955
FXUS66 KSEW 201804
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
1004 AM PST SAT DEC 20 2025
UPDATE
NO CHANGES MADE TO THE INHERITED FORECAST. CURRENT
TEMPERATURES RANGE BETWEEN THE UPPER 30S TO LOWER 40S ACROSS W
WA. LOWLAND RAIN SHOWERS AND MOUNTAIN SNOW ARE STILL ON TRACK TO
CONTINUE TODAY AS A WINTER STORM WARNING REMAINS IN EFFECT UNTIL
THIS AFTERNOON. THE PREVIOUS DISCUSSION IS BELOW ALONG WITH AN
UPDATED AVIATION AND HYDROLOGY SECTION:
SYNOPSIS
PERIODS OF LOWLAND RAIN, MOUNTAIN SNOW, AND BREEZY CONDITIONS
WILL CONTINUE ACROSS WESTERN WASHINGTON OVER THE NEXT WEEK AS A
SERIES OF WEATHER SYSTEMS MOVES ACROSS THE REGION. A TREND
TOWARDS COOLER CONDITIONS LOOKS LIKELY AROUND MIDWEEK.
SHORT TERM /TODAY THROUGH MONDAY/
A BROAD UPPER LEVEL TROUGH OVER THE GULF OF ALASKA WILL CONTINUE
TO STEER SHORTWAVES ACROSS THE REGION THROUGH THE WEEKEND. THIS
WILL MAINTAIN UNSETTLED AND SHOWERY CONDITIONS ACROSS WESTERN
WASHINGTON, WITH THE LATEST RADAR SHOWING SHOWERS CONTINUING TO
STREAM ACROSS THE AREA EARLY THIS MORNING. SNOW WILL CONTINUE
FOR THE MOUNTAINS, WITH SNOW LEVELS GENERALLY EXPECTED TO
REMAIN BETWEEN 1500-3000 FT THROUGH THE WEEKEND. A WINTER STORM
WARNING REMAINS IN EFFECT FOR THE CASCADES, WHERE ROUGHLY
ANOTHER 1-2 FT IS EXPECTED TO FALL AT SNOQUALMIE AND STEVENS
PASSES THROUGH THIS AFTERNOON. SNOW WILL BE HEAVY AT TIMES,
ESPECIALLY DURING THE LATE MORNING AND AFTERNOON HOURS, SO USE
CAUTION IF YOU'RE PLANNING TO TRAVEL ACROSS THE CASCADES. IN
ADDITION TO SNOW, A SLIGHT CHANCE OF ISOLATED THUNDERSTORMS WILL
REMAIN POSSIBLE FOR AREAS PRIMARILY ALONG THE PACIFIC COAST
BOTH TODAY AND AGAIN ON SUNDAY. OVERALL RAINFALL AMOUNTS FOR THE
LOWLANDS THROUGH SUNDAY NIGHT ARE STILL EXPECTED TO BE WITHIN
0.50-1.50 INCHES AS A WHOLE, THOUGH SOME AREAS ACROSS THE
CENTRAL SOUND AND NORTHEASTERN OLYMPIC PENINSULA WILL LIKELY
SEE SOME LOWER AMOUNTS DUE TO RAIN SHADOWING. SOUTHERLY WINDS
WILL BE BREEZY AT TIMES THROUGH THE DAY SATURDAY AND AGAIN ON
SUNDAY, WITH WINDS GENERALLY EXPECTED TO PERSIST BETWEEN 25-30
MPH.
A STRONGER SYSTEM WILL THEN MOVE INTO THE AREA ON MONDAY AND
WILL BRING ANOTHER ROUND OF GUSTY WINDS, LOWLAND RAIN, AND
MOUNTAIN SNOW TO THE AREA. SOUTHERLY WINDS WILL PICK UP DURING
THE MORNING HOURS AND WILL PEAK IN THE AFTERNOON AT 30-35 MPH,
BEFORE DECREASING AGAIN BY LATE MONDAY. ANOTHER 9-12 INCHES OF
SNOW WILL BE POSSIBLE FOR THE MOUNTAIN PASSES, WITH LOCALLY
HIGHER TOTALS EXPECTED FOR HIGHER ELEVATIONS. RAINFALL AMOUNTS
OF 0.25-1.0 INCH ARE EXPECTED FOR THE LOWLANDS.
