967
FXUS66 KSEW 211542
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
842 AM PDT TUE OCT 21 2025
SYNOPSIS
A WEAK UPPER RIDGE WILL PRODUCE DRY CONDITIONS FOR
WESTERN WASHINGTON TODAY. A FRONTAL SYSTEM WILL REACH THE AREA
ON WEDNESDAY WITH LIGHT PRECIPITATION ACROSS THE AREA. A DEEP
UPPER TROUGH OVER THE GULF OF ALASKA WILL BRING A STRONGER
FRONTAL SYSTEM INTO THE REGION AT THE END OF THE WEEK WITH THE
POTENTIAL FOR SOME HEAVY RAINFALL. A TROUGH WILL THEN SETTLE
OVER THE AREA BY THE WEEKEND FOR COOLER TEMPERATURES ALONG WITH
PERIODS OF RAIN AND MOUNTAIN SNOW.
SHORT TERM /TODAY THROUGH THURSDAY/
PREDOMINANTLY DRY
CONDITIONS THIS MORNING, ALTHOUGH A FEW SHOWERS ARE AROUND
OFFSHORE AND NEAR BELLINGHAM. OTHERWISE, AREAS OF FOG CONTINUES
OLYMPIA SOUTHWARDS AND TOWARDS HOQUIAM AND BREMERTON.
VISIBILITIES WILL IMPROVE IN THESE AREAS INTO MIDDAY, WITH A
MIX OF CLOUDS AND SUNSHINE THIS AFTERNOON. NO MAJOR FORECAST
UPDATES THIS MORNING. PREVIOUS DISCUSSION BELOW.
A DECAYING FRONTAL BOUNDARY OVER THE COASTAL WATERS WILL
CONTINUE TO DISSIPATE THIS MORNING AS WEAK SHORTWAVE RIDGING
SLIDES ONSHORE. THE END RESULT WILL BE THE REGIONS ONLY
COMPLETELY DRY DAY OF THE WEEK. SURFACE GRADIENTS HAVE BECOME
RELATIVELY FLAT THIS MORNING AND, COMBINED WITH SOME OVERNIGHT
CLEARING, WILL BE CONDUCIVE TO THE FORMATION OF FOG AND LOW
CLOUDS. WE'LL SEE SOME SUNSHINE THIS AFTERNOON ONCE THIS CLEARS
AWAY WITH AFTERNOON TEMPERATURES CLIMBING TO A COUPLE DEGREES
EITHER SIDE OF 60 FOR MOST OF THE LOWLANDS. CLOUDS WILL START TO
INCREASE LATER TONIGHT AS THE FIRST OF A SERIES OF FRONTAL
SYSTEMS APPROACHES THE AREA.
THE FIRST FRONT WILL BE RELATIVELY WEAK AS IT SPREADS SOME
LIGHT PRECIP ONSHORE WEDNESDAY AFTERNOON INTO WEDNESDAY NIGHT.
AS HAS BEEN ADVERTISED FOR SOME TIME NOW, THIS WILL SET THE
STAGE FOR A STRONGER SYSTEM TO AFFECT THE REGION LATE THURSDAY
THROUGH THE UPCOMING WEEKEND. AN UPPER TROUGH OVER THE GULF OF
ALASKA WILL DEEPEN ON THURSDAY WITH A WARM FRONT LIFTING NORTH
OVER THE AREA LATE IN THE DAY.
LONG TERM /THURSDAY NIGHT THROUGH MONDAY/
THE PREVIOUSLY
MENTIONED WARM FRONT WILL DRIVE SNOW LEVELS UPWARD TO 6500 TO
7500 FEET AS PRECIPITATION INCREASES THURSDAY NIGHT. THERE'S
STILL A DECENT SPREAD IN THE ENSEMBLE QPF AMOUNTS, BUT CURRENT
QPF FORECASTS DROP 3 TO 4 INCHES IN A GOOD SWATH OF THE COAST
AND OLYMPICS AND A PORTION OF THE NORTH CASCADES IN THE 36 HOURS
FROM 00Z FRIDAY TO 12Z SATURDAY. THIS WILL PRODUCE SOME SHARP
RISES ON RIVERS, BUT RIVER FLOODING IS NOT EXPECTED. THE PRIMARY
IMPACTS WILL BE LOCALIZED URBAN AND SMALL STREAM FLOODING AS
WELL AS AREAS WITH POOR DRAINAGE. IN ADDITION, WINDY CONDITIONS
ARE EXPECTED COASTAL AREAS AND NORTH INTERIOR.
