554
FXUS66 KSEW 091649
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
949 AM PDT WED SEP 9 2026
SYNOPSIS
AN UPPER RIDGE OFFSHORE WILL BRING DRY, WARMER
CONDITIONS ON WEDNESDAY. TROUGHING DEVELOPS OVER THE PACIFIC
NORTHWEST THURSDAY WITH AN UPPER LOW BRINGING COOLER CONDITIONS
AND PRECIPITATION POTENTIAL INTO THE WEEKEND. MORE BENIGN
WEATHER APPEARS FAVORABLE INTO THE BEGINNING OF NEXT WEEK.
SHORT TERM /TODAY THROUGH FRIDAY/
MOSTLY SUNNY CONDITIONS
THIS MORNING WITH HIGH CLOUDS OVERHEAD AND LOCALIZED FOG IN
RIVER VALLEYS. TRANSIENT UPPER- RIDGING TODAY IN CONCERT WITH A
SURFACE THERMAL TROUGH JUST OFF THE PNW COAST. AS A RESULT, DRY
CONDITIONS ARE FAVORED AS LIGHT OFFSHORE FLOW AND SUBSIDENCE
RISE TEMPS INTO THE UPPER 70S TO LOWER 80S ACROSS THE INTERIOR
- SLIGHTLY ABOVE AVERAGE. COASTAL AREAS ARE TO STAY PUT IN THE
MID TO UPPER 60S. AFOREMENTIONED RIDGING AND SURFACE THERMAL
TROUGH WILL PUSH EASTWARD ON THURSDAY AS THE PATTERN PROGRESSES.
UPPER-TROUGHING WILL DEVELOP AS LOW-LEVEL FLOW SWITCHES
ONSHORE, USHERING IN MARINE STRATUS AND COOLER TEMPERATURES.
TROUGHING FURTHER DEVELOPS OVER THE PACIFIC NORTHWEST ON FRIDAY
WITH A CONTINUED COOLING TREND. ENSEMBLES ARE IN GENERAL
AGREEMENT THAT AN UPPER LOW MOVES SOUTHWARDS OFFSHORE FRIDAY
WITH AN INCREASE OF AREAS POPS. HIGHS FORECAST IN THE 60S AND
70S ON THURSDAY BEFORE SETTLING MAINLY IN THE 60S ON FRIDAY.
OVERNIGHT LOWS IN THE 40S AND 50S THROUGHOUT THE SHORT TERM.
LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/
THE UPPER-LOW WILL
MOVE INLAND OVER WA/OR DURING THE WEEKEND. RAIN POTENTIAL
INCREASES AS THE UPPER LOW MOVES INLAND, PARTICULARLY SATURDAY
INTO SATURDAY NIGHT. THERE IS ALSO A 10 TO 15 PERCENT
PROBABILITY FOR THUNDERSTORMS SATURDAY AFTERNOON. SOME
UNCERTAINTY IN THE ENSEMBLES AS TO HOW QUICKLY THE TROUGHING
MOVES EASTWARDS SUNDAY INTO MONDAY. HOWEVER, LINGERING
PRECIPITATION IS LIKELY AT LEAST OVER THE CASCADES ON SUNDAY
BEFORE A SLOW WARMING TREND BEGINS EARLY NEXT WEEK WITH RIDGING
OFFSHORE.
AVIATION
FLOW ALOFT WILL REMAIN PRIMARILY OUT OF THE
WEST/NORTHWEST AS A WEAK RIDGE MOVES EAST OF THE ROCKIES TODAY,
GIVING WAY TO A TROUGH TONIGHT/THURSDAY. MOST TERMINALS ARE VFR
THIS MORNING, WITH A COUPLE ISOLATED POCKETS OF PATCHY POCKETS
OF LOW IFR/LIFR STRATUS AFFECTING THE PRIMARY PUGET SOUND
TERMINALS THIS MORNING, AND JUST WEST OF BELLINGHAM. WIDESPREAD
STRATUS HAS HELD OFF THE COAST. THE PATCHY POCKETS WILL HANG
AROUND THROUGH 16-17Z. SKY COVERAGE TODAY WILL PRIMARILY BE VFR
(OUTSIDE OF THE PATCHY STRATUS THIS MORNING), WITH MID AND HIGH
LEVEL CLOUDS ROLLING IN THIS EVENING AHEAD OF THE TROUGH. THE
TROUGH AND INCREASE OF ONSHORE WILL LIKELY LEAD TO SOME MVFR
CEILINGS FOR MOST THURSDAY MORNING, FORMING FROM 12Z AND
POTENTIALLY HOLDING OVER THROUGH 21Z BEFORE IMPROVEMENT TO VFR.
