483
FXUS66 KSEW 130317
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
817 PM PDT TUE AUG 12 2025
UPDATE
LATEST SATELLITE IMAGERY SHOWS MOSTLY CLEAR SKIES ACROSS
MOST OF WESTERN WASHINGTON THIS EVENING, ALTHOUGH SOME LOCATIONS
LIKE PUGET SOUND AND WESTERN WHATCOM COUNTY ARE SEEING HAZY SKIES
DUE TO WILDFIRE SMOKE. TEMPERATURES ARE STILL QUITE WARM THIS
EVENING IN THE INTERIOR LOWLANDS, WITH TEMPERATURES IN THE MID TO
UPPER 80S. NO SIGNIFICANT UPDATES TO THE FORECAST THIS EVENING.
REFER TO AN UPDATED AVIATION AND MARINE SECTION BELOW. 29
SYNOPSIS
ONE LAST HOT AND DRY DAY ACROSS THE REGION TODAY,
WITH WIDESPREAD MODERATE HEATRISK. A PASSING DISTURBANCE TO THE
NORTH WILL BRING COOLER AND CLOUDIER CONDITIONS TO THE REGION
WEDNESDAY. INCREASING CHANCES OF WIDESPREAD RAIN ACROSS THE
REGION FRIDAY AND SATURDAY AS A STRONGER WEATHER SYSTEM MOVES
ACROSS THE AREA. LINGERING SHOWERS WILL TAPER ON SUNDAY FOR A
DRIER START TO NEXT WEEK.
SHORT TERM /TONIGHT THROUGH FRIDAY/
ONE LAST HOT DAY IN
THIS STRETCH IS UNDERWAY ACROSS WESTERN WASHINGTON THIS
AFTERNOON WITH TEMPERATURES CLIMBING WELL INTO THE UPPER 80S TO
LOWER 90S. MEANWHILE, ONSHORE FLOW HAS MAINTAINED NOTABLY COOLER
TEMPERATURES ALONG THE COASTLINE.
THE UPPER LEVEL RIDGE WILL BREAK DOWN TONIGHT AS A PASSING
DISTURBANCE APPROACHES INTO SOUTHERN B.C. TOMORROW. THIS WILL
BRING A STRONGER PUSH OF ONSHORE FLOW WEDNESDAY, USHERING
IN COOLER AND CLOUDIER CONDITIONS ACROSS THE REGION. HOWEVER,
WITH THE SWITCH OF WIND DIRECTION, EXPECT THAT SOME HAZE AND
SMOKE FROM A LARGE FIRE BURNING ON VANCOUVER ISLAND MAY BEGIN TO
MOVE EASTWARD ACROSS THE LOCAL AREA. THIS MAY BE MOST PROMINENT
ACROSS THE NORTHERN PORTION OF THE AREA (THE SAN JUAN ISLANDS
EAST INTO THE NORTH CASCADES), BUT ANOTHER SOURCE WILL BE THE
BEAR GULCH FIRES. CONSULT THE LATEST FORECAST FROM THE LOCAL
CLEAN AIR AGENCIES FOR THE LATEST AIR QUALITY INFORMATION.
CONDITIONS WILL REMAIN COOLER AND CLOUDIER INTO THURSDAY AS AN
UPPER TROUGH BECOMES WELL ESTABLISHED OVER THE REGION. CHANCES
OF RAIN WILL INCREASE THROUGHOUT THE DAY ALONG THE COAST AS A
FRONTAL SYSTEM APPROACHES THE REGION. RAIN CHANCES WILL THEN
START TO MOVE INLAND BY LATE THURSDAY NIGHT.
