068
FXUS66 KSEW 092122
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
222 PM PDT WED SEP 9 2026
SYNOPSIS
UPPER LEVEL RIDGING WILL FLATTEN INTO 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 NEXT WEEK.
SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/
MOSTLY SUNNY
CONDITIONS THIS AFTERNOON WITH HIGH CLOUDS OVERHEAD. AN UPPER
RIDGE OVER THE REGION WILL FLATTEN TONIGHT WITH TROUGHING
DEVELOPING INTO THURSDAY. ONSHORE FLOW INCREASES INTO THURSDAY
RESULTING IN COOLER TEMPERATURES AND INCREASED CLOUDS. WEAK
CONVERGENCE THURSDAY EVENING INTO THURSDAY NIGHT MAY RESULT IN
AREAS OF DRIZZLE OR LIGHT RAIN ACROSS PORTIONS OF THE CENTRAL
CASCADES. TROUGHING FURTHER DEEPENS FRIDAY AS AN UPPER LOW
DEVELOPS OFFSHORE OF VANCOUVER ISLAND. DRIZZLE MAY ALSO EXIST
FRIDAY MORNING ASSOCIATED WITH WIDESPREAD STRATUS, HOWEVER,
FRIDAY IS EXPECTED TO REMAIN PREDOMINANTLY DRY WITH THE UPPER
LOW WELL OFFSHORE. TEMPERATURES WILL PEAK THIS AFTERNOON IN THE
70S TO LOW 80S, WITH HIGHS ONLY REACHING THE MID 60S TO LOW 70S
BY FRIDAY.
LONG TERM /SATURDAY THROUGH WEDNESDAY/
THE UPPER LOW OFFSHORE
WILL MOVE INLAND OVER WASHINGTON AND OREGON ON SATURDAY. THERE
REMAINS SOME UNCERTAINTY IN ENSEMBLES REGARDING THE EXACT TRACK
OF THE UPPER LOW, LEADING TO SOME SPREAD IN THE QPF AMOUNTS, AS
WELL AS THE TIMING OF RAINFALL. AT THIS TIME, RAINFALL AMOUNTS
ARE HEAVIEST SOUTH OF SNOHOMISH COUNTY, PARTICULARLY IN THE
SOUTHERN CASCADES, WITH QPF AMOUNTS AROUND 0.50" OVER MT.
RAINIER AREA ON THE NBM. IN ADDITION, THERE IS ALSO A 15 TO 25%
PROBABILITY OF THUNDERSTORMS SOUTH OF SNOHOMISH COUNTY SATURDAY
AFTERNOON. THE UPPER LOW CONTINUES TO DRIFT EASTWARD ON SUNDAY,
WITH A SLOW DRYING TREND DURING THE DAY. 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. JD
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. TERMINALS ARE VFR THIS
AFTERNOON, WITH HIGH CLOUDS EXPECTED TO FILL IN GOING INTO THE
EVENING, WITH MID AND LOWER CLOUDS TONIGHT/THURSDAY MORNING. THE
TROUGH AND INCREASE OF ONSHORE WILL LIKELY LEAD TO WIDESPREAD
MVFR CEILINGS FOR MOST TERMINALS THURSDAY MORNING, FORMING FROM
12Z AND POTENTIALLY STICKING THROUGH 21Z BEFORE IMPROVING 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. THE STRAIT OF JUAN DE FUCA AREA
WILL SEE HIGHER GUSTS TONIGHT/THURSDAY EXCEEDING 20 KT.
KSEA...VFR THROUGH TONIGHT, THEN A 40-50% CHANCE OF MVFR STRATUS
FROM 12Z THURSDAY MORNING THROUGH AS LATE AS 21Z. NORTH WINDS 5-10
KT TODAY, BECOMING LIGHT OUT OF THE WEST THURSDAY AT 5 KT.
HPR
MARINE
HIGH PRESSURE REMAINS IN THE COASTAL WATERS THROUGH
THURSDAY. AN UNSETTLED PATTERN WILL SETUP LATE THURSDAY THROUGH
THE WEEKEND AS A COUPLE OF FRONTAL SYSTEMS MOVE THROUGH THE
WATERS. THE FIRST FRONT WILL BE MOSTLY DRY (EXCEPT FOR A FEW
SHOWERS), BUT WILL PRODUCE GUSTY NORTH-NORTHWEST WINDS IN THE
OUTER COASTAL WATERS OVER 20 KT THURSDAY, AND ALSO GUSTY WEST
WINDS IN THE EASTERN STRAIT OF JUAN TONIGHT/THURSDAY MORNING AS
ONSHORE FLOW INCREASES. THE WEEKEND SYSTEM WILL PRODUCE MORE
WIDESPREAD PRECIPITATION OVER THE WATERS (PARTICULARLY ON
SATURDAY), WITH PERHAPS THE FAR SOUTHERN PUGET SOUND WATERS
HAVING A SLIGHT CHANCE (15-20%) FOR THUNDER WITH THE SHOWER
ACTIVITY. WIND IMPACTS ARE NOT ANTICIPATED AT THIS TIME WITH
THIS SYSTEM. HIGH PRESSURE WILL REBUILD OVER THE WATERS NEXT
WEEK, WITH CONDITIONS REMAINING BENIGN.
SEAS AT 4-6 FT TODAY WILL BUILD ON THURSDAY, REACHING 8-11 FT IN THE
OUTER COASTAL WATERS AND 6-8 FT FOR THE INNER WATERS. SEAS DECREASE
TO 4-6 FT FRIDAY/SATURDAY, AND 3-5 FT THIS WEEKEND INTO NEXT WEEK.
HPR
FIRE WEATHER
A DRYING AND WARMING TREND PEAKS TODAY LEADING
TO BRIEF ELEVATED FIRE WEATHER CONCERNS FOR THE CASCADES. 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 PRECIPITATION POTENTIAL ON SATURDAY INTO SUNDAY.
JD/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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