536
FXUS66 KSEW 160953
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
253 AM PDT TUE SEP 16 2025
SYNOPSIS
HIGH PRESSURE AND OFFSHORE FLOW WILL RESULT IN MUCH
WARMER TEMPERATURES TODAY ACROSS THE REGION. GUSTY EAST WINDS
THROUGH THE CASCADES AND FOOTHILLS WILL RESULT IN CRITICAL FIRE
WEATHER CONDITIONS AS WELL AS THE POTENTIAL FOR ISOLATED TREE
DAMAGE. ONSHORE FLOW RETURNS WEDNESDAY ALLOWING FOR TEMPERATURES
TO RETURN TO NEAR NORMAL. CHANCE FOR WIDESPREAD PRECIPITATION WILL
LIKELY RETURN THIS WEEKEND.
SHORT TERM /TODAY THROUGH THURSDAY/
AS A RIDGE OF HIGH PRESSURE
CONTINUES TO AMPLIFY OVER THE PACIFIC NORTHWEST, A RESULTANT
THERMAL TROUGH CONTINUES TO DEVELOP ALONG THE COAST AS AN UPPER
LOW STRENGTHENS OVER THE GULF OF ALASKA. THIS WILL GENERATE A
PERIOD OF EASTERLY CASCADE GAP WINDS TODAY, WITH THE STRONGEST
WIND GUSTS UP TO 50 MPH ALONG THE WESTERN SLOPES OF THE CASCADES AS
WELL AS THE CASCADE FOOTHILLS AND VALLEYS BETWEEN ROUGHLY
ENUMCLAW AND THE US-2 CORRIDOR. EASTERLY WINDS WILL PICK UP
THROUGH THE MORNING, PEAK MID TO LATE MORNING, AND GRADUALLY
WEAKEN THROUGHOUT THE AFTERNOON AND EVENING HOURS TODAY. WHILE
SUSTAINED WINDS ARE EXPECTED TO REACH 10 TO 20 MPH, WINDS WILL BE
GUSTY, WITH MANY AREAS SEEING GUSTS OF 35 TO 45 MPH IN THE LATE
MORNING. THE HIGHEST WIND GUSTS WILL PEAK AROUND 50 MPH, LIKELY
ALONG RIDGETOPS AND THROUGH MOUNTAIN GAPS INCLUDING ALONG THE I-90
CORRIDOR. THIS WILL RESULT IN CRITICAL FIRE WEATHER
CONDITIONS (SEE FIRE WEATHER FOR MORE DETAIL), AND WILL ALSO
RESULT IN A RISK OF TREE DAMAGE AND POWER OUTAGES, ESPECIALLY
GIVEN THE CURRENT PREVALENCE OF FOLIAGE ON TREES. AS SUCH, A WIND
ADVISORY REMAINS IN EFFECT FOR THE CENTRAL CASCADE FOOTHILL
ZONES THROUGH THIS EVENING. THE STRONG EASTERLY FLOW WILL ALSO
BRING IN MUCH WARMER AIR TO THE REGION, WITH MOST LOWLAND AREAS
SEEING HIGH TEMPERATURES IN THE 80S. THE INCREASED EASTERLY FLOW
WILL ALSO INCREASE THE RISK OF SMOKE TRANSPORT FROM THE EAST,
WHERE SEVERAL LARGE FIRES ARE PRODUCING HIGH AMOUNTS OF SMOKE.
TEMPORARY REDUCTIONS IN VISIBILITY AND AIR QUALITY ARE POSSIBLE,
BUT THE DETAILS OF WHERE AND WHEN WILL STRONGLY DEPEND ON FIRE
BEHAVIOR OVER THE NEXT 24-36 HOURS.
BY WEDNESDAY AND THURSDAY, THE UPPER LEVEL TROUGH OFFSHORE WILL
SHIFT INLAND TO BRING A RETURN OF MUCH COOLER TEMPERATURES
ALONGSIDE ONSHORE FLOW AND PARTLY CLOUDY SKIES. MOST OF THE
REGION WILL STAY DRY OUTSIDE OF SOME SPRINKLES ALONG THE COAST
WEDNESDAY.
