083
FXUS66 KSEW 170255
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
755 PM PDT WED SEP 16 2026
SYNOPSIS
HIGH PRESSURE ALOFT WITH A THERMAL TROUGH BUILDING ALONG THE
COAST WILL PROMOTE A WARMING AND DRYING TREND THROUGH THURSDAY.
ONSHORE FLOW WILL RESUME ON FRIDAY, WITH SEASONABLE
TEMPERATURES AND MORNING CLOUDS THROUGH THE WEEKEND. A WEAK
SYSTEM MAY BRING LIGHT SHOWERS NEAR THE CANADA BORDER MONDAY,
WITH CONTINUED DRY CONDITIONS AND ONSHORE FLOW FAVORED BEYOND.
SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/
AS A LOW PRESSURE SYSTEM CONTINUES TO MOVE SOUTHWARD OVER THE
WESTERN US, AN UPPER LEVEL RIDGE WILL CONTINUE TO BUILD INTO
WESTERN WASHINGTON. TEMPERATURES TODAY WILL PEAK RIGHT AROUND
NORMAL FOR MID SEPTEMBER, WITH HIGHS IN THE MID TO UPPER 70S
ACROSS THE LOWLANDS AND IN THE 60S ALONG THE IMMEDIATE
COASTLINE. CLEAR SKIES WILL CONTINUE THROUGHOUT THE DAY AND INTO
THE OVERNIGHT HOURS, AND COMBINED WITH LIGHT WINDS AND SOME
REMAINING RESIDUAL MOISTURE FROM RECENT RAINS, AREAS OF PATCHY
FOG ARE POSSIBLE ONCE AGAIN EARLY THURSDAY MORNING. HOWEVER, ANY
FOG THAT DEVELOPS WILL BE SHALLOW AND SHORT-LIVED, AS WEAK
OFFSHORE FLOW CONTINUES TO PROMOTE ADDITIONAL DRYING. THURSDAY
WILL BRING SIMILAR CONDITIONS TO TODAY, WITH CLEAR SKIES AND
LIGHT WINDS. A THERMAL TROUGH SHIFTING INLAND THROUGHOUT THE DAY
THURSDAY WILL PROMOTE ADDITIONAL WARMING, WITH HIGHS REACHING
THE MID TO UPPER 70S FOR MOST INLAND AREAS. SOME SPOTS ALONG THE
CASCADE FOOTHILLS AND VALLEYS AND OVER THE SOUTH INTERIOR COULD
REACH THE LOWER 80S.
ONSHORE FLOW WILL RESUME LATE THURSDAY AS THE UPPER LOW OVER THE
SOUTHWESTERN US SHIFTS FURTHER INLAND AND HIGH PRESSURE
CONTINUES TO BUILD OVERHEAD. THIS WILL RESUME MORE SEASONABLE
TEMPERATURES, AND A MARINE PUSH EARLY FRIDAY MORNING THAT WILL
BLANKET AT LEAST SOME OF THE INTERIOR LOWLANDS. CONDITIONS ARE
FAVORED TO IMPROVE BY FRIDAY AFTERNOON, WITH ANOTHER ROUND OF
MOSTLY SUNNY SKIES ACROSS MOST OF THE REGION, THOUGH THE
IMMEDIATE COAST MAY STAY CLOUDY THROUGHOUT THE DAY.
LONG TERM /SATURDAY THROUGH WEDNESDAY/
NORTHWEST FLOW ALOFT WILL CONTINUE OVER THE PACIFIC NORTHWEST
THROUGH THE WEEKEND AS THE UPPER LEVEL RIDGE SHIFTS EASTWARD.
ONSHORE FLOW WILL CONTINUE TO PROMOTE VARYING DEGREES OF MORNING
LOW STRATUS AND MOSTLY SUNNY AFTERNOONS, WITH HIGH TEMPERATURES
IN THE UPPER 60S TO LOWER 70S. ENSEMBLES MAINTAIN A SLIGHT
CHANCE OF LIGHT RAIN ON MONDAY OVER HIGHER TERRAIN NEAR THE
CANADA BORDER, THOUGH UNCERTAINTY STILL REMAINS OVER THE EXTENT
OF RAIN, IF ANY. DRY CONDITIONS ARE FAVORED TO CONTINUE INTO THE
MIDDLE OF NEXT WEEK WITH SLIGHTLY COOLER TEMPERATURES AND SUN
BREAKS IN THE AFTERNOONS.
15
AVIATION
NORTHEAST FLOW ALOFT CONTINUES THIS AFTERNOON BEFORE TURNING
VARIABLE LATE OVERNIGHT. A RETURN TO MORE NORTHERLY FLOW IS EXPECTED
DURING THE DAY ON THURSDAY AS AN UPPER-RIDGE BUILDS IN. VFR THIS
AFTERNOON AND FOR MOST TONIGHT. PATCHY VALLEY FOG LOOKS TO DEVELOP
IN THE EARLY MORNING HOURS ON THURSDAY BUT SHOULD BURN OFF BY 17-
18Z. CAN'T RULE OUT ISOLATED POCKETS OF LIFR/IFR CONDITIONS FOR
TERMINALS ADJACENT/WITHIN VALLEYS (KHQM), AS WELL AS NORTH AND
EAST OF KPAE, AND AROUND KOLM. VFR ALL AREAS AGAIN ON THURSDAY
WITH LIGHT OFFSHORE FLOW.
KSEA...VFR TODAY AND LASTING OVERNIGHT INTO THURSDAY. FOG TO
REMAIN EAST OF THE TERMINAL IN THE MORNING. SURFACE WINDS N/NE
AROUND 8 TO 12 KNOTS THIS AFTERNOON. WINDS DECREASE TO 3 TO 6
KNOTS OVERNIGHT INTO THURSDAY MORNING - RETURNING 4 TO 8 KNOTS.
41/HPR
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. THE TREND WILL LIKELY PERSIST
INTO EARLY NEXT WEEK. GENERALLY BENIGN SEAS ARE EXPECTED.
41
FIRE WEATHER
WARM AND DRY CONDITIONS TODAY WITH HIGH PRESSURE ALOFT NUDGING
INTO THE REGION AND A SURFACE THERMAL TROUGH ALONG THE COAST.
THE THERMAL TROUGH WILL PROMOTE WEAK OFFSHORE FLOW, WHICH WILL
HELP DRY OUT THE LOW LEVELS THROUGH THURSDAY. THE WARMEST DAY IS
ON TRACK TO BE THURSDAY, WHICH WILL COINCIDE WITH MINIMUM
RELATIVE HUMIDITY DECREASING INTO THE LOW 20S TO LOW 30S ACROSS
PORTIONS OF THE CASCADES. THE LOWEST HUMIDITIES WILL BE
CONCENTRATED OVER THE NORTHERN CASCADES. THE RETURN OF ONSHORE
FLOW BY FRIDAY WILL HELP MINIMIZE FIRE WEATHER CONCERNS OVER THE
WEEKEND AND INTO EARLY NEXT WEEK AS COOLER AND MORE MOIST
CONDITIONS RETURN.
29/14
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...NONE.
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