954
FXUS66 KSEW 171635
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
935 AM PDT THU SEP 17 2026
SYNOPSIS
HIGH PRESSURE ALOFT AND A THERMAL TROUGH PUSHING INLAND WILL
BRING WARM AND DRY CONDITIONS TO THE INTERIOR OF WESTERN
WASHINGTON TODAY. ONSHORE FLOW WILL RESUME ON FRIDAY, BRINGING
MORE SEASONABLE TEMPERATURES AND MORNING CLOUDS TO THE AREA
THROUGH THE WEEKEND. LIGHT SHOWERS WILL BE POSSIBLE FOR PORTIONS
OF THE AREA EARLY NEXT WEEK AS A WEAK SYSTEM MOVES INTO THE
REGION.
SHORT TERM /TODAY THROUGH SATURDAY/
THE LATEST FORECAST REMAINS ON TRACK THIS MORNING WITH NO
UPDATES. UPPER LEVEL RIDGING WILL CONTINUE TO NUDGE INTO THE
AREA TODAY AS AN UPPER LOW OVER NORTHERN CA/OR STARTS TO LIFT
NORTHEASTWARD TO EXIT THE REGION. A THERMAL TROUGH SITUATED
ALONG THE COAST WILL PUSH INLAND TODAY, ALLOWING FOR OFFSHORE
FLOW TO TRANSITION BACK TO ONSHORE THIS AFTERNOON. A FEW AREAS
OF PATCHY, SHALLOW FOG REMAIN POSSIBLE ACROSS THE AREA EARLY
THIS MORNING WITH GENERALLY LIGHT WINDS ACROSS THE AREA AND SOME
RESIDUAL MOISTURE FROM RECENT RAINS. EXPECT THE EXTENT OF FOG
TO BE LESS THAN THAT OF YESTERDAY, HOWEVER, AS OFFSHORE FLOW
CONTINUES TO PROMOTE DRYING IN THE LOW LEVELS. ANY SHALLOW FOG
THAT DOES DEVELOP WILL DISSIPATE RATHER QUICKLY THIS MORNING.
THE THERMAL TROUGH PUSHING INLAND WILL CONTINUE TO PROMOTE
WARMING ACROSS THE INTERIOR, WITH HIGHS EXPECTED TO BE IN THE
MID TO UPPER 70S FOR MOST SPOTS. A FEW SPOTS, MAINLY ALONG THE
CASCADE VALLEYS AND ACROSS THE SOUTHERN INTERIOR, COULD EVEN
MAKE IT INTO THE LOW 80S THIS AFTERNOON.
ONSHORE FLOW WILL RESUME BY THIS AFTERNOON AND PERSIST INTO THE
WEEKEND, BRINGING SLIGHTLY COOLER, MORE SEASONABLE TEMPERATURES
TO THE AREA ON FRIDAY AND SATURDAY. THE RETURN OF ONSHORE FLOW
WILL ALSO BRING THE RETURN OF MORNING STRATUS TO THE INTERIOR
BOTH DAYS. STRATUS WILL SCATTER AND RETREAT BACK TO THE COAST BY
THE AFTERNOON ON FRIDAY AND LOOKS TO LINGER A BIT LONGER ON
SATURDAY BEFORE GIVING WAY TO SOME AFTERNOON SUN. AFTERNOON
HIGHS WILL BE IN THE LOW TO MID 70S ACROSS THE INTERIOR AND MID
60S ALONG THE COAST BOTH DAYS.
LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/
SEASONABLE TEMPERATURES AND DRY CONDITIONS WILL CONTINUE THROUGH
SUNDAY, WITH ONSHORE FLOW CONTINUING TO PROMOTE MORNING STRATUS
ACROSS THE INTERIOR AND MOSTLY SUNNY AFTERNOONS. ENSEMBLES THEN
HINT AT THE PATTERN CHANGING EARLY NEXT WEEK AS UPPER LEVEL
TROUGHING STARTS TO DEVELOP OVER THE NORTHEASTERN PACIFIC. THIS
SOUTHWEST FLOW ALOFT WILL OPEN THE DOOR FOR SYSTEMS TO MOVE INTO
WESTERN WASHINGTON. AT THIS TIME, THE NEXT WEAK SYSTEM LOOKS TO
APPROACH THE AREA LATER MONDAY INTO TUESDAY AND WILL BRING THE
NEXT CHANCE OF LIGHT RAIN TO THE AREA. SHOWER CHANCES AND SLIGHTLY
COOLER TEMPERATURES, WITH HIGHS IN THE MID 60S TO LOW 70S, THEN
LOOK TO PERSIST INTO MIDWEEK.
14
AVIATION
LIGHT FLOW ALOFT WILL TURN NORTHERLY LATER TODAY AS HIGH PRESSURE
REMAINS CENTERED OFFSHORE WITH AN UPPER LOW WELL SOUTH OF THE
REGION. LIGHT OFFSHORE SURFACE FLOW WILL TURN ONSHORE TONIGHT AS
THERMALLY INDUCED LOW PRESSURE SHIFTS INLAND FROM THE COAST. PATCHY
VALLEY FOG IN OUTLYING AREAS THIS MORNING WILL BURN OFF WITHIN THE
NEXT COUPLE OF HOURS, VFR CONDITIONS WILL PREVAIL TODAY. IFR/LIFR
STRATUS WILL RETURN TO THE IMMEDIATE COAST TONIGHT.
KSEA...VFR. SURFACE WINDS N/NW 8 TO 12 KNOTS TODAY. WINDS WILL BACK
TO LIGHT SOUTHERLY AFTER 06Z TONIGHT.
27/41
MARINE
THERMALLY INDUCED LOW PRESSURE ALONG THE COAST WILL SHIFT INLAND
LATER TODAY. 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.
27
FIRE WEATHER
A THERMAL TROUGH PUSHING INLAND TODAY WILL BRING ONE LAST DAY OF
WARMER AND DRIER CONDITIONS TO 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. THE LOWEST HUMIDITIES WILL BE
CONCENTRATED OVER THE NORTH CASCADES THIS AFTERNOON.
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
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...NONE.
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