398
FXUS66 KSEW 211659
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
859 AM PST SUN DEC 21 2025
UPDATE
A COUPLE OF SUBTLE SHORTWAVES ARE STILL ON TRACK TO
BRING PRECIPITATION TO THE AREA TODAY. THE FIRST IS OVER
NORTHERN VANCOUVER ISLAND AT THIS HOUR. AS A RESULT, SCATTERED
SHOWERS ARE OBSERVED ACROSS W WA WITH THE BULK OF THE ACTIVITY
OVER THE OLYMPIC PENINSULA AND NORTHERN INTERIOR. THE NEXT
FEATURE WILL TRACK MORE DIRECTLY INTO THE CWA LATER THIS
AFTERNOON-EVENING WITH MORE WIDESPREAD LOWLAND RAINFALL AND
MOUNTAIN SNOW. WINTER WEATHER RELATED HEADLINES WILL REMAIN OVER
THE CASCADES THROUGHOUT THE DAY. THE PREVIOUS DISCUSSION IS
BELOW ALONG WITH AN UPDATED MARINE/AVIATION SECTION:
SYNOPSIS
PERIODS OF LOWLAND RAIN, MOUNTAIN SNOW, AND GUSTY CONDITIONS
WILL CONTINUE THROUGH THE FIRST PART OF THE WEEK AS A SERIES OF
WEATHER SYSTEMS MOVES ACROSS THE REGION. A FEW WEAKER SYSTEMS
LOOK TO MOVE UP INTO THE AREA MID TO LATE WEEK, BUT EXPECT AN
OVERALL TREND TOWARDS COOLER AND DRIER CONDITIONS.
SHORT TERM /TODAY THROUGH TUESDAY/
A BROAD UPPER LEVEL LOW OVER THE GULF OF ALASKA WILL CONTINUE TO
EJECT SHORTWAVES INTO THE REGION THROUGH THE NEAR TERM.
MEANWHILE, AT THE SURFACE, THE NEXT WEAKENING FRONTAL SYSTEM
WILL MOVE ACROSS WESTERN WASHINGTON TODAY, BRINGING THE NEXT
ROUND OF LOWLAND RAIN AND MOUNTAIN SNOW TO THE AREA. SHOWERS
WILL INCREASE IN COVERAGE THROUGH THE MORNING AND AFTERNOON
HOURS AS THE SYSTEM MAKES ITS WAY INTO WESTERN WASHINGTON.
OVERALL RAINFALL AMOUNTS WILL RANGE FROM 0.25-1.00 INCHES ACROSS
THE LOWLANDS, WHILE A FEW SPOTS LIKE PORT TOWNSEND, SEQUIM, AND
WHIDBEY ISLAND WILL LIKELY SEE LOWER AMOUNTS DUE TO RAIN
SHADOWING. ADDITIONAL ROUNDS OF SNOW ARE LIKELY FOR THE
MOUNTAINS, WITH SNOW LEVELS GENERALLY HOVERING BETWEEN 2500-3500
FT THIS MORNING AND FALLING TO 2000-2500 FT BY TONIGHT. HIGHEST
SNOW TOTALS WITH THIS SYSTEM WILL BE ACROSS THE FAR NORTHERN
CASCADES OF WHATCOM AND SKAGIT COUNTIES- WHERE WINTER STORM
WARNINGS ARE IN EFFECT FOR AN ADDITIONAL 1 TO 2 FEET OF SNOW.
SNOW AMOUNTS ACROSS THE CENTRAL CASCADES WILL BE LOWER AND ARE
GENERALLY EXPECTED TO BE BETWEEN 6-12 INCHES, WITH STEVENS AND
SNOQUALMIE PASSES LIKELY ONLY SEEING AROUND 4-6 INCHES, WHILE
WHITE PASS WILL SEE SLIGHTLY HIGHER AMOUNTS BETWEEN 7-9 INCHES.
SOUTHERLY WINDS WILL BECOME BREEZY AGAIN TODAY, PICKING UP
THROUGH THE MORNING HOURS AND GUSTING TO 30-35 MPH. WINDS WILL
REMAIN ELEVATED THROUGH THIS AFTERNOON, BEFORE EASING AGAIN THIS
EVENING.
