140
FXUS66 KSEW 100940
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
240 AM PDT THU SEP 10 2026
SYNOPSIS
UPPER LEVEL RIDGING PROGRESS OFF AND AWAY ON THURSDAY AS
TROUGHING DEVELOPS OVER THE PACIFIC NORTHWEST LATE THIS WEEK. AN
UPPER LOW PROGRESSES ACROSS THE REGION OVER THE WEEKEND
BRINGING RAIN POTENTIAL AND COOLER TEMPERATURES. DRIER
CONDITIONS ARE EXPECTED ON MONDAY WITH A SLOW WARMING TREND
THROUGH MIDWEEK.
SHORT TERM /TODAY THROUGH SATURDAY/
THE UPPER-RIDGE THAT BROUGHT SLIGHTLY ABOVE AVERAGE
TEMPERATURES YESTERDAY HAS PROGRESSED OFF AND AWAY WELL EAST OF
THE CASCADES THIS MORNING. AN UPPER-TROUGH IS NOW REPLACING IT
AS LOW-LEVEL ONSHORE FLOW INCREASES ACROSS WESTERN WA. THE FLOW
REVERSAL IS READILY APPARENT ON SATELLITE AS OF 0900Z WITH
MARINE STRATUS SNAKING THROUGH THE STRAIT OF JUAN DE FUCA. AS A
RESULT, AREAS OF STRATUS AND COOLER TEMPERATURES ARE IN STORE
FOR TODAY. HIGH TEMPERATURES ARE TO REMAIN IN THE LOWER TO MID
70S ACROSS THE INTERIOR, 5-10 DEGREES COOLER COMPARED TO THE
PREVIOUS DAY'S WITH COASTAL AREAS IN THE 60S. ZONAL FLOW IN THE
850 MB LEVELS WILL LEAD TO WEAK CONVERGENCE LATER TONIGHT ACROSS
SNOHOMISH COUNTY. OVERNIGHT LOWS ARE TO RANGE BETWEEN THE UPPER
50S TO MID 50S.
TROUGHING FURTHER DEEPENS FRIDAY AS AN UPPER-LOW DEVELOPS
OFFSHORE OF VANCOUVER ISLAND. AREAS OF DRIZZLE MAY ALSO EXIST
FRIDAY MORNING ASSOCIATED WITH WIDESPREAD STRATUS, HOWEVER,
FRIDAY IS EXPECTED TO REMAIN PREDOMINANTLY DRY WITH THE UPPER
LOW WELL OFFSHORE. POPS WILL INCREASE ON SATURDAY ACROSS THE CWA
AS THE UPPER-LOW MOVES ONSHORE WITH WIDESPREAD RAIN AND SHOWERS.
THERE IS ALSO A 15 TO 25% PROBABILITY OF THUNDERSTORMS SOUTH OF
SNOHOMISH COUNTY SATURDAY AFTERNOON. CAN'T RULE OUT LOCALLY
BREEZY WIND AT TIMES. HIGHS FOR BOTH FRIDAY AND SATURDAY BOTH IN
THE 60S WITH LOWS IN THE 50S.
LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/
THE UPPER LOW CONTINUES TO DRIFT EASTWARD ON SUNDAY,
WITH A SLOW DRYING TREND DURING THE EVENING. THE EXCEPTION
BEING THE CASCADES WHERE LINGERING MOISTURE IS EXPECTED AT LEAST
THROUGH SUNDAY AM. AN UPPER RIDGE BEGINS TO BUILD WELL OFFSHORE
MONDAY FOR A SLOW WARMING TREND. PREDOMINANTLY DRY CONDITIONS
ARE THEN FORECAST INTO THE MIDDLE OF NEXT WEEK, BUT WILL NEED TO
MONITOR THE EXISTENCE OF ANY WEAK TROUGHING AROUND THE TUESDAY
TIMEFRAME AS INDICATED BY A SMALL SUBSET OF ENSEMBLES. EITHER
WAY, TEMPERATURES TREND BACK TO NEAR NORMAL EARLY NEXT WEEK.
