643
FXUS66 KSEW 130257
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
755 PM PDT SUN APR 12 2026
SYNOPSIS
WEAK UPPER LEVEL TROUGH MOVING THROUGH LATE TONIGHT INTO MONDAY
MORNING WITH A PUGET SOUND CONVERGENCE ZONE ALSO PRESENT,
DISSIPATING AS THE TROUGH EXITS BY MONDAY AFTERNOON. STRONG FRONT
APPROACHING THE AREA TUESDAY BRINGING THE POSSIBILITY OF HEAVY SNOW
IN THE CASCADES TUESDAY NIGHT. COOL UPPER LEVEL LOW BEHIND THE FRONT
WEDNESDAY AND WEDNESDAY NIGHT BEFORE DRYING NORTHERLY FLOW ALOFT FOR
THE END OF THE WEEK. SPLITTING SYSTEM ARRIVING LATE IN THE WEEKEND.
SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/
W WA SOCKED IN WITH CLOUDS AS PER LATEST SATELLITE IMAGERY THIS
EVENING. LOOKING AT RADAR, A PUGET SOUND CONVERGENCE ZONE HAS
DEVELOPED OVER MUCH OF KING COUNTY AND SOUTHERN PORTIONS OF
SNOHOMISH. WHILE NOT QUITE SHOWING UP ON RADAR JUST YET...STARTING
TO SEE SOME WEAK DEVELOPMENT IN A LINE EXTENDING FROM VANCOUVER
ISLAND TO THE SKAGIT/SNOHOMISH COUNTY LINE. ANY PRECIP FROM THIS
ACTIVITY SHOULD REMAIN LIGHT.
INHERITED FORECAST GENERALLY ON TRACK WITH NO NEED FOR AN EVENING
UPDATE. FOR FORECAST DETAILS, PLEASE REFER TO THE PREVIOUS
DISCUSSION SECTION BELOW. 18
FROM PREVIOUS DISCUSSION...SATELLITE IMAGERY SHOWS MOSTLY CLOUDY
SKIES OVER WESTERN WASHINGTON. DOPPLER RADAR HAS A FEW SHOWERS IN
THE SOUTH CASCADES. TEMPERATURES AT 3 PM/22Z IN THE LOWER TO MID 50S.
CLOUDS STARTING TO BUBBLE UP LATE THIS AFTERNOON BUT WITH
PLENTY OF CLOUD COVER WILL BE HARD TO GENERATE ENOUGH SURFACE
HEATING TO CREATE MUCH IN THE WAY OF SHOWER ACTIVITY THIS
EVENING. SURFACE GRADIENTS TURNED ONSHORE THIS AFTERNOON WITH
ONSHORE FLOW INCREASING TONIGHT. A PUGET SOUND CONVERGENCE ZONE
WILL DEVELOP MOSTLY LIKELY OVER KING COUNTY TONIGHT WITH THE
CONVERGENCE ZONE DRIFTING NORTH EARLY MONDAY MORNING. WEAK UPPER
LEVEL TROUGH ALSO ARRIVING OVERNIGHT INCREASING THE SHOWER
CHANCES OUTSIDE OF THE CONVERGENCE ZONE. LOWS IN THE 40S.
WEAK UPPER LEVEL TROUGH MOVING THROUGH MONDAY MORNING.
CONVERGENCE ZONE OVER SNOHOMISH COUNTY WEAKENING AND MOVING INTO
THE FOOTHILLS. LOW LEVEL ONSHORE KEEPING SKIES AT LEAST MOSTLY
CLOUDY. HIGHS IN THE LOWER TO MID 50S.
UPPER LEVEL LOW AND FRONTAL SYSTEM MOVING OUT OF THE GULF OF
ALASKA MONDAY NIGHT INTO TUESDAY MORNING. WARM FRONT BRUSHING
THE NORTH COAST LATE MONDAY NIGHT. CLOUD COVER WILL KEEP LOWS IN
THE LOWER TO MID 40S.
STRONG COLD FRONT APPROACHING TUESDAY WITH THE FRONT STILL
OFFSHORE LATE TUESDAY AFTERNOON. RAIN STARTING ON THE COAST IN
THE MORNING SPREADING INLAND IN THE AFTERNOON. WINDS PICKING UP
ALONG THE COAST IN THE AFTERNOON. COOL WITH HIGHS NEAR 50.
HAVE ISSUED A WINTER STORM WATCH BEGINNING LATE TUESDAY
AFTERNOON FOR THE CASCADES. SNOW LEVEL NEAR 3000 FEET WITH HEAVY
SNOW POSSIBLE TUESDAY NIGHT AHEAD AND WITH THE FRONT.
BREEZY/WINDY CONDITIONS DEVELOPING WITH THE FRONT FOR THE
LOWLANDS. STRONGEST WINDS ALONG THE COAST AND OVER THE
NORTHWEST INTERIOR. FELTON
LONG TERM /WEDNESDAY THROUGH SUNDAY/
COOL UPPER LEVEL LOW
BEHIND THE FRONT OVER WESTERN WASHINGTON WEDNESDAY MOVING EAST
WEDNESDAY NIGHT. SNOW LEVELS COULD GET AS LOW AS 1500 FEET.
WINTER STORM WATCH CONTINUING FOR THE CASCADES INTO WEDNESDAY
NIGHT FOR ADDITIONAL SIGNIFICANT SNOW ACCUMULATIONS.
