454
FXUS66 KSEW 220355
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
755 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 TONIGHT 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 EXITS THE
AREA IN THE NEXT FEW HOURS AS A COLD FRONT MOVES ONSHORE. AS A
RESULT EXPECT SHOWER ACTIVITY TO BECOME MORE LOCALIZED OVERNIGHT
MAINLY OVER THE HIGH TERRAIN AND COASTLINES; TERMINALS ALONG THE
SOUND SHORELINES ARE FORECAST TO REMAIN MAINLY DRY INTO MONDAY
MORNING. MVFR CONDITIONS ASSOCIATED WITH THESE LAST FEW HOURS OF
WIDESPREAD SHOWERS IMPROVE FROM 06-09Z TONIGHT...LASTING INTO MONDAY
MORNING. SOUTHERLY WINDS AT 5-10 KNOTS TONIGHT INCREASE AND WILL BE
BREEZY MONDAY MID-DAY ONWARD WITH GUSTS FROM 20-30 KNOTS. THE NEXT
ROUND OF MORE WIDESPREAD RAINFALL IS FORECAST AFTER 21Z MON AND
PERSISTS THROUGH TUES 06Z.
KSEA...THE MOST WIDESPREAD SHOWER ACTIVITY TONIGHT HAS ENDED AND
WILL BE WIDELY SCATTERED THROUGH 06/07Z TONIGHT. MVFR SKIES BEGIN TO
LIFT TO LOW-END VFR 06-09Z TONIGHT THAT LAST INTO MONDAY MORNING.
THE LATE NIGHT MAINLY DRY CONDITIONS LAST 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 18-20Z MONDAY AND
PRODUCE SOUTHERLY GUSTS TO 20 KNOTS. THE NEXT ROUND OF MORE
WIDESPREAD RAIN SHOWER CHANCES BUILD AGAIN 22Z MON - 00Z TUES AND
LAST THROUGH 05-07Z. PERIODS OF MVFR VISIBILITY IS LIKELY WITH THESE
LATE MONDAY PM SHOWERS AND VFR CEILINGS DECREASE TO MVFR 00Z - 03Z
TUE AND LAST MONDAY NIGHT.
MARINE
WINDS HAVE MOSTLY EASED ACROSS THE AREA BUT GUSTS UP TO SMALL
CRAFT STRENGTH ARE HOLDING ON THROUGH THE PUGET SOUND TONIGHT.
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. 33/62
HYDROLOGY
RIVERS CONTINUE TO SLOWLY RECEDE TODAY AND ONLY THE SKOKOMISH
REMAINS IN FLOOD STAGE AS OF TONIGHT. 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...COASTAL FLOOD ADVISORY FROM 6 AM TO NOON PST MONDAY FOR SAN
JUAN COUNTY.
WIND ADVISORY FROM 10 AM TO 7 PM PST MONDAY FOR ISLAND COUNTY-
LOWLANDS OF WESTERN SKAGIT AND NORTHWESTERN SNOHOMISH
COUNTIES-LOWLANDS OF WESTERN WHATCOM COUNTY-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.
WIND ADVISORY FROM 10 AM TO 4 PM PST MONDAY FOR NORTHERN
WASHINGTON COAST.
PZ...SMALL CRAFT ADVISORY FROM 1 PM MONDAY TO 10 AM PST TUESDAY FOR
GRAYS HARBOR BAR.
SMALL CRAFT ADVISORY FROM 4 AM MONDAY TO 4 AM PST TUESDAY FOR
ADMIRALTY INLET-NORTHERN INLAND WATERS INCLUDING THE SAN
JUAN ISLANDS-PUGET SOUND AND HOOD CANAL-WEST ENTRANCE
U.S. WATERS STRAIT OF JUAN DE FUCA.
SMALL CRAFT ADVISORY FROM 10 AM MONDAY TO 4 AM PST TUESDAY FOR
CENTRAL U.S. WATERS STRAIT OF JUAN DE FUCA.
GALE WARNING FROM 4 AM TO 10 PM PST MONDAY 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-EAST ENTRANCE U.S.
WATERS STRAIT OF JUAN DE FUCA.
SMALL CRAFT ADVISORY UNTIL 10 PM PST THIS EVENING FOR PUGET
SOUND AND HOOD CANAL.
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