LONG TERM /FRIDAY THROUGH MONDAY/
CONDITIONS WILL STAY MOSTLY
DRY WITH NEAR NORMAL TEMPERATURES THROUGH FRIDAY, OUTSIDE OF A
SLIGHT CHANCE OF RAIN OVER THE NORTHWEST TIP OF THE OLYMPIC
PENINSULA. THE NEXT SYSTEM IS ON TRACK TO ENTER THE PACIFIC
NORTHWEST LATER ON SATURDAY, SPREADING SEVERAL ROUNDS OF RAIN
ACROSS THE REGION THROUGH THE REMAINDER OF THE WEEKEND AND INTO
MONDAY. ENSEMBLES SHOW POTENTIAL FOR HALF AN INCH OF RAIN ACROSS
THE LOWLANDS DURING THIS TIMEFRAME, WITH AROUND 2 TO 4 INCHES OF
LIQUID OVER THE MOUNTAINS. THE EXTENDED OUTLOOK ALSO FAVORS ABOVE
AVERAGE PRECIPITATION CONTINUING INTO THE WEEK 2 TIME FRAME,
SUGGESTING A CONTINUATION OF COOL AND WET CONDITIONS ACROSS
WESTERN WASHINGTON.
15
AVIATION
UPPER LEVEL RIDGE OVER WESTERN WASHINGTON WILL SLOWLY
SHIFT EAST WITH THE RIDGE AXIS OVER NORTHERN IDAHO BY EARLY
WEDNESDAY MORNING. LIGHT FLOW ALOFT BECOMING SOUTHWESTERLY LATE
THIS MORNING. IN THE LOWER LEVELS THERMALLY INDUCED SURFACE
TROUGH ALONG THE COASTLINE WITH LOW LEVEL FLOW GOING OFFSHORE.
TROUGH SHIFTING INLAND LATER TODAY WITH LOW LEVEL FLOW GOING LIGHT
TONIGHT.
MOSTLY CLEAR SKIES THROUGH TONIGHT WITH PATCHY VALLEY FOG IN WIND
SHELTERED AREAS 13Z-17Z. GUSTY EAST WIND IN THE CASCADE FOOTHILLS
DEVELOPING THIS MORNING AND CONTINUING INTO THE AFTERNOON HOURS.
WINDS EASING TONIGHT.
KSEA...MOSTLY CLEAR SKIES. NORTHEAST WINDS 4 TO 8 KNOTS BECOMING
NORTHERLY 8 TO 12 KNOTS AFTER 21Z. WINDS SWITCHING TO
SOUTHEASTERLY 4 TO 8 KNOTS AROUND 06Z AND TO SOUTHERLY AROUND 12Z.
FELTON
MARINE
A THERMALLY INDUCED TROUGH OF LOW PRESSURE WILL EXPAND
NORTHWARD OVER THE COASTAL WATERS TODAY, WITH A WEAK FRONT
DISSIPATING OVER THE COASTAL WATERS LATER TONIGHT. HIGH PRESSURE
WILL BUILD OVER THE COASTAL WATERS WEDNESDAY AND REMAIN INTO
FRIDAY WITH LOWER PRESSURE INLAND. A FRONTAL SYSTEM WILL CROSS THE
REGION OVER THE WEEKEND.
EASTERLY WINDS OVER THE AREA WATERS TODAY WILL RESULT IN SMALL
CRAFT ADVISORY WINDS AT THE WEST ENTRANCE OF THE STRAIT OF JUAN DE
FUCA AND THE NORTHERN PORTION OF THE NORTHERN INNER COASTAL
WATERS, AS WELL AS THE SOUTHERN COASTAL WATERS BETWEEN POINT
GRENVILLE AND CAPE SHOALWATER. WINDS ALONG THE OUTERMOST OUTER
WATERS MAY ALSO REACH SCA CRITERIA WEDNESDAY AFTERNOON. WINDS
WILL EASE THEREAFTER WITH ONSHORE FLOW RESUMING THROUGH THE
REMAINDER OF THE WEEK.
SEAS WILL RANGE 4 TO 6 FEET THROUGH EARLY WEDNESDAY, BEFORE
BUILDING TO 8 TO 10 FEET LATER WEDNESDAY INTO THURSDAY, WITH
STEEPER SEAS DURING THIS TIME WITH A PERIOD OF 10 OR 11 SECONDS.
SEAS WILL SUBSIDE LATER IN THE WEEK.
