548
FXUS66 KSEW 090258
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
758 PM PDT TUE SEP 8 2026
SYNOPSIS
AN UPPER RIDGE OFFSHORE WILL BRING DRY, WARMER CONDITIONS THROUGH
WEDNESDAY. TROUGHING DEVELOPS OVER THE PACIFIC NORTHWEST THURSDAY
WITH AN UPPER LOW BRINGING COOLER CONDITIONS AND PRECIPITATION
POTENTIAL INTO THE WEEKEND.
SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/
MOSTLY CLEAR SKIES PREVAIL ACROSS WESTERN WASHINGTON THIS EVENING.
FORECAST TRENDS LOOK ON TRACK FOR A SMIDGE OF WARMING TOMORROW AS AN
UPPER RIDGE NUDGES INTO THE REGION BEFORE A COOLER, UNSETTLED
STRETCH FINISHES OFF THE WEEK AS A TROUGH SETTLES OVER THE PACIFIC
NORTHWEST. PREVIOUS DISCUSSION FOLLOWS WITH UPDATES TO MARINE AND
AVIATION PORTIONS. 27
MOSTLY SUNNY CONDITIONS TODAY WITH A FEW CLOUDS MAINLY OVER THE
HIGHER ELEVATIONS. AN UPPER RIDGE OFFSHORE BUILDS INTO WESTERN
WASHINGTON ON WEDNESDAY, RESULTING IN WARMER TEMPERATURES AND
CONTINUED DRY CONDITIONS. HIGHS ON WEDNESDAY ARE EXPECTED TO RANGE
IN THE 70S TO LOW 80S. THE RIDGE BEGINS TO FLATTEN WEDNESDAY NIGHT
AS TROUGHING DEVELOPS ON THURSDAY. WIDESPREAD CLOUDS THURSDAY AM
WILL RESULT IN COOLER CONDITIONS. INCREASING ONSHORE FLOW MAY ALSO
RESULT IN THE DEVELOPMENT OF WEAK CONVERGENCE BY LATE THURSDAY OVER
CENTRAL PUGET SOUND AND INTO THE CASCADES.
LONG TERM /FRIDAY THROUGH TUESDAY/
TROUGHING FURTHER DEVELOPS OVER THE PACIFIC NORTHWEST ON FRIDAY
WITH A CONTINUED COOLING TREND LATE IN THE WEEK. ENSEMBLES ARE
IN GENERAL AGREEMENT THAT AN UPPER LOW MOVES SOUTHWARDS OFFSHORE
FRIDAY BEFORE MOVING 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. JD
AVIATION
VFR CONDITIONS WILL CONTINUE ACROSS WESTERN WASHINGTON
THROUGH TONIGHT WITH MOSTLY CLEAR SKIES. MODELS ARE HINTING AT SOME
MARINE STRATUS DEVELOPMENT EARLY WEDNESDAY MORNING, BUT THE MOST
LIKELY AREA REMAIN THE COAST, WITH LESS THAN A 20-25% CHANCE
ELSEWHERE. SOME PATCHY VALLEY FOG MAY DEVELOP FOR THE MORE SHELTERED
TERMINALS AS WELL (OLM, PAE). LOW CLOUDS AND FOG WILL DISSIPATE
QUICKLY AGAIN TOMORROW MORNING, THROUGH HIGH CLOUDS WILL BEGIN TO
BUILD IN FROM THE NORTH. WINDS REMAIN NORTHERLY 10 KT OR LESS
THROUGH THE PERIOD.
KSEA...VFR CONDITIONS PREVAIL THROUGH THE TAF PERIOD. NORTHERLY
WINDS BETWEEN 3-6 KTS OVERNIGHT, INCREASING SLIGHTLY TOMORROW
AFTERNOON AT AROUND 4 TO 8 KT.
62/21
MARINE
HIGH PRESSURE WILL CONTINUE TO BUILD OVER THE COASTAL WATERS THROUGH
EARLY THURSDAY. NORTHWESTERLY WINDS WILL PREVAIL OVER THE COASTAL
WATERS, BUT WILL INCREASE MORESO WEDNESDAY NIGHT AS A WEAK FRONTAL
SYSTEM FROM THE NORTH TIGHTENS THE PRESSURE GRADIENTS. NORTHWEST
WINDS OVER THE FAR OUTER COASTAL WATERS COULD REACH UP TO AROUND 20
KT (30-50% CHC), WITH BETTER CHANCES OF SEEING SMALL CRAFT ADVISORY
WINDS BEING THROUGH PORTIONS OF THE STRAIT OF JUAN DE FUCA (60-90%
CHC). WINDS LOOK TO SLOWLY EASE THURSDAY NIGHT. ANOTHER WEATHER
SYSTEM MAY MOVE OVER THE WATERS LATE FRIDAY INTO SATURDAY, BUT NO
HEADLINE WINDS ARE ANTICIPATED AT THIS TIME.
SEAS AROUND 3 TO 5 FEET WILL GRADUALLY BUILD THROUGH WEDNESDAY,
REACHING 7 TO 10 FEET BY THURSDAY AFTERNOON. THIS WILL ALSO BRING
STEEP SEAS AS SHORT PERIOD WAVES FROM THE STRONGER WINDS OVER THE
COASTAL WATERS BEGIN TO DOMINATE. SEAS WILL EASE TO AROUND 5 TO 6
FEET BY FRIDAY, THEN FURTHER EASING INTO THE WEEKEND.
62/21
FIRE WEATHER
DRY, WARM WEATHER CONTINUES THROUGH WEDNESDAY.
GIVEN THE RECENT COOL CONDITIONS, THIS WILL GENERALLY RETURN
FIRE WEATHER CONDITIONS BACK TO SEASONAL LEVELS OF CONCERN, WITH
LOCALIZED ELEVATED CONDITIONS WEDNESDAY. LIGHT OFFSHORE FLOW
TUESDAY NIGHT INTO WEDNESDAY WILL YIELD MODERATE RH RECOVERIES
ALONG THE RIDGES OF THE CASCADES AND OLYMPICS. DAYTIME RH VALUES
WILL APPROACH THE LOW TO MID 20 PERCENT RANGE WEDNESDAY OVER
THE CASCADES AND NEARBY VALLEYS. HOWEVER, THIS PERIOD OF
WARMER, DRY CONDITIONS WILL REMAIN SHORT-LIVED AS ONSHORE FLOW
RETURNS LATER THURSDAY FOR INCREASING RH VALUES. COOLER
CONDITIONS, ALONG WITH PRECIPITATION CHANCES, THEN CONTINUES
OVER THE WEEKEND. JD
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...NONE.
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