AVIATION
GENERALLY VFR ACROSS WESTERN WASHINGTON EARLY THIS MORNING, WITH
DETERIORATED MVFR TO IFR CONDITIONS EXPECTED AROUND 12Z-14Z AS A
FRONTAL SYSTEM BRINGS A MARINE STRATUS LAYER INLAND. LOW CEILINGS
MAY LINGER INTO THE EARLY AFTERNOON TODAY, EXPECTED TO ERODE FOR
MOST INLAND TERMINALS BY 21Z TO REVEAL VFR CONDITIONS. NORTHERLY
SURFACE WINDS WILL GENERALLY REMAIN LIGHT 10 KT OR LESS THROUGH THE
TAF PERIOD. ANOTHER MARINE PUSH WILL LIKELY BRING ANOTHER ROUND OF
MVFR LOW STRATUS ACROSS THE REGION FRIDAY MORNING.
KSEA...MVFR CONDITIONS EXPECTED TO DEVELOP OVER THE TERMINAL BY 13Z-
15Z THIS MORNING AS A MARINE PUSH BRINGS IN LOW STRATUS. CONDITIONS
WILL LIKELY REMAIN DETERIORATED THROUGH THE EARLY AFTERNOON,
ESTIMATED AROUND 20Z-21Z. CONDITIONS WILL RETURN TO VFR THEREAFTER,
WITH ANOTHER POTENTIAL MARINE PUSH EARLY FRIDAY MORNING BRINGING
ANOTHER ROUND OF LOW END VFR OR MVFR CEILINGS. WINDS WILL REMAIN
NORTHERLY AROUND 5-10 KT THROUGHOUT THE DAY, FLIPPING SOUTHERLY
FRIDAY MORNING AROUND 9Z-12Z.
15
MARINE
A FRONTAL SYSTEM WILL CONTINUE TO CROSS AREA WATERS TODAY, BRINGING
BREEZY WESTERLIES THROUGH THE STRAIT OF JUAN DE FUCA AND ELEVATED
WAVES OFFSHORE. A SMALL CRAFT ADVISORY REMAINS IN EFFECT FOR THE
CENTRAL AND EASTERN STRAIT OF JUAN DE FUCA THROUGH THE MORNING, AND
A SMALL CRAFT OVER THE OUTER COASTAL WATERS FOR WAVES OF 8 TO 11
FEET AND STEEP SEAS WITH A PERIOD OF 8 TO 10 SECONDS WILL CONTINUE
THROUGH FRIDAY MORNING BEFORE SEAS BEGIN TO SUBSIDE.
ANOTHER WEATHER SYSTEM IS ON TRACK TO CROSS THE WATERS LATE FRIDAY
IN TO SATURDAY, BRINGING LITTLE IN THE WAY OF WIND BUT WILL GENERATE
SCATTERED THUNDERSTORM ACTIVITY MAINLY OVER THE COASTAL WATERS. SEAS
WILL EASE BY SATURDAY TO AROUND 4 TO 6 FEET, WHERE THEY WILL REMAIN
INTO EARLY NEXT WEEK.
SURFACE HIGH PRESSURE IS EXPECTED TO BUILD OVER AREA WATERS BY THE
END OF THE WEEKEND, MAINTAINING GENERALLY BENIGN CONDITIONS.
15
FIRE WEATHER
A WEAK AND MOSTLY DRY FRONTAL SYSTEM PASSING OVER THE REGION HAS
BROUGHT A RETURN TO ONSHORE FLOW, MAINTAINING COOLER AND MORE MOIST
CONDITIONS THROUGHOUT THE WEEKEND. LIGHT PRECIPITATION IS LIKELY
LATE FRIDAY INTO SATURDAY AS ANOTHER WEAK SYSTEM MOVES OVER THE
REGION. CONDITIONS ARE EXPECTED TO GRADUALLY WARM AND DRY INTO NEXT
WEEK, THOUGH FIRE WEATHER CONCERNS REMAIN LOW AT THIS TIME.
15
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...SMALL CRAFT ADVISORY UNTIL 8 AM PDT THIS MORNING FOR CENTRAL
U.S. WATERS STRAIT OF JUAN DE FUCA-EAST ENTRANCE U.S.
WATERS STRAIT OF JUAN DE FUCA.
SMALL CRAFT ADVISORY FROM 5 AM EARLY THIS MORNING TO 5 AM PDT
FRIDAY 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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