LONG TERM /MONDAY NIGHT THROUGH FRIDAY/
CONDITIONS LOOK TO REMAIN RATHER ACTIVE THROUGH MUCH OF THE NEXT
WEEK AS ENSEMBLES REMAIN IN PRETTY GOOD AGREEMENT WITH THE
UPPER LEVEL TROUGH DIGGING ACROSS THE NORTHEASTERN PACIFIC AND
SWINGING ADDITIONAL DISTURBANCES INTO THE REGION. THIS WOULD
CONTINUE TO BRING PERIODS OF LOWLAND RAIN, MOUNTAIN SNOW, AND
BREEZY WINDS TO WESTERN WASHINGTON THROUGH MUCH OF THE NEXT
WEEK. THE WEATHER PATTERN WILL ALSO ALLOW FOR A TREND TOWARDS
COOLER TEMPERATURES, ESPECIALLY DURING THE OVERNIGHT PERIOD,
WHERE WE MAY START TO SEE MORNING LOWS APPROACH FREEZING IN SOME
SPOTS BY MIDWEEK.
14
AVIATION
ZONAL FLOW ALOFT WILL PERSIST THROUGHOUT THE DAY TODAY
BEFORE SHIFTING MORE SOUTHWESTERLY BY SUNDAY MORNING. SURFACE WINDS
OVER W WA THIS MORNING ARE SOUTH TO SOUTHWESTERLY WITH SPEEDS
GENERALLY 5-15 KT WITH GUSTS TO 20 KT.
CIGS LARGELY MVFR FOR MUCH OF THE AREA. WITH ANOTHER ROUND OF
SHOWERS EXPECTED TO MOVE INTO THE AREA LATE THIS MORNING/EARLY
THIS AFTERNOON, ANY IMPROVEMENT TO CIGS WILL BE LIMITED, IF
EXISTENT AT ALL. LATEST FORECASTS SUGGEST THAT THIS ACTIVITY
WILL LIKELY PULL CIGS A LITTLE BIT LOWER WITH SOME LOCATIONS
DIPPING INTO LOW-END MVFR. ISOLATED SPOTS OF IFR WILL STILL BE
POSSIBLE, ESPECIALLY THOSE TERMINALS MORE PRONE TO LOWER CIGS.
KSEA...MVFR CONDITIONS IN PLACE AS THE NEXT WAVE OF SHOWERS
MOVES INTO THE AREA. SURFACE WINDS TO REMAIN ELEVATED,
GENERALLY 8-12 KTS...BUT NOT SO CONFIDENT IN THE PRESENCE OF
GUSTS. THEY MAY BE ISOLATED IN NATURE, BUT NOT SURE IF THEY
WARRANT INCLUSION INTO THE DOMINANT WEATHER FEATURES.
33/18
MARINE
WINDS WILL BE BREEZY ACROSS PORTIONS OF THE COASTAL WATERS,
PUGET SOUND, ADMIRALTY INLET, AND THE NORTHERN INLAND WATERS
TODAY, WITH HI-RES PROBABILITIES SHOWING ROUGHLY A 70-90
PERCENT CHANCE OF WINDS EXCEEDING 21 KT ACROSS THESE SPOTS BY
LATE MORNING. A SLIGHT CHANCE OF THUNDERSTORMS WILL ALSO REMAIN
POSSIBLE AGAIN THIS AFTERNOON AND EVENING, WITH THE HIGHEST
CHANCES REMAINING CONFINED TO THE PACIFIC COAST AND ACROSS THE
WESTERN STRAIT OF JUAN DE FUCA. GUSTY WINDS, BRIEF HEAVY
DOWNPOURS, REDUCTIONS IN VISIBILITY, AND LIGHTNING WILL BE
POSSIBLE IN ANY STORMS THAT DO DEVELOP ACROSS THE WATERS.
A WEAKENING FRONTAL SYSTEM WILL THEN MOVE INTO THE WATERS ON
SUNDAY, BRINGING ANOTHER ROUND OF BREEZY SOUTHERLY WINDS TO THE
AREA. A STRONGER SYSTEM IS THEN SET TO MOVE INTO THE AREA
WATERS ON MONDAY. OVERALL, EXPECT AN ACTIVE PATTERN TO CONTINUE
ACROSS THE AREA WATERS THROUGHOUT THE WEEK, WITH ADDITIONAL
ROUNDS OF ELEVATED WINDS AND SEAS AND HEADLINES LIKELY.
