681
FXUS66 KSEW 161549
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
849 AM PDT WED SEP 16 2026
SYNOPSIS
HIGH PRESSURE BUILDING INTO THE REGION WITH A THERMAL TROUGH AT
THE SURFACE WILL PROMOTE A WARMING AND DRYING TREND ACROSS WESTERN
WASHINGTON TODAY. THURSDAY WILL BE THE WARMEST DAY OF THE WEEK
ACROSS THE INTERIOR LOWLANDS AS THE THERMAL TROUGH PUSHES INLAND.
THE RETURN OF ONSHORE FLOW WILL BRING NEAR-NORMAL TEMPERATURES
AND MORNING CLOUDS TO THE AREA FRIDAY THROUGH THE WEEKEND. A
WEAK SYSTEM MAY APPROACH THE AREA ON MONDAY.
SHORT TERM /TODAY THROUGH FRIDAY/
THE LATEST FORECAST REMAINS ON TRACK THIS MORNING WITH NO
UPDATES. WARMER AND DRIER CONDITIONS ARE EXPECTED ACROSS
WESTERN WASHINGTON TODAY AS UPPER LEVEL RIDGING NUDGES INTO THE
REGION AND A THERMAL TROUGH AT THE SURFACE REMAINS SITUATED
ALONG THE COAST. LIGHT WINDS AND RESIDUAL MOISTURE IN THE LOW
LEVELS HAVE ALLOWED FOR SOME SPOTS OF PATCHY FOG TO DEVELOP
ACROSS PORTIONS OF THE SOUTHERN INTERIOR AND ALONG THE CASCADE
VALLEYS AND FOOTHILLS EARLY THIS MORNING. EXPECT FOG TO REMAIN
RATHER SHORT- LIVED TODAY AND FOR IT TO SCATTER OUT BY MID
MORNING AS THE LOW LEVELS DRY UNDER OFFSHORE FLOW. SUNNY SKIES
ARE EXPECTED BY MID TO LATE MORNING, WITH AFTERNOON HIGH
TEMPERATURES EXPECTED TO CLIMB INTO THE LOW TO MID 70S FOR THE
MAJORITY OF THE AREA.
THURSDAY WILL BE THE WARMEST DAY OF THE WEEK ACROSS THE INTERIOR
AS THE THERMAL TROUGH ALONG THE COAST PUSHES INLAND. OFFSHORE
FLOW IN THE LOW LEVELS WILL HELP DRY OUT CONDITIONS, SO DO NOT
EXPECT AS MUCH MORNING FOG ACROSS THE AREA. AFTERNOON TEMPERATURES
WILL CLIMB INTO THE MID TO UPPER 70S UNDER SUNNY SKIES AND COULD
APPROACH 80 ACROSS THE CHEHALIS RIVER VALLEY AND ALONG THE CASCADE
VALLEYS. TEMPERATURES WILL COOL A COUPLE DEGREES ALONG THE COAST AS
THE TROUGH PUSHES INLAND AND REINTRODUCES ONSHORE FLOW TO THE AREA,
WITH TEMPERATURES LARGELY EXPECTED TO TOP OUT IN THE LOW 70S.
OVERALL TEMPERATURES WILL COOL AND TREND CLOSER TO NORMAL AGAIN
BY FRIDAY. UPPER LEVEL RIDGING WILL CONTINUE TO NUDGE ITS WAY
INTO THE REGION FROM THE NORTHEASTERN PACIFIC WHILE AN UPPER LOW
OVER NORTHERN CA/EASTERN OR PUSHES OFF TO THE EAST. THE
REINTRODUCTION OF ONSHORE FLOW WILL HELP PUSH MARINE STRATUS
INTO THE INTERIOR FOR A FEW HOURS ON FRIDAY MORNING, BEFORE THE
CLOUDS RETREAT BACK TO THE COAST BY THE AFTERNOON. TEMPERATURES
WILL LARGELY BE IN THE LOW TO MID 70S ACROSS THE INTERIOR AND IN
THE MID 60S ALONG THE COAST.
LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/
NEAR-NORMAL TEMPERATURES AND DRY CONDITIONS WILL CONTINUE OVER
THE WEEKEND AS HIGH PRESSURE OFFSHORE CONTINUES TO INFLUENCE
THE REGION. ONSHORE FLOW IN THE LOW LEVELS WILL PROMOTE MORNING
CLOUD COVER THAT SCATTERS FOR AFTERNOON SUN. A WEAK SYSTEM MAY
APPROACH THE AREA BY MONDAY, THOUGH THERE IS STILL SOME UNCERTAINTY
AMONGST THE ENSEMBLES IN REGARDS TO WHEN EXACTLY THE RIDGE WILL
BREAK DOWN EARLY NEXT WEEK.
14
AVIATION
NORTHEAST FLOW ALOFT CONTINUES TODAY BEFORE BECOMING A BIT VARIABLE
LATE OVERNIGHT AS A CLOSED UPPER LOW DRIFTS SOUTH OF THE REGION AND
UPPER RIDGING CENTERED OFFSHORE BUILDS INTO THE AREA. THE LOW LEVEL
FLOW IS LIGHT NORTHERLY OR WEAKLY OFFSHORE. APART FROM PATCHY
LIFR/IFR STRATUS IN OUTLYING AREAS AND RIVER VALLEYS THAT IS
ACTIVELY DECREASING IN COVERAGE SO FAR THIS MORNING, VFR CONDITIONS
WILL PREVAIL TODAY.
KSEA...VFR TODAY. SURFACE WINDS N/NE 4 TO 6 KNOTS RISING TO
NORTHERLY 9 TO 13 KNOTS BY LATE THIS AFTERNOON.
27/41
MARINE
THERMALLY INDUCED LOW PRESSURE WILL EXPAND NORTHWARD ALONG THE COAST
TODAY THEN SHIFT INLAND THURSDAY AFTERNOON. NORTHERLY OR WEAK
OFFSHORE FLOW WILL TURN ONSHORE THURSDAY NIGHT. LIGHT ONSHORE FLOW
WILL THEN PERSIST FRIDAY THROUGH THE UPCOMING WEEKEND AS A SERIES OF
SYSTEMS PASS WELL NORTH OF THE WATERS.
27
FIRE WEATHER
WARMER AND DRIER CONDITIONS ARE EXPECTED TODAY WITH HIGH PRESSURE
ALOFT NUDGING INTO THE REGION AND A THERMAL TROUGH BUILDING
NORTHWARD ALONG THE COAST AT THE SURFACE. THE TROUGH WILL PROMOTE
WEAK OFFSHORE FLOW, WHICH WILL HELP DRY OUT THE LOW LEVELS THROUGH
THURSDAY. THURSDAY WILL BE THE WARMEST DAY OF THE WEEK ACROSS
THE INTERIOR AS THE TROUGH GRADUALLY PUSHES INLAND. THIS WILL
COINCIDE WITH MINIMUM RELATIVE HUMIDITY VALUES DIPPING DOWN INTO
THE MID 20S TO LOW 30S ACROSS PORTIONS OF THE CASCADES AND LOWLANDS
SOUTH OF PUGET SOUND. THE RETURN OF ONSHORE FLOW BY FRIDAY WILL
THEN HELP MINIMIZE FIRE WEATHER CONCERNS OVER THE WEEKEND AND
INTO EARLY NEXT WEEK.
14
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...NONE.
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