THE COAST HAS A 30-40% CHANCE OF IFR CONDITIONS WITH THE INITIAL
STRATUS ONSET, AND A 20% CHANCE OF LIFR. WINDS WILL REMAIN
NORTHERLY TODAY AT 5-10 KT, BECOMING 5 KT OR LESS OUT OF THE
WEST GOING INTO THURSDAY.
KSEA...PATCHY LIFR STRATUS WILL HANG OVER THE TERMINAL THROUGH 16-
17Z THEN IMPROVING TO VFR THROUGH TONIGHT (MID TO HIGH LEVEL CLOUDS
LATER THIS EVENING). 40-50% CHANCE OF MVFR STRATUS ARRIVING THURSDAY
MORNING FROM 12Z THROUGH AS LATE AS 21Z. NORTH WINDS 5-10 KT TODAY,
BECOMING LIGHT OUT OF THE WEST THURSDAY AT 5 KT.
15/HPR
MARINE
HIGH PRESSURE WILL CONTINUE TO BUILD OVER THE COASTAL
WATERS THROUGH EARLY THURSDAY, WITH A WEAK FRONTAL SYSTEM TO
THE NORTH BRINGING INCREASED NORTHWEST WINDS OVER THE COASTAL
WATERS AND A PUSH THROUGH THE STRAIT OF JUAN DE FUCA. WESTERLY
WINDS WILL REACH SMALL CRAFT STRENGTH THROUGH THE STRAIT LATE
WEDNESDAY EVENING THROUGH THURSDAY MORNING, AND A SMALL CRAFT
ADVISORY HAS BEEN ISSUED. WINDS WILL GRADUALLY EASE INTO
THURSDAY NIGHT ACROSS ALL AREA WATERS. ANOTHER WEATHER SYSTEM IS
ON TRACK TO CROSS THE WATERS LATE FRIDAY IN TO SATURDAY, BUT NO
SIGNIFICANT IMPACTS OR HEADLINES ARE ANTICIPATED AT THIS TIME.
SEAS AROUND 4 TO 5 FEET WILL CONTINUE TO GRADUALLY BUILD INTO
THURSDAY, REACHING 8 TO 11 FEET ACROSS THE OUTER WATERS. A SMALL
CRAFT ADVISORY HAS BEEN ISSUED TO ACCOUNT FOR THESE WAVES, WHICH
WILL BE STEEP WITH A PERIOD OF 8 TO 10 SECONDS. SEAS WILL EASE TO
AROUND 4 TO 6 FEET BY FRIDAY, WITH RELATIVELY CALM SEAS INTO THE
WEEKEND.
15
FIRE WEATHER
A DRYING AND WARMING TREND WILL PEAK TODAY, WITH LIGHT EASTERLY FLOW
THROUGH THE CASCADE GAPS CAUSING MODERATE OVERNIGHT HUMIDITY
RECOVERIES ALONG THE WESTERN CREST OF THE CASCADES. DAYTIME RELATIVE
HUMIDITIES ALONG THE RIDGES OF THE CASCADES AND OLYMPICS WILL BOTTOM
OUT IN THE LOW TO MID 20S, CAUSING BRIEF ELEVATED FIRE WEATHER
CONCERNS FOR THESE AREAS. HOWEVER, THIS WILL BE SHORT LIVED, WITH
ONSHORE FLOW RETURNING ON THURSDAY AS A WEAK AND MOSTLY DRY FRONTAL
SYSTEM CROSSES TO THE NORTH. COOLER AND MORE MOIST CONDITIONS WILL
RETURN OVER THE WEEKEND, WITH PERIODIC CHANCES FOR LIGHT
PRECIPITATION.
15
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...SMALL CRAFT ADVISORY FROM 11 PM THIS EVENING TO 11 AM PDT
THURSDAY 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 THURSDAY 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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