15
FIRE WEATHER
EASTERLY OFFSHORE FLOW WILL CONTINUE TO INCREASE
THIS MORNING, PEAKING IN THE LATE MORNING AND GRADUALLY DECREASE
THROUGHOUT THE AFTERNOON AND EVENING. WIDESPREAD GUSTS UP TO 35 TO
45 MPH ARE LIKELY, WITH PEAK GUSTS REACHING 50 MPH OR MORE ALONG
RIDGELINES AND THROUGH THE CASCADE GAPS. WHILE RELATIVELY
HUMIDITIES WILL BE MARGINAL IN THE 25% TO 35% RANGE, GUSTY
EASTERLY GAP WINDS ACROSS THE CENTRAL CASCADES AND FOOTHILLS WILL
BRING IN WARMER AND DRIER AIR, WHICH MAY LEAD TO A QUICK AND LARGE
REDUCTION IN RH. THIS WILL LEAD TO CRITICAL FIRE WEATHER
CONDITIONS ACROSS THE CENTRAL CASCADES AND FOOTHILLS, AND A RED
FLAG WARNING REMAINS IN EFFECT FOR THESE AREAS THROUGH THIS
EVENING.
EASTERLY WINDS WILL EASE BY THE LATE EVENING TONIGHT, AND ONSHORE
FLOW WILL RESUME BY WEDNESDAY MORNING PROVIDING OVERNIGHT RH
RECOVERIES. MUCH COOLER AIR WILL MOVE INTO THE REGION, ALLOWING
THE REGION TO MOISTEN AND LEADING TO MUCH HIGHER MINIMUM RELATIVE
HUMIDITY VALUES. ONSHORE FLOW WILL CONTINUE THROUGH THE REMAINDER
OF THE WEEK, WITH CHANCES FOR WIDESPREAD WETTING RAINS AS SOON AS
SATURDAY AFTERNOON.
15
CLIMATE
WHILE NOT A RECORD HIGH TODAY (RECORD 91 DEGREES SET
IN 1967), THE FORECAST HIGH OF 85 DEGREES IN SEATTLE WOULD BE THE
SECOND WARMEST SEPTEMBER 16TH SINCE RECORDS STARTED AT SEATTLE
TACOMA AIRPORT IN 1945. 85 DEGREE PLUS DAYS ARE SOMEWHAT RARE THIS
TIME OF YEAR WITH ONLY 22 IN THE BOOKS IN THE LAST 80 YEARS FOR
THE LAST HALF OF SEPTEMBER AND OCTOBER (20 IN THE LAST HALF OF
SEPTEMBER, 2 IN OCTOBER). IN THE LAST 15 YEARS THERE HAS ONLY
BEEN 2 DAYS AFTER SEPTEMBER 15TH 85 DEGREES OR WARMER IN SEATTLE,
OCTOBER 16TH, 2022 88 DEGREES (THE SECOND WARMEST OCTOBER DAY ON
RECORD IN SEATTLE) AND 86 DEGREES ON SEPTEMBER 28TH, 2017.
FELTON
SEW WATCHES/WARNINGS/ADVISORIES
WA...RED FLAG WARNING UNTIL 11 PM PDT THIS EVENING FOR BLACK HILLS
AND SOUTHWEST INTERIOR LOWLANDS-NORTHEAST PUGET SOUND
LOWLANDS GENERALLY BELOW 1500 FEET-SOUTHEAST PUGET SOUND
LOWLANDS GENERALLY BELOW 1500 FEET-WEST SLOPES OF THE
CENTRAL CASCADES GENERALLY ABOVE 1500 FEET-WEST SLOPES OF
THE NORTH CASCADES GENERALLY ABOVE 1500 FEET.
WIND ADVISORY UNTIL MIDNIGHT PDT TONIGHT FOR FOOTHILLS AND
VALLEYS OF CENTRAL KING COUNTY-FOOTHILLS AND VALLEYS OF
PIERCE AND SOUTHERN KING COUNTIES-FOOTHILLS AND VALLEYS OF
SNOHOMISH AND NORTHERN KING COUNTIES.
PZ...SMALL CRAFT ADVISORY FROM 6 AM TO 11 AM PDT THIS MORNING FOR
COASTAL WATERS FROM CAPE FLATTERY TO JAMES ISLAND OUT 10 NM-
WEST ENTRANCE U.S. WATERS STRAIT OF JUAN DE FUCA.
SMALL CRAFT ADVISORY UNTIL 2 PM PDT THIS AFTERNOON FOR COASTAL
WATERS FROM POINT GRENVILLE TO CAPE SHOALWATER 10 TO 60 NM-
COASTAL WATERS FROM POINT GRENVILLE TO CAPE SHOALWATER OUT
10 NM.
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