SEAS CONTINUE TO HOVER BETWEEN 10-12 FT EARLY THIS MORNING AND
WILL GRADUALLY SUBSIDE TOWARDS 8-10 FT BY THIS EVENING. SEAS
ARE EXPECTED TO RISE AGAIN BY LATE MONDAY, APPROACHING 12-14 FT
AGAIN ACROSS THE COASTAL WATERS.
14
HYDROLOGY
ALTHOUGH SHOWERS ARE EXPECTED OVER W WA FOR MUCH
OF THE DAY TODAY, PRECIP AMOUNTS SHOULD NOT INTERFERE WITH THE
OVERALL DOWNWARD TREND BEING SEEN ON MOST AREA RIVERS. RIVERS
WITH DAM REGULATED FLOWS EXPECTED TO REMAIN NEAR OR JUST OVER
FLOOD LEVELS FOR THE TIME BEING AS THE PROCESS OF ELIMINATING
EXCESS WATER FROM PREVIOUS ATMOSPHERIC RIVERS CONTINUE.
AS FOR RIVERS THAT ARE STILL IN FLOOD WITHOUT DAM REGULATION:
* THE CHEHALIS RIVER AT PORTER WILL HOVER NEAR MINOR FLOOD STAGE FOR
THE NEXT FEW DAYS BEFORE RECEDING, WHILE THE UPSTREAM GAUGE AT
GRAND MOUND HAS CRESTED BELOW FLOOD STAGE AND WILL SEE RIVER
LEVELS RECEDE GRADUALLY OVER THE NEXT COUPLE OF DAYS.
* THE SKOKOMISH RIVER AT POTLATCH ALSO SEES RIVER LEVELS
GRADUALLY EASING WHILE REMAINING IN MINOR FLOOD STAGE.
HOWEVER, ADDITIONAL RISES ARE EXPECTED IN THE RIVER FOR THE
START OF NEXT WEEK...KEEPING THE WATERS NEAR MODERATE FLOOD
STAGE.
WITH THE VARIANCES BASED ON NEEDS ASSOCIATED WITH DAMS AND REGULATED
RIVERS, FLOWS MAY INCREASE OR DECREASE BELOW FORECAST LEVELS
RAPIDLY. THAT SAID, RIVERS THAT REMAIN RIGHT AROUND FLOOD STAGE,
EVEN THOSE THAT LINGER JUST BELOW, WILL LIKELY RETAIN THEIR
HEADLINES IN CASE THE SITUATION CHANGES.
THE LATEST WAVE OF SHOWERS WILL CONTINUE TO FALL ON ALREADY
SATURATED GROUND AND AS SUCH, THE LANDSLIDE THREAT WILL REMAIN HIGH
THROUGH THE WEEKEND.
SEW WATCHES/WARNINGS/ADVISORIES
WA...WINTER STORM WARNING UNTIL 4 PM PST THIS AFTERNOON FOR
CASCADES OF PIERCE AND LEWIS COUNTIES-CASCADES OF
SNOHOMISH AND NORTHERN KING COUNTIES-CASCADES OF SOUTHERN
KING COUNTY-CASCADES OF WHATCOM AND SKAGIT COUNTIES.
FLOOD WATCH UNTIL 10 AM PST THIS MORNING FOR CASCADES OF
PIERCE AND LEWIS COUNTIES-CASCADES OF SNOHOMISH AND
NORTHERN KING COUNTIES-CASCADES OF SOUTHERN KING COUNTY-
CITY OF SEATTLE-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-LOWLANDS OF LEWIS AND SOUTHERN
THURSTON COUNTIES-LOWLANDS OF PIERCE AND SOUTHERN KING
COUNTIES-SHORELINE / LYNNWOOD / SOUTH EVERETT AREA-
WILLAPA AND BLACK HILLS.
PZ...SMALL CRAFT ADVISORY UNTIL 4 PM PST THIS AFTERNOON 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.
SMALL CRAFT ADVISORY UNTIL 10 AM PST THIS MORNING FOR CENTRAL
U.S. WATERS STRAIT OF JUAN DE FUCA-WEST ENTRANCE U.S.
WATERS STRAIT OF JUAN DE FUCA.
SMALL CRAFT ADVISORY UNTIL 4 AM PST SUNDAY FOR ADMIRALTY INLET-
NORTHERN INLAND WATERS INCLUDING THE SAN JUAN ISLANDS.
SMALL CRAFT ADVISORY UNTIL 10 PM PST THIS EVENING FOR PUGET
SOUND AND HOOD CANAL.
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page