694
FXUS66 KSEW 131541
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
841 AM PDT SAT SEP 13 2025
UPDATE
STRATUS AND PATCHY FOG REMAINS ENTRENCHED ACROSS PARTS
OF W WA INCLUDING THE CHEHALIS RIVER VALLEY, COASTAL AREAS, SAN
JUAN ISLANDS AND NEIGHBORING LOCATIONS. HOWEVER, CLEARING IS
EVIDENT OVER MOST OF THE CASCADES AND ADJACENT LOWLANDS/FOOTHILLS.
WE'RE STILL ON TRACK TO SEE ADDITIONAL CLEARING THIS AFTERNOON BEFORE
THE NEXT DISTURBANCE ARRIVES LATER TONIGHT ALONG THE COAST. HIGHS
TODAY ARE FAVORED TO TOP OUT IN THE 70S THROUGHOUT THE INTERIOR
BUT IN THE 60S ELSEWHERE. THE PREVIOUS DISCUSSION IS BELOW ALONG
WITH AN UPDATED AVIATION SECTION:
SYNOPSIS
HIGH PRESSURE ALOFT WILL SHIFT EAST OF THE REGION
TODAY AND A WEAK FRONT WILL MOVE INTO THE AREA LATE TONIGHT AND
SUNDAY WITH SHOWERS AND COOLER TEMPERATURES. HIGH PRESSURE WILL
REBUILD ACROSS WESTERN WASHINGTON EARLY IN THE COMING WEEK FOR A
BRIEF RETURN OF WARMER AND DRIER CONDITIONS. THE RIDGE WILL
WEAKEN BY MIDWEEK AS ANOTHER WEATHER SYSTEM BRUSHES THE AREA AND
TEMPERATURES RETURN TO NEAR OR A LITTLE BELOW SEASONAL NORMALS.
SHORT TERM /TODAY THROUGH MONDAY/
AN UPPER LEVEL RIDGE OVER
WESTERN WASHINGTON WILL SHIFT EASTWARD INTO THE NORTHERN ROCKIES
TODAY AND WEAKEN AS A FRONTAL SYSTEM OFFSHORE APPROACHES THE
AREA. MORNING CLOUDS WILL GIVE WAY TO SOME PARTIAL SUNSHINE ACROSS
INTERIOR AREAS TODAY, BUT CLOUDS WILL BE SUMMARILY INCREASING BY
EVENING AS THE SYSTEM APPROACHES. MODEL QPF HAS BACKED OFF QUITE
A BIT IN RECENT RUNS...DUE, IN PART, TO THE FACT THAT THE FRONT
WILL SPLIT AS IT MOVES ASHORE EARLY SUNDAY. THIS LEAVES SOME
QUESTION AS TO HOW MUCH PRECIPITATION WILL ACTUALLY MAKE IT EAST
OF PUGET SOUND. HOWEVER, THERE WILL BE SOME POST-FRONTAL
CONVERGENCE ZONE ACTIVITY BY MIDDAY SUNDAY AND THAT OUGHT TO
GENERATE UPWARDS OF A QUARTER TO LOCALLY A HALF INCH OF PRECIP FOR
PORTIONS OF THE CASCADES IN KING AND SNOHOMISH COUNTIES. AS ONE
MIGHT EXPECT, TEMPERATURES WILL TAKE A TUMBLE ON SUNDAY WITH MOST
LOWLAND LOCATIONS STAYING IN THE 60S. UPPER RIDGING BEGINS TO
REBUILD INTO THE AREA SUNDAY NIGHT INTO MONDAY WHILE THERMALLY
INDUCED LOW PRESSURE AT THE SURFACE EXPANDS NORTHWARD ALONG THE
OREGON COAST. THIS WILL LEAD TO DRIER AND SOMEWHAT WARMER
CONDITIONS ON MONDAY.
LONG TERM /TUESDAY THROUGH FRIDAY/
THE PREVIOUSLY MENTIONED
THERMAL TROUGH REACHES THE WASHINGTON COAST ON TUESDAY TURNING THE
LOW LEVEL FLOW OFFSHORE. THIS WILL RESULT IN A PRETTY SHARP,
ALBEIT BRIEF, WARMUP ACROSS WESTERN WASHINGTON WITH BOTH COASTAL
AREAS AND INTERIOR LOCATIONS WARMING INTO THE 70S TO LOWER 80S.
