418
FXUS66 KSEW 112220
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
320 PM PDT SUN OCT 11 2026
SYNOPSIS
DRY NORTHEASTERLY FLOW WILL MAINTAIN CLEAR SKIES WITH MORNING
FROST AND FOG THROUGH MONDAY AS TEMPERATURES RETURN TO NEAR-
NORMAL. CHANCES FOR RAIN INCREASE TOWARDS THE MIDDLE OF THE
WEEK AS A WEAK ATMOSPHERIC RIVER TAKES AIM AT BRITISH COLUMBIA
AND SHIFTS SOUTHWARD. AN UPPER LEVEL RIDGE WILL BRING WARMER AND
DRIER CONDITIONS TOWARDS THE END OF THE WORK WEEK. COOLER AND
UNSETTLED CONDITIONS MAY RETURN BY NEXT WEEKEND AS ANOTHER
WEATHER SYSTEM APPROACHES THE PACIFIC NORTHWEST.
SHORT TERM /TODAY THROUGH TUESDAY NIGHT/
DRY NORTHEASTERLY FLOW ALOFT IN THE WAKE OF AN EXITING UPPER
LEVEL LOW WILL CONTINUE TO PROMOTE CLEAR SKIES, ALLOWING DAYTIME
TEMPERATURES TO REACH A FEW DEGREES ABOVE YESTERDAY. HIGHS TODAY
ARE ON TRACK TO TOP OUT IN THE UPPER 50S TO LOWER 60S, GENERALLY
A DEGREE OR TWO SHY OF SEASONAL NORMALS. CLEAR SKIES TONIGHT
WILL CONTINUE TO PROMOTE COLDER OVERNIGHT LOWS, WITH WEAK WINDS
ALLOWING FOR THE FORMATION OF FROST AND PATCHY FOG IN THE EARLY
MORNING HOURS. A FROST ADVISORY REMAINS IN EFFECT THROUGH MONDAY
MORNING FOR MUCH OF THE PUGET SOUND AREA SOUTHWARD, THE HOOD
CANAL, AND THE NORTH COAST TO SIGNAL THE END OF THE GROWING
SEASON IN THESE AREAS. CONTINUED DRY NORTHEASTERLY FLOW WILL
ALLOW FOR SLIGHTLY WARMER TEMPERATURES ON MONDAY, WITH MOST
INLAND AREAS SURPASSING 60 DEGREES.
AS A WEAK ATMOSPHERIC RIVER TAKES AIM AT BRITISH COLUMBIA, THE
INFLUX OF MOISTURE WILL BRING INCREASED CLOUDS OVER WESTERN
WASHINGTON MONDAY NIGHT, POTENTIALLY LIMITING FOG AND FROST
DEVELOPMENT EARLY TUESDAY MORNING. WHILE MOST OF THE RAINFALL
WITH THIS SYSTEM IS EXPECTED TO STAY NORTH OF THE CANADA BORDER,
RAIN MAY CLIP THE NORTHWESTERN OLYMPIC PENINSULA AND NORTHERN
INTERIOR ON TUESDAY. TEMPERATURES WILL STAY FAIRLY STEADY INTO
TUESDAY, WITH MOST INLAND AREAS ONCE AGAIN SEEING HIGHS NEAR OR
ABOVE 60 DEGREES.
LONG TERM /WEDNESDAY THROUGH SATURDAY/
THE DECAYING ATMOSPHERIC RIVER SYSTEM WILL SHIFT SLIGHTLY
SOUTHWARD ON WEDNESDAY, BUT AN UPPER LEVEL RIDGE BUILDING ALONG
THE SOUTHWESTERN PACIFIC COAST MAY KEEP MOST OF THE REGION ON
THE DRY SIDE. CHANCES FOR RAIN WILL BE HIGHEST ONCE AGAIN OVER
THE OLYMPIC PENINSULA AND NORTHERN INTERIOR, THOUGH THE
FORECASTED PATH OF THE ATMOSPHERIC RIVER MAY SHIFT AS THE EVENT
DRAWS CLOSER. THE UPPER LEVEL RIDGE WILL CONTINUE TO BUILD
NORTHWARD INTO WESTERN WASHINGTON ON THURSDAY AND FRIDAY, THOUGH
THE WARMING AND DRYING TREND MAY BEGIN AS EARLY AS WEDNESDAY.