LONG TERM /SATURDAY THROUGH TUESDAY/
ATTENTION THEN TURNS TO THE
WEEKEND WITH AN UNSEASONABLY STRONG COLD FRONT THEN POSITIONED
TO MOVE INTO THE REGION FRIDAY AND SATURDAY. THIS WILL (>80
PERCENT CHANCE) BRING A WIDESPREAD WETTING RAIN TO THE REGION
FOR THE START OF THE WEEKEND. THIS WILL LIKELY BE A BENEFICIAL
DOSE OF RAIN FOR MUCH OF THE AREA, PARTICULARLY ONGOING FIRES,
WITH THE MOST LIKELY AMOUNTS NEAR AN INCH IN THE LOWLANDS
(HIGHER AT THE COAST) AND AROUND 2 INCHES OR MORE IN THE
MOUNTAINS. IT'S WORTH NOTING THAT THE ENSEMBLE GUIDANCE
GENERALLY FITS WITHIN TWO CLUSTERS OF SOLUTIONS - 1) A SHARPER
SHORTWAVE TROUGH THAT FOCUSES HIGHER RAINFALL AMOUNTS IN THE
NORTHERN PORTIONS OF THE AREA (WITH AMOUNTS CLOSER TO THE 90TH
PERCENTILE) AND 2) A MORE BROAD DISTURBANCE THAT BRINGS THE
HEAVIEST RAINFALL MORE EVENLY POSITIONED OVER WESTERN WASHINGTON
BUT WITH THE RAINFALL AMOUNTS CLOSER TO THE 50TH PERCENTILE. AS
A RESULT, WHILE THERE'S SOME UNCERTAINTY IN JUST HOW WET IT MAY
BE, IT'S LIKELY GOING TO BE A COOL AND WET COUPLE OF DAYS
(ESPECIALLY BY MID-AUGUST STANDARDS). THOSE WITH RECREATION PLANS
NEAR AREA RIVERS SHOULD PAY PARTICULAR ATTENTION AS THESE
RAINFALL AMOUNTS (ESPECIALLY SOME OF THE HIGHER-END SCENARIOS)
WOULD CAUSE FAIRLY SIGNIFICANT RISES ON MANY AREA RIVERS.
ADDITIONALLY, EXPECT TO A NOTABLY COOLER AIR MASS ARRIVE AND DROP
SNOW LEVELS DOWN TO AROUND 8500 FT INTO SUNDAY. THIS COULD BRING A
FEW LIGHT SNOW SHOWERS OVER THE MOUNTAINS WITH SOME ACCUMULATIONS
ON THE HIGHEST PEAKS. AGAIN, THOSE HEADING TO THE MOUNTAINS
SHOULD CLOSELY MONITOR THE FORECAST AND PREPARE FOR THIS
SIGNIFICANT SHIFT IN THE WEATHER PATTERN THIS WEEKEND. IN THE
LOWLANDS, TEMPERATURES MAY ONLY TOP OUT IN THE 60S ON FRIDAY AND
AROUND 70 ON SATURDAY, SIGNIFICANTLY COOLER THAN OUR 90 DEGREE
READINGS TO START THE WEEK. CULLEN
AVIATION
WEST-NORTHWESTERLY FLOW, BECOMING ZONAL AT TIMES,
EXPECTED TONIGHT INTO WEDNESDAY AS AN UPPER LEVEL TROUGH IN CANADA
SHIFTS EASTWARD. SURFACE WINDS MOSTLY NORTHERLY, WITH SOME WAGGLE TO
EITHER THE NORTHEAST OR NORTHWEST DEPENDING ON LOCATION AND TERRAIN.
EXCEPTION IS HQM, WHERE SW WINDS HAVE SET UP, WITH REMAINING
TERMINALS EXPECTED TO FOLLOW SUIT OVERNIGHT TONIGHT. SPEEDS
GENERALLY 4-8 KTS WITH HQM ONCE AGAIN BEING ODD SITE OUT WITH SPEEDS
10-15 KTS. ALL SITES EXPECTED TO RANGE 4-8 KTS OVERNIGHT BEFORE
RAMPING UP TO 8-12 KTS IN THE LATE MORNING/EARLY AFTERNOON WITH SOME
SITES SEEING GUSTS UP TO 20 KTS.
VFR CONDITIONS THROUGHOUT THE CWA THIS EVENING. NORTHERN MASON
COUNTY MERITS SPECIAL MENTION AS SMOKE FROM WILDFIRES THERE COULD
RESULT IN LOCALIZED DIMINISHED CONDITIONS. OTHERWISE, SMOKE ISSUES
REMAIN GENERALLY ALOFT, EITHER FROM THE AFOREMENTIONED MASON COUNTY
ACTIVITY OR, POTENTIALLY IMPACTING BLI, FROM CANADIAN WILDFIRES.
MARINE PUSH OVERNIGHT WILL BRING LOW-LEVEL STRATUS THROUGHOUT THE
AREA BY EARLY WEDNESDAY MORNING WITH MOST LOCATIONS SEEING MVFR TO
IFR CONDITIONS BY 12Z...WITH WESTERN TERMINALS LIKELY SEEING THESE
CONDITIONS EARLIER. AS PER TYPICAL PATTERN, CONDITIONS EXPECTED TO
IMPROVE TO WIDESPREAD VFR CONDITIONS EARLY WEDNESDAY AFTERNOON,
EXCEPT FOR ALONG THE COAST WHERE IMPROVEMENT MAY ONLY GET TO MVFR.
WHILE CIGS LIFT, MODELS CONTINUE TO SUGGEST THAT BKN-OVC CONDITIONS
WILL PERSIST THROUGHOUT THE REMAINDER OF THE TAF PERIOD.
