955
FXUS66 KSEW 180309
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
809 PM PDT THU SEP 17 2026
SYNOPSIS
A THERMAL TROUGH WILL CONTINUE TO MOVE INLAND TODAY, PROMOTING
WARMER TEMPERATURES ACROSS THE INLAND LOWLANDS. ONSHORE FLOW
WILL RETURN ON FRIDAY, BRINGING MORE SEASONABLE AND DRY
CONDITIONS WITH MORNING CLOUDS THROUGH THE WEEKEND AND
POTENTIALLY INTO EARLY NEXT WEEK. LIGHT RAIN IS POSSIBLE ON
MONDAY, WITH A POTENTIAL PATTERN CHANGE ON TAP BY THE END OF
NEXT WEEK.
SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/
AS AN UPPER LEVEL RIDGE CONTINUES TO NUDGE INTO THE PACIFIC
NORTHWEST, A THERMAL TROUGH WILL CONTINUE TO SHIFT INLAND TODAY
BRINGING THE WARMEST TEMPERATURES OF THE WEEK OVER THE INTERIOR.
HIGH TEMPERATURES ARE ON TRACK TO PEAK IN THE MID TO UPPER 70S
TODAY, WITH SOME AREAS IN THE CASCADE VALLEYS AND FOOTHILLS AND
SOUTH OF THE PUGET SOUND REACHING THE LOW 80S. AS THE THERMAL
TROUGH PROGRESSES FURTHER INLAND, ONSHORE FLOW WILL RESUME,
BRINGING A MORE FALL-LIKE WEATHER PATTERN TO THE REGION.
ONSHORE FLOW WILL CONTINUE THROUGH SATURDAY AS A RIDGE OF HIGH
PRESSURE GRADUALLY SHIFTS EASTWARD. THIS WILL BRING A MORE
SEASONABLE PATTERN TO WESTERN WASHINGTON, WITH DAILY LOW STRATUS
EXPANDING INLAND AND ERODING BY THE AFTERNOON AND HIGHS IN THE
LOW TO MID 70S FOR THE LOWLANDS. AREAS ALONG THE COASTLINE MAY
NOT BREAK OUT OF STRATUS DEPENDING ON THE STRENGTH OF THE MARINE
PUSH EACH MORNING, WITH HIGHS IN THE MID TO UPPER 60S EACH DAY.
LONG TERM /SUNDAY THROUGH THURSDAY/
SUNDAY WILL BRING MORE OF THE SAME, AS SOUTHWEST FLOW ALOFT
CONTINUES TO PROMOTE ONSHORE FLOW AT THE SURFACE. MOSTLY DRY
CONDITIONS MAY EVEN CONTINUE INTO THE MIDDLE OF NEXT WEEK, AS A
SERIES OF SYSTEMS MOVE INLAND TO THE NORTH OVER BRITISH
COLUMBIA. ENSEMBLES CONTINUE TO SHOW CHANCES FOR LIGHT
PRECIPITATION IN WESTERN WASHINGTON ON MONDAY, BUT CONFIDENCE IS
LOW. TOWARDS THE END OF THE WEEK, POTENTIAL INCREASES FOR A
PATTERN CHANGE THAT COULD BRING COOLER TEMPERATURES AND
WIDESPREAD CHANCES FOR PRECIPITATION TO THE REGION.
15
AVIATION
LIGHT AND VARIABLE FLOW ALOFT TURNING NORTHERLY LATER THIS EVENING
AS AN UPPER-RIDGE BUILDS INTO THE REGION. VFR AREA WIDE THIS
EVENING. LOW- LEVEL FLOW WILL TURN ONSHORE TONIGHT AS A PUSH OF
MARINE STRATUS AND AREAS OF FOG WILL MOVE IN (LIFR/IFR). THE
ACTIVITY WILL START ALONG THE COAST BY 04-06Z FRIDAY AND SPREAD
TOWARDS THE INLAND TERMINALS BETWEEN 08-14Z. ANY LINGERING
STRATUS SHOULD BURN OFF TO A RETURN OF VFR BY 20-21Z BUT WILL
REMAIN STUBBORN ALONG THE COAST. MORE LOW STRATUS AGAIN LIKELY
EARLY SATURDAY MORNING. WINDS THIS EVENING/TONIGHT WILL BECOME
VARIABLE, BUT TURN TO THE SOUTHWEST 4-8 KT FRIDAY.
KSEA...VFR AT THE TERMINAL THROUGHOUT THE EVENING. SURFACE WINDS
W/NW 5 TO 10 KNOTS TODAY. WINDS WILL BACK TO LIGHT SOUTHERLY AFTER
06Z TONIGHT. LOW STRATUS (30% CHANCE OF IFR CONDITIONS) REMAINS
ON TRACK TO ARRIVE AROUND 12-14Z FRIDAY MORNING BUT SHOULD BURN
OFF BY 19-20Z TO VFR. MORE LOW STRATUS AGAIN A POSSIBILITY
EARLY SATURDAY MORNING.
41/HPR
MARINE
THERMALLY INDUCED LOW PRESSURE ALONG THE COAST IS SHIFTING INLAND
THIS AFTERNOON. AS A RESULT, NORTHERLY OR WEAK OFFSHORE FLOW WILL
TURN ONSHORE TONIGHT. 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.
SEAS GENERALLY 4 TO 6 FT WITH 7 FT WAVES POSSIBLE FOR THE OUTER
WATERS THROUGHOUT THIS TIME.
41
FIRE WEATHER
A THERMAL TROUGH PUSHING INLAND TODAY WILL BRING ONE LAST DAY OF
WARMER AND DRIER CONDITIONS THROUGHOUT THE INTERIOR. OFFSHORE
FLOW WILL GRADUALLY TRANSITION BACK TO ONSHORE THIS AFTERNOON,
THOUGH RELATIVE HUMIDITY VALUES STILL LOOK TO DIP INTO THE 20S
AND 30S ACROSS PORTIONS OF THE CASCADES, WITH THE LOWEST
HUMIDITIES CONCENTRATED OVER THE NORTH CASCADES.
ONSHORE FLOW WILL THEN BRING COOLER TEMPERATURES AND INCREASED
MOISTURE TO THE AREA FRIDAY THROUGH THE WEEKEND, HELPING TO
MINIMIZE FIRE WEATHER CONCERNS INTO EARLY NEXT WEEK.
14/MAZURKIEWICZ
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...NONE.
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