENT WITH THE UPPER LEVEL RIDGE
BUILDING OVER THE REGION ON THURSDAY. A THERMAL TROUGH WILL ALSO
BUILD NORTHWARD ALONG THE COAST AND WILL TURN THE LOW LEVEL
FLOW OFFSHORE, HELPING TO WARM AFTERNOON HIGHS INTO THE MID 60S
TO MID 70S ACROSS THE AREA. FRIDAY WILL BE THE WARMEST DAY OF
THE WEEK AS THE RIDGE AXIS PUSHES FURTHER INLAND AND OFFSHORE
FLOW PERSISTS THROUGH THE MORNING HOURS. HIGHS WILL CLIMB A
DEGREE OR TWO AND ARE AGAIN EXPECTED TO BE IN THE MID 60S TO
MID 70S- ROUGHLY 5 TO 10 DEGREES ABOVE NORMAL ACROSS THE AREA.
OVERNIGHT LOWS BOTH THURSDAY AND FRIDAY WILL BE IN THE MID 40S
TO LOW 50S.
A DISSIPATING FRONTAL SYSTEM THEN LOOKS TO MOVE INTO THE AREA ON
SATURDAY AS THE RIDGE AXIS PUSHES FURTHER TO THE EAST. THE BEST
CHANCES FOR RAIN REMAIN ALONG THE PACIFIC COAST AND ACROSS THE
NORTH CASCADES AS THE SYSTEM MOVES OVER THE AREA. A STRONGER,
MORE ORGANIZED FRONTAL SYSTEM THEN LOOKS TO MOVE THROUGH THE
REGION SUNDAY INTO MONDAY, BRINGING MORE WIDESPREAD CHANCES OF
RAIN AND BREEZY WINDS TO WESTERN WASHINGTON. A DUSTING OF SNOW
FOR THE HIGHER PEAKS WILL ALSO BE POSSIBLE ON MONDAY AS SNOW
LEVELS DROP TO 5000-5500 FT. HIGHS WILL COOL OVER THE WEEKEND AS
CONDITIONS BECOME MORE UNSETTLED AND ONLY LOOK TO TOP OUT IN
THE UPPER 50S TO MID 60S. OVERNIGHT LOWS WILL GENERALLY BE IN
THE 40S AND 50S.
14
AVIATION
WIDESPREAD VFR THIS EVENING WITH INCREASING HIGH CLOUDS FROM THE
NORTHWEST. CEILINGS WILL GRADUALLY DETERIORATE ALONG THE COASTLINE
OVERNIGHT INTO EARLY TUESDAY MORNING, WITH MVFR CEILINGS EXPECTED
ALONG THE COAST BY THE AFTERNOON TUESDAY. OTHERWISE, INTERIOR
TERMINALS EXPECTED TO REMAIN VFR WITH HIGH CLOUDS EXPECTED TO LIMIT
FOG DEVELOPMENT IN THE MORNING. LIGHT NORTHERLY SURFACE WINDS THIS
EVENING WILL SHIFT SOUTHERLY BY TUESDAY MORNING AND WILL REMAIN
LIGHT THROUGH THE AFTERNOON.
KSEA...VFR WITH INCREASING CLOUD COVER TONIGHT, EXPECTED TO LIMIT
FOG DEVELOPMENT AND KEEP CONDITIONS VFR INTO TUESDAY. INCREASING
CHANCES FOR MVFR CEILINGS DEVELOPING EARLY WEDNESDAY MORNING.
GENERALLY LIGHT AND VARIABLE WINDS THIS EVENING WILL SHIFT
SOUTHEASTERLY BY 06Z THIS EVENING.
MARINE
A WEAK SURFACE RIDGE WILL SHIFT INLAND ON TUESDAY AS A FRONTAL
SYSTEM APPROACHES THE OFFSHORE WATERS WITH WINDS SHIFTING TO THE
E/SE ACROSS MUCH OF THE WATERS. A WEAK COLD FRONT WILL REACH THE
AREA ON WEDNESDAY WITH POSSIBLE HEADLINES FOR LOW END SMALL CRAFT
ADVISORY WINDS ACROSS PORTIONS OF THE COASTAL WATERS AND THE WEST
ENTRANCE TO THE STRAIT OF JUAN DE FUCA. HIGH PRESSURE REBUILDS
ACROSS THE WATERS ON THURSDAY WITH THE FLOW TURNING NORTHERLY OR
WEAKLY OFFSHORE AS THERMALLY INDUCED LOW PRESSURE EXPANDS NORTHWARD
ACROSS WESTERN OREGON. ANOTHER FRONT IS EXPECTED TO REACH THE WATERS
FRIDAY NIGHT OR SATURDAY WITH POSSIBLE HEADLINES FOR WINDS AND/OR
STEEPENING SEAS ACROSS THE COASTAL WATERS. ADDITIONALLY, GUIDANCE
INDICATES POSSIBLE HEADLINES FOR THE STRAIT ON SATURDAY WITH GUSTS
HAVING A 50-60% CHANCE OF REACHING SMALL CRAFT THRESHOLDS.
SEAS WILL REMAIN AROUND 4 TO 7 FEET THROUGHOUT MUCH OF THE WEEK
BEFORE BUILDING TO 8 TO 11 FEET BY SUNDAY AND REMAINING ELEVATED
INTO EARLY NEXT WEEK.
15
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...NONE.
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