233
FXUS66 KSEW 210312
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
812 PM PDT SUN SEP 20 2026
SYNOPSIS
AN UPPER RIDGE REMAINS IN PLACE ACROSS THE PACIFIC
NORTHWEST THROUGH TONIGHT. THE RIDGE FLATTENS MONDAY INTO
TUESDAY AS A FRONTAL SYSTEM TRACKS INTO BRITISH COLUMBIA.
DEEPER TROUGHING DEVELOPS LATER THURSDAY INTO FRIDAY FOR MORE
WIDESPREAD PRECIPITATION POTENTIAL.
SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/
THE CURRENT
FORECAST REMAINS ON TRACK WITH NO PLANNED UPDATES TONIGHT. 33
PREVIOUS DISCUSSION...MOSTLY SUNNY SKIES THIS AFTERNOON WITH
LINGERING STRATUS CLEARING ACROSS PORTIONS OF SOUTHWEST
WASHINGTON. DRY CONDITIONS THROUGH TONIGHT WITH AN UPPER RIDGE
OVER THE PACIFIC NORTHWEST. TEMPERATURES PEAKING IN THE 60S TO
LOW 70S TODAY.
ANOTHER ROUND OF STRATUS IS EXPECTED MONDAY MORNING ACROSS
WESTERN WASHINGTON, CLEARING FOR SOME AFTERNOON SUNSHINE. THE
UPPER RIDGE ALSO SHIFTS EASTWARDS ON MONDAY AS A FRONTAL SYSTEM
MOVES INTO BRITISH COLUMBIA. THIS WILL RESULT IN INCREASED
ONSHORE FLOW LATE MONDAY INTO TUESDAY FOR ADDITIONAL CLOUDS.
TEMPERATURES MONDAY AND TUESDAY WILL PEAK IN THE 60S TO LOW
70S.
LONG TERM /WEDNESDAY THROUGH SUNDAY/
A WEAKENING FRONTAL
SYSTEM BRUSHES THE AREA LATE TUESDAY NIGHT THROUGH WEDNESDAY,
BRINGING SLIGHT POPS TO NORTHERN PORTIONS OF THE OLYMPIC
PENINSULA AND SKAGIT COUNTY NORTHWARDS. TROUGHING DEEPENS
OFFSHORE THURSDAY AS A MORE ORGANIZED SYSTEM APPROACHES THE
PACIFIC NORTHWEST. ENSEMBLES ARE CONSISTENT IN TROUGHING
OVERHEAD INTO FRIDAY, ALTHOUGH SOME UNCERTAINTY REMAINS INTO THE
DEPTH OF THE TROUGH. EITHER WAY, MORE WIDESPREAD PRECIPITATION
POTENTIAL EXISTS THURSDAY NIGHT INTO FRIDAY ASSOCIATED WITH THE
FRONTAL SYSTEM MOVING ACROSS THE PACIFIC NORTHWEST. SNOW LEVELS
DURING THIS PERIOD RANGE 6500 TO 8000 FEET RESULTING IN HIGH
ELEVATION MOUNTAIN SNOWFALL. ENSEMBLES SUGGEST A WEAK TROUGHING
TO ZONAL FLOW SIGNAL BY NEXT WEEKEND, WITH PREDOMINANTLY DRIER
CONDITIONS AND COOLER TEMPERATURES. JD
AVIATION
WIDESPREAD VFR CONDITIONS THIS EVENING CONTINUING
OVERNIGHT FOR THE INTERIOR TERMINALS. ANOTHER ROUND OF MARINE
STRATUS CLOUDS IS FORECAST TO ARRIVE LATE TONIGHT INTO EARLY MONDAY
MORNING, BUT LOOKS TO PRIMARILY IMPACT COASTAL TERMINALS, GETTING AS
FAR IN AS KPWT AND KOLM BY THE MORNING. PATCHY LOW CIGS/FOG ARE
POSSIBLE FOR THE REST OF THE PUGET SOUND TERMINALS TOMORROW MORNING,
GENERALLY AFTER 12Z, WITH THE PROBABILITIES FOR MVFR CIGS AROUND
20%. PROBABILITIES OF IFR/LIFR CIGS ALONG THE COAST AND WESTERN
PUGET SOUND AREA ARE FAVORED (60% OR MORE). WIDESPREAD VFR EXPECTED
AFTER 17Z-20Z. SURFACE WINDS ARE EXPECTED TO BECOME MORE
SOUTHWESTERLY FOR MUCH OF THE AREA AFTER 12Z TOMORROW MORNING AT 3-6
KTS.
KSEA...VFR CONDITIONS CONTINUE THIS EVENING AND INTO MONDAY. CLEAR
SKIES ARE FORECAST OVERNIGHT. THE MARINE STRATUS ISN'T FAVORED TO
REACH THE TERMINAL TOMORROW MORNING, BUT THE TAF WILL INDICATE SOME
LOWER CLOUDS (NOT A CEILING AT THIS TIME) AFTER 12Z. PATCHY FOG MAY
DEVELOP NEAR OR AT THE TERMINAL MONDAY MORNING. HOWEVER, NOT
EXPECTING VISIBILITY TO REDUCE BELOW 6SM. AREAS WEST AND SOUTH OF
THE TERMINAL WILL HAVE A HIGHER LIKELIHOOD OF SEEING LOWER CIGS AND
REDUCED VISIBILITY. LIGHT NORTHERLY WINDS GENERALLY BELOW 5 KT
TONIGHT. SURFACE WINDS WILL BECOME MORE SOUTH TO SOUTHWESTERLY AFTER
12Z, CONTINUING INTO TOMORROW AFTERNOON AT 4-7 KTS.
21/29
MARINE
HIGH PRESSURE WILL PERSIST OVER THE OFFSHORE WATERS
INTO MONDAY. A WEAK FRONT MOVES INTO BRITISH COLUMBIA LATER
MONDAY INTO TUESDAY, RESULTING IN INCREASED ONSHORE FLOW.
PROBABILITIES FOR SMALL CRAFT ADVISORY WEST WIND GUSTS RANGE
BETWEEN 70 TO 90% MONDAY NIGHT FOR THE CENTRAL AND EASTERN
STRAIT OF JUAN DE FUCA, AND FOR THIS REASON ISSUED A SCA FOR
THESE AREAS. ANOTHER WESTERLY PUSH IS EXPECTED TUESDAY NIGHT,
BUT AT THIS TIME THE STRONGER WINDS ARE CONFINED TO THE CANADIAN
SIDE OF THE STRAIT. A WEAKENING FRONT THEN MOVES ACROSS THE
WATERS ON WEDNESDAY, WITH ANOTHER WEATHER SYSTEM LATE THURSDAY
INTO FRIDAY.
SEAS OF 3 TO 5 FEET THROUGH MONDAY MORNING WILL BUILD TO 7 TO 9
FEET MONDAY NIGHT AS A LONGER PERIOD NORTHWESTERLY SWELL ARRIVES
ACROSS THE COASTAL WATERS. BRIEF 10 FOOT SEAS MAY OCCUR OVER THE
OUTER COASTAL WATERS MONDAY NIGHT. SEAS THEN SUBSIDE TO 6 TO 8
FEET TUESDAY AFTERNOON THROUGH FRIDAY. JD
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...SMALL CRAFT ADVISORY FROM 3 PM MONDAY TO MIDNIGHT PDT MONDAY
NIGHT FOR CENTRAL U.S. WATERS STRAIT OF JUAN DE FUCA-EAST
ENTRANCE U.S. WATERS STRAIT OF JUAN DE FUCA.
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