603
FXUS66 KSEW 122310
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
410 PM PDT TUE AUG 12 2025
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 /TODAY THROUGH THURSDAY NIGHT/
ONE LAST HOT DAY IN
THIS STRETCH IS UNDERWAY ACROSS WESTERN WASHINGTON THIS
AFTERNOONWITH TEMPERATURES CLIMBING WELL INTO THE UPPER 80S TO
LOWER 90S AT THIS HOUR. 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 /FRIDAY THROUGH MONDAY/
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 WILL 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
UPPER LEVEL RIDGE OFFSHORE RETROGRADING WESTWARD TODAY.
UPPER LEVEL MOVING BY TO THE NORTH TONIGHT INTO WEDNESDAY. MOSTLY
ZONAL FLOW ALOFT THROUGHOUT THE PERIOD.
VFR ALL AREAS THIS AFTERNOON WITH VIS RESTRICTIONS OBSERVED AT KSHN
AND ADJACENT TERMINALS DUE TO WILDFIRE SMOKE. TONIGHT, ONSHORE FLOW
WILL INCREASE AS MARINE STRATUS TRACKS INLAND OVERNIGHT INTO
WEDNESDAY MORNING. WITH THAT, MVFR TO IFR CIGS EXPECTED - CAN'T RULE
OUT OUT LOCALIZED LIFR ALONG THE COAST. ARRIVAL OF THE STRATUS HAS
TRENDED SLOWER, ARRIVING AROUND PUGET SOUND AROUND 13-15Z BUT AT THE
COAST A TOUCH EARLIER. ALL REMAINING STRATUS SHOULD LIFT TO VFR BY
18-21Z WEDNESDAY FOR THE INTERIOR BUT COULD LINGER ALONG THE COAST.
MORE STRATUS POSSIBLE OVERNIGHT.
KSEA...CLEAR SKIES - VFR THIS AFTERNOON AND TONIGHT. 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.
MCMILLIAN
MARINE
HIGH PRESSURE WILL REMAIN OVER THE COASTAL WATERS BEFORE
WEAKENING BY THURSDAY. A THERMALLY INDUCED SURFACE TROUGH OVER THE
INLAND WATERS IS STILL ON TRACK TO PROGRESS EAST OF THE CASCADES
THIS EVENING. A DECENT 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 AND AGAIN WEDNESDAY NIGHT.
MCMILLIAN
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.
AIR QUALITY ALERT UNTIL 9 AM PDT FRIDAY FOR FOOTHILLS OF THE
WESTERN AND SOUTHERN OLYMPIC PENINSULA-MIDDLE CHEHALIS
RIVER VALLEY-OLYMPIA AND SOUTHERN PUGET SOUND-OLYMPICS-
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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