381
FXUS66 KSEW 212301
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
301 PM PST SUN DEC 21 2025
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 /TONIGHT THROUGH TUESDAY NIGHT/
ACTIVE CONDITIONS ARE FORECAST THROUGHOUT THE SHORT-TERM
FORECAST AND BEYOND. A BROAD UPPER-LOW REMAINS OVER THE GULF OF
ALASKA AND WILL CONTINUE TO EJECT SHORTWAVES INTO THE REGION
ALLOWING LOWLAND RAIN SHOWERS, MOUNTAIN SNOW, AND BREEZY WINDS
AT TIMES. HREF GUIDANCE HAS A MEAGER AMOUNT OF CAPE PRESENT
ALONG THE COAST, OLYMPICS, AND PART OF THE INTERIOR SO A SLIGHT
CHANCE OF THUNDERSTORMS MUST BE EXPRESSED AS WELL THROUGH
TONIGHT AND MONDAY. SPC HAS AN OUTLINED A GENERAL RISK OF
THUNDER DURING THIS TIME.
OVERALL RAINFALL AMOUNTS FOR THE LOWLANDS THROUGH MONDAY NIGHT
ARE EXPECTED TO BE WITHIN 0.50-1.00 INCH AS A WHOLE, THOUGH
LOCATIONS AROUND AND ADJACENT TO ADMIRALTY INLET WILL LIKELY SEE
LOWER AMOUNTS DUE TO RAIN SHADOWING. SOUTHERLY WINDS WILL
INCREASE ON MONDAY AS A MORE ORGANIZED SYSTEM ARRIVE. WIND GUSTS
UP TO 30-35 MPH WILL BE COMMON ACROSS W WA. WESTERN WHATCOM,
SAN JUANS AND WHIDBEY ISLAND WILL SEE STRONGER GUSTS UP TO 45
MPH.
MCMILLIAN
LONG TERM /WEDNESDAY THROUGH SUNDAY/
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. HOWEVER, DRY BREAKS ARE POSSIBLE WITH TRANSIENT
RIDGING. TOWARDS THE WEEKEND, GUIDANCE IS SIGNALING AN
ATMOSPHERIC RIVER REACHING BC. SO FAR, MOST OF THE MOISTURE
APPEARS TO REMAIN NORTH OF THE CWA BUT UNCERTAINTY REMAINS IN
EXACT DETAILS INCLUDING MOUNTAIN SNOW, RIVER FLOODING, QPF,
ETC.
MCMILLIAN
AVIATION
EASTERN PACIFIC TROUGHING PERSISTS TODAY AND THROUGH THE
START OF THIS WEEK. THIS KEEPS A PERIOD OF OFF-AND-ON LOWLAND RAIN
SHOWERS AND HIGHER ELEVATION SNOWFALL IN THE FORECAST ACROSS WESTERN
WASHINGTON. THE ONGOING BAND OF LIGHT RAINFALL LASTS THROUGH 06Z
THIS EVENING AND BECOMES MUCH MORE LOCALIZED OVERNIGHT MAINLY OVER
THE HIGH TERRAIN AND COASTLINES; TERMINALS ALONG THE SOUND
SHORELINES ARE LIKELY TO REMAIN MAINLY DRY INTO MONDAY MORNING.
EXPECT MVFR CONDITIONS WITH THE RAIN BAND, BOTH VIS AND CIGS, WITH
CIGS IMPROVING TO LOW-END VFR FOR MOST LOWLAND TERMINALS LATE
TONIGHT AND LASTING INTO EARLY MONDAY. SOUTHERLY WINDS REMAIN
ELEVATED TONIGHT BEFORE BECOMING BREEZY MONDAY WITH GUSTS FROM 20-30
KNOTS AFTER 18Z AND LASTING BEYOND THIS TAF PERIOD. THE NEXT ROUND
OF MORE WIDESPREAD RAINFALL IS FORECAST AFTER 21Z MON AND PERSISTING
INTO MONDAY EVENING.
KSEA...ONGOING LIGHT SOUTHWESTERLY WINDS SHIFT BACK TO A SOUTH-
SOUTHEASTERLY FLOW AT THE SURFACE LATER THIS EVENING AS SHOWERS
CLEAR OUT 02-04Z. OVERNIGHT MVFR SKIES REMAIN EXPECTED INTO THE LATE
OVERNIGHT HOURS AHEAD OF CEILINGS LIFTING TO LOW-END VFR OVERNIGHT
THAT LAST INTO MONDAY MORNING. AFTER A MAINLY DRY NIGHT REMAINS
EXPECTED AND LASTS INTO INTO MONDAY MORNING, A FEW RAIN SHOWERS ARE
FORECAST TO BUILD OVER THE AREA TOWARDS 15-18Z. SOUTHERLY WINDS ARE
EXPECTED TO MIX OUT FROM 18-19Z MONDAY AND PRODUCE SOUTHERLY GUSTS
TO 20 KNOTS. THE NEXT ROUND OF HIGHER RAIN SHOWER CHANCES BUILD
AGAIN 22Z MON - 00Z TUES AND LAST INTO THE END OF THE TAF PERIOD.
33/18
MARINE
BREEZY WINDS WILL BE PRESENT ACROSS MOST WATERS THIS
EVENING. A STRONGER SYSTEM WILL BRING ELEVATED WINDS AND SEAS ON
MONDAY - GALE WARNINGS AND SMALL CRAFT ADVISORIES ARE IN
EFFECT. THE FLOW WILL TURN NORTHERLY ON TUESDAY OR TUESDAY NIGHT
IN RESPONSE TO LOW PRESSURE OFF CALIFORNIA. LOW PRESSURE MAY
PASS THROUGH WESTERN WASHINGTON ON WEDNESDAY. NORTH WINDS RETURN
ON THURSDAY AS ANOTHER LOW FORMS TO OUR SOUTH. 33
HYDROLOGY
RIVERS CONTINUE TO SLOWLY RECEDE TODAY. A FEW
RIVERS MAY SEE A SLIGHT RISES DUE TO MONDAY'S RAIN, BUT THE
RIVERS WILL THEN FALL AGAIN THEREAFTER. THE ONLY RIVER THAT
WILL SEE FLOODING BEYOND MONDAY WILL BE THE SKOKOMISH RIVER IN
MASON COUNTY.
SEW WATCHES/WARNINGS/ADVISORIES
WA...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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