THE FLOW IS EXPECTED TO QUICKLY TURN ONSHORE TUESDAY NIGHT INTO
WEDNESDAY AS ANOTHER WEATHER SYSTEM APPROACHES THE AREA. AND THIS
IS WHERE THE FORECAST DETAILS TURN A LITTLE MURKY. WHILE THERE'S
FAIRLY GOOD AGREEMENT IN THE MODELS THAT COOLER TEMPERATURES WILL
RETURN, THE ENSEMBLES ARE STILL SPLIT WITH RESPECT TO QPF
POTENTIAL. NONETHELESS, THIS DOES APPEAR TO SIGNAL SOMETHING OF
SEASONAL TURNING POINT WITH A MORE ACTIVE PATTERN TAKING SHAPE
OVER THE NORTHEAST PACIFIC. THE BALANCE COULD SOON BEGIN TO TIP
TOWARD AUTUMN. 27
AVIATION
LIGHT WESTERLY FLOW ALOFT WILL TRANSITION SOUTHERLY LATE
TODAY INTO EARLY SUNDAY AS A FRONTAL SYSTEM APPROACHES WESTERN
WASHINGTON. ONSHORE FLOW CONTINUES AT THE SURFACE. LIFR TO MVFR
STRATUS HAS DEVELOPED ACROSS THE AREA THIS MORNING ALONG WITH
PATCHY FOG. SLOW IMPROVEMENT IN CIGS TO VFR FOR SATURDAY
AFTERNOON FOR INTERIOR LOCATIONS WITH INCREASING MID AND HIGH
CLOUDS LATER TODAY. SHOWERS ARE EXPECTED TO REACH THE COAST LATE
TONIGHT INTO SUNDAY MORNING. LIGHT WINDS THIS MORNING WILL
INCREASE FROM THE S/SW THIS AFTERNOON.
KSEA...VFR CONDITIONS REMAIN THIS MORNING OVER THE AIRFIELD BUT
AN LIFR DECK IS JUST WEST OF THE TERMINAL OVER KITSAP COUNTY.
THERE REMAINS SOME UNCERTAINTY INTO HOW EXTENSIVE LOW STRATUS WILL
EXPAND ACROSS PUGET SOUND THIS MORNING SO A TEMPO GROUP IS
PROVIDED THROUGH 17Z FOR THE POTENTIAL OF STRATUS PUSHING OVER
KSEA. OTHERWISE, CIGS ARE EXPECTED TO LIFT BY SATURDAY AFTERNOON,
WITH VFR MID AND HIGH CLOUDS LATER IN THE DAY. LIGHT WINDS THIS
MORNING WILL BECOME S/SW THIS AFTERNOON. JD/MCMILLIAN
MARINE
A WEATHER SYSTEM WILL APPROACH THE COASTAL WATERS TODAY
AND MOVE INLAND ON SUNDAY, RESULTING IN INCREASING WINDS FOR THE
WATERS. SOUTHERLY WINDS WILL PEAK FOR THE COASTAL WATERS THIS
AFTERNOON THROUGH SATURDAY EVENING BEFORE TRANSITIONING TO MORE
NORTHWESTERLY ON SUNDAY. BRIEF SMALL CRAFT ADVISORY WIND GUSTS,
BETWEEN 20 TO 25 KTS, ARE POSSIBLE FOR THE CENTRAL AND NORTHERN
OUTER COASTAL WATERS DURING THIS PERIOD, AND HAVE ISSUED A SCA FOR
THESE AREAS THIS AFTERNOON.
ONSHORE FLOW WILL INCREASE ON SUNDAY, RESULTING IN A WESTERLY PUSH
THROUGH THE STRAIT OF JUAN DE FUCA, WHERE SCA WINDS WILL BE
POSSIBLE. AFTER THE WEATHER SYSTEM MOVES THROUGH, A BRIEF PERIOD OF
OFFSHORE FLOW IS EXPECTED ON TUESDAY BEFORE ANOTHER POTENTIAL FRONT
MIDWEEK.
A DENSE FOG ADVISORY HAS ALSO BEEN ISSUED THROUGH THIS MORNING FOR
THE INNER COASTAL WATERS AND GRAYS HARBOR BAR WITH VISIBILITIES
LESS THAN 1 NM FOR THESE AREAS.
SEAS WILL REMAIN 6 TO 8 FEET THROUGH THE WEEKEND, WITH A PERIOD
DROPPING TO NEAR 8 SECONDS BRIEFLY TONIGHT. SEAS WILL THEN SUBSIDE
TO 4 TO 6 FEET MONDAY BEFORE BUILDING MIDWEEK. JD
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...DENSE FOG ADVISORY UNTIL 11 AM PDT THIS MORNING FOR COASTAL
WATERS FROM CAPE FLATTERY TO JAMES ISLAND OUT 10 NM-COASTAL
WATERS FROM JAMES ISLAND TO POINT GRENVILLE OUT 10 NM-
COASTAL WATERS FROM POINT GRENVILLE TO CAPE SHOALWATER OUT
10 NM-GRAYS HARBOR BAR.
SMALL CRAFT ADVISORY UNTIL 8 PM PDT THIS EVENING FOR COASTAL
WATERS FROM CAPE FLATTERY TO JAMES ISLAND 10 TO 60 NM-
COASTAL WATERS FROM JAMES ISLAND TO POINT GRENVILLE 10 TO
60 NM.
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