SNOW LEVELS WILL BEGIN TO FALL BEHIND A TRAILING COLD
FRONT FRIDAY AFTERNOON INTO FRIDAY NIGHT. THE FOCUS WILL LIKELY
TO SHIFT TO MOUNTAIN SNOW POTENTIAL BY THE SECOND HALF OF THE
WEEKEND. MODELS BRING ANOTHER DISTURBANCE EMBEDDED IN THE UPPER
TROUGH ONSHORE LATER SATURDAY INTO SATURDAY NIGHT. THIS WILL
PRODUCE ANOTHER ROUND OF PRECIP WITH 850 MILLIBAR TEMPERATURES
FALLING TO -2 OR -3 C BY SUNDAY MORNING WHICH SHOULD BRING SNOW
LEVELS DOWN TO MOST (IF NOT ALL) OF THE MOUNTAIN PASSES. IT'S A
BIT EARLY TO FOCUS ON AMOUNTS, BUT IT'S SOMETHING TO BE MINDFUL
OF IF YOUR WEEKEND PLANS INVOLVE TRAVEL THROUGH THE CASCADES.
UNSETTLED CONDITIONS WILL CONTINUE INTO EARLY NEXT WEEK AS THE
NORTHEAST PACIFIC REMAINS QUITE ACTIVE. 27
AVIATION
ZONAL FLOW ALOFT WILL WEAKEN AS A RIDGE AMPLIFIES TODAY
OVER THE REGION. CEILINGS EARLY THIS MORNING ARE MOSTLY VFR WITH
MOSTLY CLEAR SKIES. SOME LOW TO MID LEVEL CLOUDS PERSIST OVER
NORTHERN PORTIONS OF THE AREA FROM A DISSIPATING FRONT. FOG HAS
BEGUN TO DEVELOP IN THE VALLEYS OVER THE SOUTHERN HALF OF THE
REGION, HAVING REACHED HQM, OLM, AND PWT. EXPECT FOG AND LOW STRATUS
TO SLOWLY INCREASE IN COVERAGE THROUGH THE REST OF THE MORNING. THE
TERMINALS WITH THE BEST CHANCES FOR FOG/STRATUS WILL BE BLI AND PAE,
BUT ALL AREA TERMINALS WILL HAVE THE RISK TO SEE AT LEAST A BRIEF
PERIOD OF LOW CIGS/VIS THIS MORNING. CONDITIONS SHOULD BEGIN TO
IMPROVE AROUND 18-20Z. ONCE FOG CLEARS, MOSTLY CLEAR SKIES WILL KEEP
VFR CONDITIONS THROUGH THE REST OF TODAY AND MUCH OF TONIGHT. MOSTLY
CLEAR SKIES AND LIGHT WINDS WILL ALLOW FOR THE POTENTIAL FOR FOG
POTENTIAL, IN PARTICULAR, ACROSS THE SOUTHWEST INTERIOR.
WINDS, MOSTLY LIGHT AND VARIABLE TO S/SE THIS MORNING, WILL SWITCH
OVER TO N/NE BUT STILL REMAIN PRETTY LIGHT, AROUND 5 KT OR LESS.
MOSTLY LIGHT WINDS TONIGHT EXPECT THROUGH THE STRAIT AND THE
CHEHALIS GAP (HQM) WITH SLIGHTLY ENHANCED OFFSHORE FLOW
OVERNIGHT.
KSEA...VFR CONDITIONS EARLY THIS MORNING WITH MOSTLY CLEAR SKIES.
FOG/LOW STRATUS HAS BEEN A LITTLE SLOW TO GET GOING, SO WILL
SLIGHTLY DELAY THE ONSET, BUT THE POTENTIAL IS NOT YET ELIMINATED
THIS MORNING. VFR CONDITIONS RETURN ONCE FOG/STRATUS CLEARS, BETWEEN
AROUND 18-20Z. MOSTLY CLEAR SKIES (VFR) THROUGH THE REST OF TODAY
INTO TONIGHT. FOG POTENTIAL FOR WEDNESDAY MORNING LOOKS MORE FOCUSED
SOUTH AND WEST OF THE TERMINAL AS OFFSHORE DEVELOPS OVERNIGHT
TOMORROW. SE WINDS WILL SHIFT TO N/NE AFTER AROUND 18Z THIS MORNING,
SLOWLY BECOMING MORE E OVERNIGHT. SPEEDS REMAIN RELATIVELY LIGHT,
AROUND 4-6 KT.
62
MARINE
A DISSIPATING FRONT IS CURRENTLY MOVING THROUGH THE
COASTAL WATERS THIS MORNING, NOT BRINGING MUCH IN THE WAY WIND
ACROSS THE AREA THIS MORNING. BROAD HIGH PRESSURE WILL KEEP WINDS
WEAK UNTIL WEDNESDAY WHEN A FRONTAL SYSTEM WILL MOVE THROUGH THE
AREA. THIS FRONT WILL ALLOW FOR WINDS TO INCREASE, THROUGH THEY LOOK
TO REMAIN JUST BELOW ADVISORY CRITERIA. THERE MAY BE SOME ISOLATED
SMALL CRAFT ADVISORY WINDS NEAR THE COAST WHERE THE TERRAIN HAS MORE
INFLUENCE, BUT THAT LOOKS TO BE ISOLATED AND ONLY FOR A SHORT TIME
AS THE FRONT MOVES THROUGH WEDNESDAY AFTERNOON.