DRYING NORTHWESTERLY FLOW ALOFT BEHIND THE UPPER LEVEL LOW
THURSDAY AND FRIDAY. VERY COOL MORNINGS BOTH THURSDAY AND
FRIDAY WITH THE COLDER LOCATIONS GETTING BELOW FREEZING. FROST
ADVISORIES WILL LIKELY BE NEEDED ESPECIALLY THURSDAY MORNING.
WEAK UPPER LEVEL RIDGE MOVING THROUGH SATURDAY AHEAD OF A
SPLITTING FRONT SUNDAY.
AVIATION
WEAK FLOW ALOFT THIS EVENING AND TONIGHT AS AN UPPER LEVEL TROUGH
MOVES THROUGH W WA, BEFORE TURNING MORE NORTH TO NORTHWESTERLY
MONDAY MORNING. SURFACE WINDS AT TERMINALS LARGELY SOUTHWESTERLY,
HOWEVER WESTERLY TO NORTHWESTERLY WINDS FLOWING DOWN THE STRAIT HAS
GIVEN RISE TO SOME PSCZ ACTION OVER KING COUNTY EARLIER THIS EVENING
AND LATEST RADAR TRENDS SUGGEST THAT ANOTHER ROUND OF ACTIVITY MAY
BE SETTING UP OVER PORTIONS OF SKAGIT AND SNOHOMISH COUNTIES.
GENERALLY MVFR CIGS IN PLACE FOR MUCH OF W WA, ALTHOUGH VFR
CONDITIONS STILL IN PLACE OVER NORTHERN PORTIONS OF THE SAN JUANS
AND WHATCOM AND NORTHERN SKAGIT COUNTIES. SHOULD SEE CIGS DIMINISH
OVER THESE AREAS AS WELL OVERNIGHT, HOWEVER THERE IS SOME QUESTION
AS TO WHETHER OR NOT THEY WILL JOIN THE REMAINDER OF THE AREA IN
MVFR CIGS. LATEST MODEL DATA SUGGESTS THAT CIGS SHOULD BECOME
UNIFORMLY MVFR BY MONDAY MORNING AND AS SUCH, FORECAST FOR BLI MAY
NEED TO HAVE CIGS LOWERED FOR THE 06Z ISSUANCE. AS TROUGHINESS A LOW
LEVEL MOISTURE LINGER OVER THE AREA THROUGHOUT MONDAY, SOME
TERMINALS MAY SEE CIGS LIFT SOMEWHAT, BUT PROBABLY NOT ENOUGH TO
LIFT THEM OUT OF MVFR, BEFORE FALLING AGAIN MONDAY EVENING.
KSEA...MVFR CONDITIONS IN PLACE WITH SHOWERS AS THE TERMINAL BEGINS
TO FIND ITSELF ON THE BACKSIDE OF AN EVENING PSCZ. THERE MAY BE A
BIT OF A BREAK FOR THE REMAINDER OF THE EVENING AND INTO EARLY
TONIGHT, HOWEVER WITH ACTIVITY POSSIBLY DEVELOPING TO THE NORTH,
WILL NEED TO KEEP AN EYE ON HOW WELL IT HOLDS TOGETHER IF AND WHEN
IT SHOULD MOVE SOUTHWARD. WINDS SW THIS 4 TO 8 KNOTS THIS EVENING
INTO TONIGHT BEFORE INCREASING TO 8-12 KT WITH GUSTS UP TO 20 KT BY
MONDAY MORNING. MVFR/IFR CIGS ARE TO REMAIN INTO MONDAY AS WELL.
18/MCMILLIAN
MARINE
SURFACE LOW PRESSURE JUST OFF THE N CA COAST AS A HIGH PRESSURE
SYSTEM DEVELOPS OFFSHORE IN THE NORTHEASTERN PACIFIC. ONSHORE FLOW
IS INCREASING AS A SMALL CRAFT ADVISORY REMAINS IN EFFECT FOR
WESTERLIES DOWN THE STRAIT OF JUAN DE FUCA THIS EVENING AND LIKELY
WELL INTO MONDAY. A STRONGER FRONTAL SYSTEM ARRIVING LATE TUESDAY
INTO WEDNESDAY WILL LIKELY YIELD MORE WIDESPREAD HEADLINES AS WE
WILL SEE INCREASED WINDS AND SEAS AND POSSIBLE GALES THROUGH THE
STRAIT. SURFACE HIGH PRESSURE LOOKS TO REBUILD ACROSS THE REGION
TOWARDS THE SECOND HALF OF THE WEEK.
COASTAL SEAS 4 TO 6 FEET THROUGHOUT THE WEEKEND. SEAS WILL THEN
START TO BUILD UPWARDS TO 8 TO 10 FEET BY TUESDAY EVENING AND
REMAINING ELEVATED THROUGH THURSDAY.
MCMILLIAN
HYDROLOGY
NO RIVER FLOODING THE NEXT 7 DAYS.
SEW WATCHES/WARNINGS/ADVISORIES
WA...WINTER STORM WATCH FROM TUESDAY AFTERNOON THROUGH LATE
WEDNESDAY NIGHT 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.
PZ...SMALL CRAFT ADVISORY UNTIL 6 PM PDT MONDAY FOR CENTRAL U.S.
WATERS STRAIT OF JUAN DE FUCA-EAST ENTRANCE U.S. WATERS
STRAIT OF JUAN DE FUCA.
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