A MORE ORGANIZED SYSTEM WILL MOVE INTO THE AREA ON MONDAY,
BRINGING STEADIER RAINFALL TO THE LOWLANDS, ADDITIONAL ROUNDS
OF MOUNTAIN SNOW, AND ANOTHER ROUND OF GUSTY WINDS TO WESTERN
WASHINGTON. RAINFALL AMOUNTS WILL GENERALLY BE BETWEEN 0.25-0.50
INCHES ACROSS THE INTERIOR LOWLANDS AND BETWEEN 0.75-1.00 INCHES
ALONG THE COAST. SNOW LEVELS WILL HOVER BETWEEN 2500-3000 FT
FOR ADDITIONAL ROUNDS OF SNOW ACROSS THE OLYMPICS AND CASCADES.
SOUTHERLY WINDS WILL PICK UP AGAIN DURING THE EARLY MORNING
HOURS ON MONDAY. THE STRONGEST WINDS WILL BE ALONG THE COAST AND
FOR AREAS NORTH OF EVERETT, WHERE GUSTS BETWEEN 45-50 MPH WILL
BE POSSIBLE AT TIMES. ELSEWHERE, WIND GUSTS TO 40 MPH WILL BE
POSSIBLE THROUGH THE DAY, BEFORE WINDS GRADUALLY START TO
DECREASE AGAIN ON TUESDAY NIGHT.
LINGERING PRECIPITATION WILL THEN TAPER THROUGH THE DAY ON
TUESDAY. AT THIS TIME, TUESDAY LOOKS TO BRING A QUICK LITTLE
BREAK IN BETWEEN SYSTEMS.
LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/
ENSEMBLES REMAIN IN PRETTY GOOD AGREEMENT WITH THE UPPER LEVEL
TROUGH DIGGING ACROSS THE NORTHEASTERN PACIFIC AND SWINGING
ADDITIONAL DISTURBANCES ACROSS WESTERN WASHINGTON THROUGH THE
LONG TERM. WHILE OVERALL CONDITIONS ARE TRENDING DRIER AS A
WHOLE FOR THE SECOND HALF OF THE WEEK, ADDITIONAL ROUNDS OF
LOWLAND RAIN AND MOUNTAIN SNOW WILL BE POSSIBLE AT TIMES THROUGH
THE PERIOD. THE WEATHER PATTERN ALSO CONTINUES TO FAVOR 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. SHOULD PRECIPITATION OVERLAP WITH THE
COOLER TEMPERATURES, COULD EVEN SEE A FEW SPOTS OF RAIN/SNOW
MIX ACROSS THE LOWLANDS, THOUGH CONFIDENCE IN THIS REMAINS LOW
AT THIS TIME.
14
AVIATION
PERSISTENT TROUGHING OVER THE EASTERN PACIFIC WILL
KEEP WEST-SOUTHWESTERLY FLOW ALOFT OVER W WA BEFORE SHIFTING
MORE DEFINITIVELY SOUTHWESTERLY THIS EVENING. SURFACE WINDS WILL
EASE A LITTLE THIS EARLY MORNING DOWN TO 4-8 KTS FOR MANY
TERMINALS BEFORE SEEING SPEEDS RETURN TO GENERALLY 8-12 KTS WITH
MORE WIND PRONE TERMINALS SUCH AS HQM POTENTIALLY SEEING SOME
GUSTS UP TO 25 STARTING THIS AFTERNOON THROUGH THE REMAINDER OF
THE TAF PERIOD. THROUGH THE MORNING, SHOWERS AND MVFR TO LOW-END
VFR CONDITIONS EXPECTED. AS MORE ORGANIZED PRECIP IS EXPECTED
TO MOVE INTO THE AREA LATE THIS AFTERNOON THROUGH THE REST OF
THE TAF PERIOD, THAT IS LIKELY WHEN WIDESPREAD MVFR TO IFR
CONDITIONS WILL RETURN AND LINGER INTO EARLY MONDAY MORNING.