THE MORE IMPACTFUL SYSTEM WILL APPROACH THE AREA ON THURSDAY.
WINDS WILL BEGIN TO INCREASE THURSDAY MORNING AND PEAK AS THE FRONT
MOVES THROUGH THURSDAY NIGHT INTO EARLY FRIDAY MORNING.
WINDS WILL MOST LIKELY REACH GALE FORCE ACROSS THE COASTAL WATERS,
AS WELL AS THROUGH THE EAST STRAIT OF JUAN DE FUCA AND INTO THE
NORTHERN INLAND WATERS. WIND GUSTS COULD REACH AS HIGH AS 50 KT IN
THE EAST STRAIT.
WINDS WILL EASE ON FRIDAY, THOUGH ANOTHER SYSTEM LOOKS TO BE RIGHT
ON ITS HEELS, MOVING THROUGH THE COASTAL WATERS SATURDAY.
THERE IS UNCERTAINTY WITH THE EXACT TRACK OF THIS LOW, BUT CURRENTLY
THE STRONGEST WINDS LOOK TO BE FARTHER SOUTH INTO THE OREGON WATERS.
THE ACTIVE PATTERN LOOKS TO CONTINUE INTO EARLY NEXT WEEK WITH
ELEVATED WINDS AND SEAS PERSISTING THROUGH THEN.
SEAS AROUND 8 TO 10 FT EARLY THIS MORNING WILL INCREASE SHARPLY THIS
MORNING AS LONG PERIOD SWELL ARRIVES AT THE COASTAL WATERS.
SEAS LOOK TO PEAK IN THE 15-17 FT RANGE THIS AFTERNOON WITH A
DOMINANT PERIOD OF AROUND 16 SECONDS. SEAS WILL EASE OVERNIGHT BACK
TO AROUND 8-10 FT BY WEDNESDAY MORNING, BUT WILL BEGIN TO RISE AGAIN
EARLY THURSDAY. SEAS WILL PEAK THURSDAY NIGHT INTO FRIDAY AS THE
FRONT MOVES THROUGH, UP TO AROUND 18-20 FT, WITH A MIX OF SOUTHERLY
AND WESTERLY COMPONENTS. SEAS WILL EASE A BIT ON FRIDAY, BUT REMAIN
IN THE 12-16 FT RANGE THROUGH THE WEEKEND INTO EARLY NEXT WEEK.
62
HYDROLOGY
A FRONTAL SYSTEM THAT WILL TAP INTO SOME SUBTROPICAL
MOISTURE WILL MOVE ACROSS WESTERN WASHINGTON LATE THURSDAY THROUGH
FRIDAY. RAINFALL AMOUNTS ARE FORECAST TO BE HEAVIEST OVER THE
OLYMPIC PENINSULA, WITH THE LATEST FORECAST SHOWING 2 TO 4 INCHES OF
PRECIPITATION OVER THE OLYMPICS THURSDAY EVENING THROUGH FRIDAY
AFTERNOON. RAINFALL AMOUNTS ARE EXPECTED TO BE LESS FOR THE
CASCADES, RANGING 1 TO 3 INCHES THROUGH FRIDAY EVENING. ALTHOUGH
PRECIPITATION IS EXPECTED TO CONTINUE AT TIMES SATURDAY INTO EARLY
NEXT WEEK, SNOW LEVELS WILL LOWER TO 3000 TO 4000 FEET BY LATER IN
THE WEEKEND. AT THIS TIME, CURRENT FORECASTS BRING THE SKOKOMISH
RIVER NEAR ACTION STAGE LATE FRIDAY. MODERATE TO HEAVY RAIN FRIDAY
MAY ALSO LEAD TO ROADWAY PONDING AND MINOR NUISANCE FLOODING OF POOR
DRAINAGE AREAS.
JD
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...SMALL CRAFT ADVISORY UNTIL 5 AM PDT WEDNESDAY FOR COASTAL
WATERS FROM CAPE FLATTERY TO JAMES ISLAND 10 TO 60 NM-
COASTAL WATERS FROM CAPE FLATTERY TO JAMES ISLAND OUT 10
NM-COASTAL WATERS FROM JAMES ISLAND TO POINT GRENVILLE 10
TO 60 NM-COASTAL WATERS FROM JAMES ISLAND TO POINT
GRENVILLE OUT 10 NM-COASTAL WATERS FROM POINT GRENVILLE
TO CAPE SHOALWATER 10 TO 60 NM-COASTAL WATERS FROM POINT
GRENVILLE TO CAPE SHOALWATER OUT 10 NM-GRAYS HARBOR BAR-
WEST ENTRANCE U.S. WATERS STRAIT OF JUAN DE FUCA.
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