KSEA...VFR CONDITIONS TONIGHT WITH SOME SMOKE ALOFT. STRATUS
REACHING THE TERMINAL 12Z-15Z WEDNESDAY MORNING. HREF IS INDICATING
A 50% OF CIGS BELOW 3K FT WITH A 20-30% CHANCE OF CIGS BELOW 1K FT.
CLOUDS SHOULD LIFT TO VFR BY 18-19Z WEDNESDAY. NW WINDS TURNING MORE
SW TOMORROW MORNING 5-10 KT WITH GUSTS POSSIBLE IN THE AFTERNOON.
18/MCMILLIAN
MARINE
HIGH PRESSURE WILL REMAIN OVER THE COASTAL WATERS BEFORE
WEAKENING BY THURSDAY. AN IMPRESSIVE FRONT FOR THIS TIME OF THE YEAR
WILL REACH THE COASTAL WATERS FRIDAY AND MOVE INLAND SATURDAY.
SMALL CRAFT ADVISORY OUTER COASTAL WATERS THROUGH WEDNESDAY NIGHT
FOR SEAS 10 OR 11 FEET WITH A 10 SECOND PERIOD AND NORTHERLY WINDS
OCCASIONALLY 20 TO 25 KNOTS TONIGHT AND WEDNESDAY. SEAS SUBSIDING
WEDNESDAY NIGHT BUT WILL REMAIN CHOPPY AT 8 FEET WITH AN 8 SECOND
PERIOD. SMALL CRAFT ADVISORY WESTERLIES CENTRAL AND EASTERN STRAIT
OF JUAN DE FUCA TONIGHT WITH HEADLINE IN PLACE. THESE WINDS WILL BE
POSSIBLE AGAIN WEDNESDAY NIGHT, SO ANOTHER HEADLINE MIGHT BE NEEDED.
MCMILLIAN/18
FIRE WEATHER
ELEVATED FIRE WEATHER CONDITIONS WILL COME TO AN END
OVERNIGHT AS AN APPROACHING TROUGH LEADS TO INCREASING ONSHORE FLOW.
THIS WILL RESULT IN A STEEP DROP IN TEMPERATURES ON WEDNESDAY ALONG
WITH GOOD RELATIVE HUMIDITY RECOVERIES. CHANCES FOR RAINFALL THEN
INCREASE TOWARDS THE END OF THE WEEK. THERE IS A HIGH DEGREE OF
CONFIDENCE THAT A FRONTAL SYSTEM WILL PRODUCE WETTING RAINS ACROSS
THE ENTIRETY OF THE REGION FRIDAY INTO EARLY SATURDAY. 27
SEW WATCHES/WARNINGS/ADVISORIES
WA...HEAT ADVISORY UNTIL 10 PM PDT THIS EVENING FOR CITY OF SEATTLE-
DOWNTOWN EVERETT / MARYSVILLE AREA-EASTERN KITSAP COUNTY-
EASTERN STRAIT OF JUAN DE FUCA-EASTSIDE-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-FOOTHILLS AND VALLEYS
OF THURSTON AND LEWIS COUNTIES-FOOTHILLS AND VALLEYS OF THE
NORTH CASCADES-FOOTHILLS OF THE WESTERN AND SOUTHERN
OLYMPIC PENINSULA-LAKE CRESCENT AREA INCLUDING US 101-LOWER
CHEHALIS RIVER VALLEY-LOWLANDS OF LEWIS AND SOUTHERN
THURSTON COUNTIES-LOWLANDS OF PIERCE AND SOUTHERN KING
COUNTIES-LOWLANDS OF WESTERN SKAGIT AND NORTHWESTERN
SNOHOMISH COUNTIES-LOWLANDS OF WESTERN WHATCOM COUNTY-
MIDDLE CHEHALIS RIVER VALLEY-NORTHERN HOOD CANAL-OLYMPIA
AND SOUTHERN PUGET SOUND-SHORELINE / LYNNWOOD / SOUTH
EVERETT AREA-SOUTHERN HOOD CANAL-WILLAPA AND BLACK HILLS.
PZ...SMALL CRAFT ADVISORY UNTIL 5 AM PDT WEDNESDAY FOR CENTRAL U.S.
WATERS STRAIT OF JUAN DE FUCA-EAST ENTRANCE U.S. WATERS
STRAIT OF JUAN DE FUCA.
SMALL CRAFT ADVISORY UNTIL 11 PM PDT THIS EVENING FOR COASTAL
WATERS FROM JAMES ISLAND TO POINT GRENVILLE OUT 10 NM-
COASTAL WATERS FROM POINT GRENVILLE TO CAPE SHOALWATER OUT
10 NM.
SMALL CRAFT ADVISORY UNTIL 6 AM PDT THURSDAY 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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