KSEA...VFR CONDITIONS IN PLACE WITH MAJORITY OF SHOWERS MOVING NORTH
OF THE TERMINAL. SEA-TAC DOES SEEM TO BE JUST ON THE SOUTHERN EDGE
OF THINGS, SO THE VCSH IN THE TAF LOOKS SPOT ON. CIGS MIGHT BE A
LITTLE ON THE PESSIMISTIC SIDE AS LATEST DATA SUGGESTS THAT THE
RETURN TO SHOWERS AND MVFR CONDITIONS MAY HOLD OFF UNTIL 00Z OR A
LITTLE LATER. BEYOND THAT, FORECAST IS ON TRACK. WINDS GENERALLY 5-
10 KTS AND SHOULD REMAIN THAT WAY FOR MUCH OF THE GENERALLY DRY
PERIOD MENTIONED ABOVE. AS LOWER CIGS AND PRECIP MOVE IN, SO TOO
WILL THE STRONGER WINDS WITH SPEEDS INCREASING TO GENERALLY 8-12 KTS.
33/18
MARINE
BORDERLINE SCA WINDS IN THE INTERIOR WATERS TODAY
THROUGH THIS EVENING. A STRONGER PACIFIC STORM SYSTEM IS
SLATED FOR MONDAY WHICH MAY BRING GALES TO THE COASTAL WATERS
AND HEIGHTENED WIND SPEEDS FOR INTERIOR WATERS AS WELL.
INHERITED GALE WATCH FOR THE COASTAL WATERS LOOKS
GOOD...ALTHOUGH WILL ADVISE INCOMING SHIFT THAT A LEAD-UP SCA
FOR LATE TONIGHT MAY NOT BE A BAD IDEA. WINDS OVER THE INTERIOR
WATERS SHOWING BORDERLINE SCA CONDITIONS BUT CONFIDENCE IS NOT
QUITE THERE YET...THUS NO HEADLINE WITH THE MORNING FORECAST.
LOW PRESSURE WILL WEAKENS OFFSHORE TUESDAY ALLOWING FOR OFFSHORE
FLOW WEDNESDAY. THIS OFFSHORE FLOW WILL STRENGTHEN ON THURSDAY
DUE TO HIGH PRESSURE OVER INTERIOR B.C. AND LOW PRESSURE OFF
OR/CA COAST. 33/18
HYDROLOGY
ALTHOUGH SHOWERS ARE EXPECTED OVER W WA TODAY AND
MONDAY, PRECIP AMOUNTS SHOULD NOT INTERFERE WITH THE OVERALL
DOWNWARD TREND BEING SEEN ON MOST AREA RIVERS. RIVERS WITH DAM
REGULATED FLOWS EXPECTED TO REMAIN BELOW FLOOD LEVELS AT THIS TIME,
HOWEVER THE DECISIONS BEHIND RELEASES AND MANAGING RIVER LEVELS IS A
DAY BY DAY THING. AS SUCH, THOSE LIVING NEAR THESE RIVERS SHOULD
REMAIN MINDFUL OF LATEST RIVER FORECASTS AS FLOWS MAY INCREASE FROM
TIME TO TIME 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.
* THE SKOKOMISH RIVER AT POTLATCH 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.
THE MORE SHOWERY NATURE OF PRECIPITATION OVER THE PAST COUPLE OF
DAYS HAS LIMITED THE LANDSLIDE THREAT, HOWEVER THE INCOMING SYSTEM
FOR MONDAY APPEARS TO BE MORE ORGANIZED. THIS MAY BRING A RETURN TO
A HEIGHTENED THREAT FOR LANDSLIDES.
SEW WATCHES/WARNINGS/ADVISORIES
WA...COASTAL FLOOD ADVISORY UNTIL 11 AM PST THIS MORNING FOR SAN
JUAN COUNTY.
WINTER STORM WARNING UNTIL 4 AM PST MONDAY FOR CASCADES OF
WHATCOM AND SKAGIT COUNTIES.
WINTER WEATHER ADVISORY UNTIL 4 AM PST MONDAY FOR CASCADES OF
PIERCE AND LEWIS COUNTIES-CASCADES OF SNOHOMISH AND
NORTHERN KING COUNTIES-CASCADES OF SOUTHERN KING COUNTY.
PZ...SMALL CRAFT ADVISORY UNTIL 10 PM PST THIS EVENING FOR
ADMIRALTY INLET-EAST ENTRANCE U.S. WATERS STRAIT OF JUAN
DE FUCA-NORTHERN INLAND WATERS INCLUDING THE SAN JUAN
ISLANDS-PUGET SOUND AND HOOD CANAL.
GALE WATCH FROM MONDAY MORNING THROUGH MONDAY EVENING 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.
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