TEMPERATURES WILL RISE WELL ABOVE NORMAL, WITH HIGHS SET TO
REACH THE UPPER 60S TO LOWER 70S BY FRIDAY. SOME AREAS IN THE
CASCADE VALLEYS INCLUDING THE HIGHWAY 12 CORRIDOR MAY EVEN SEE
HIGHS IN THE UPPER 70S. HOWEVER, NO DAILY TEMPERATURE RECORDS
ARE EXPECTED TO BE BROKEN, AS OCTOBER 16TH WAS ONE OF THE
WARMEST OCTOBER DAYS ON RECORD IN 2022 AT 88 DEGREES IN SEATTLE.
BY SATURDAY, THE UPPER LEVEL RIDGE IS EXPECTED TO BE WELL TO THE
EAST AS TROUGHING DEVELOPS OVER THE PACIFIC NORTHWEST. THIS WILL
LIKELY BRING IN CHANCES FOR RAIN AND COOLER TEMPERATURES, THOUGH
THE EXACT DETAILS REMAIN UNCERTAIN AT THIS TIME.
15
AVIATION
WIDESPREAD VFR CONDITIONS THIS AFTERNOON. CONDITIONS EXPECTED TO
TREND VFR INTO MONDAY MORNING FOR THE MAJORITY OF TERMINALS.
HOWEVER, CLEAR SKIES AND LIGHT WINDS WILL BRING THE THE CHANCE (25-
35%) FOR LIFR LOW CLOUDS AND FOG FOR THE SOUTHERN INTERIOR AND
VALLEYS. ADDITIONALLY, WHILE THERE IS UNCERTAINTY IN HOW LOW
TEMPERATURES WILL GET TONIGHT, TEMPERATURES MAY REACH FREEZING BY
MONDAY MORNING, WHICH BRINGS THE RISK FOR FREEZING FOG. BREEZY
NORTHERLY WINDS THIS AFTERNOON ACROSS THE NORTHERN INTERIOR AND
PUGET SOUND TERMINALS WILL EASE THIS EVENING. WINDS WILL SHIFT
SOUTHERLY MONDAY MORNING, BEFORE SHIFTING NORTHERLY AGAIN MONDAY
AFTERNOON.
KSEA...VFR CONDITIONS WILL PREVAIL TODAY AND TOMORROW WITH MOSTLY
CLEAR SKIES. FOG MAY DEVELOP NEAR THE TERMINAL IN THE ADJACENT
VALLEYS, HOWEVER IT IS EXPECTED TO DIRECTLY IMPACT THE TERMINAL.
BREEZY NORTHERLY TO NORTHEASTERLY WINDS WILL EASE LATE THIS EVENING
TO 5 KT OR LESS. WINDS SHIFT SOUTHEASTERLY MONDAY MORNING AFTER 11Z
AT 3-5 KT, THEN SHIFTING WEST-NORTHWESTERLY IN THE AFTERNOON AROUND
21Z AT 5-7 KT.
29
MARINE
WINDS WILL EASE LATER TODAY ACROSS THE NORTHERN INLAND WATERS AND
PUGET SOUND AS HIGH PRESSURE SETTLED OVER BRITISH COLUMBIA WEAKENS
TODAY. BROAD HIGH PRESSURE OVER THE PACIFIC WILL EXPAND INTO AREA
WATERS ON MONDAY AND STRENGTHEN LATE IN THE WEEK. A WEAK FRONT WILL
MOVE ACROSS THE WATERS LATE TUESDAY INTO WEDNESDAY WITH LITTLE TO NO
IMPACTS. SEAS GENERALLY 5-8 FEET INTO NEXT WEEK, AND MAY GET STEEP
AT TIMES EARLY IN THE WEEK.
29
SEW WATCHES/WARNINGS/ADVISORIES
WA...FROST ADVISORY FROM MIDNIGHT TONIGHT TO 8 AM PDT MONDAY FOR
EASTERN KITSAP COUNTY-FOOTHILLS AND VALLEYS OF PIERCE AND
SOUTHERN KING COUNTIES-FOOTHILLS AND VALLEYS OF THURSTON
AND LEWIS COUNTIES-FOOTHILLS OF THE WESTERN AND SOUTHERN
OLYMPIC PENINSULA-LAKE CRESCENT AREA INCLUDING US 101-
LOWLANDS OF LEWIS AND SOUTHERN THURSTON COUNTIES-LOWLANDS
OF PIERCE AND SOUTHERN KING COUNTIES-MIDDLE CHEHALIS
RIVER VALLEY-NORTHERN HOOD CANAL-NORTHERN WASHINGTON
COAST-OLYMPIA AND SOUTHERN PUGET SOUND-SOUTHERN HOOD
CANAL-WILLAPA AND BLACK HILLS.
PZ...NONE.
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