555
FXUS66 KSEW 172152
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
252 PM PDT WED JUN 17 2026
SYNOPSIS
AN UPPER-LEVEL RIDGE CENTERED OFFSHORE WITH NORTHWESTERLY FLOW
ALOFT AND LIGHT LOW LEVEL FLOW WILL ALLOW TEMPERATURES TO TREND
WARMER THROUGH FRIDAY. COOLER TEMPERATURES ARE EXPECTED FOR
SATURDAY AND SUNDAY BEFORE MUCH WARMER TEMPERATURES RETURN FOR
MONDAY AND TUESDAY. ELEVATED FIRE WEATHER CONDITIONS ARE
EXPECTED MONDAY AND TUESDAY.
SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/
AN UPPER-LEVEL RIDGE IS CENTERED OFFSHORE THE PACIFIC NORTHWEST
WITH BROAD TROUGHING OVER CENTRAL CANADA THIS AFTERNOON.
THROUGH THURSDAY, WESTERN WASHINGTON WILL BE UNDER SUBTLE
RIDGING WITH NORTHWEST FLOW ALOFT. ONSHORE FLOW WILL WEAKEN
TONIGHT WITH LESS STRATUS COVERAGE THURSDAY MORNING.
TEMPERATURES TREND WARMER THURSDAY WITH HIGHS IN THE 70S ALONG
THE COAST AND IN THE UPPER 70S AND MID 80S ACROSS THE INTERIOR.
RIDGING AMPLIFIES EASTWARD ON FRIDAY AS A LOW PRESSURE SYSTEM
AND ASSOCIATED COLD FRONT NEARS THE PACIFIC NORTHWEST COAST. A
RETURN OF SLIGHTLY STRONGER ONSHORE FLOW ON FRIDAY WILL RESULT
IN COOLER TEMPERATURES ALONG THE COAST WITH WARMER TEMPERATURES
INLAND. INLAND HIGHS IN THE UPPER 70S TO MID 80S BRINGS
WIDESPREAD MINOR HEATRISK TO THE REGION WITH POCKETS OF MODERATE
HEATRISK IN THE SEATTLE METRO AREA.
VMT
LONG TERM /SATURDAY THROUGH WEDNESDAY/
WESTERN WASHINGTON WILL BE UNDER THE INFLUENCE OF BROAD
TROUGHING ON SATURDAY WITH TEMPERATURES COOLING BY 5-10 DEGREES.
THIS WILL BE SHORT-LIVED AS ENSEMBLES ARE IN GOOD AGREEMENT FOR
AN AMPLIFIED UPPER-LEVEL RIDGE OFFSHORE TO BEGIN SHIFTING
INLAND EARLY NEXT WEEK. 25TH-75TH PERCENTILE MAXIMUM
TEMPERATURE SPREAD IS AROUND 4-5 DEGREES ACROSS THE INLAND
AREAS, LEADING TO HIGH CONFIDENCE FOR HIGH TEMPERATURES IN THE
UPPER 80S TO LOW 90S FOR MONDAY AND TUESDAY. CONFIDENCE IS LOWER
ACROSS THE COAST WHERE 25TH-75TH SPREAD IS BETWEEN 8-11
DEGREES. THIS STEMS FROM UNCERTAINTY IN THE STRENGTH OF THE
THERMALLY INDUCED SURFACE PRESSURE TROUGH AND ITS INFLUENCE ON
THE STRENGTH OF THE OFFSHORE FLOW. THERE IS HIGH CONFIDENCE
(90-100% CHANCE) FOR WIDESPREAD MODERATE HEATRISK FOR THE INLAND
AREAS WITH A LOW CHANCE (20-30%) FOR MAJOR HEATRISK IN THE
SEATTLE METRO AREA.
CONFIDENCE IN THE SYNOPTIC PATTERN DECREASES ON WEDNESDAY WITH
AROUND 40 PERCENT OF ENSEMBLES SUGGESTING A BREAKDOWN OF THE
UPPER-LEVEL RIDGE BRINGING COOLER TEMPERATURES. THE OTHER 60%
HOLDS ONTO SOME DEGREE OF RIDGING WITH WARMER TEMPERATURES
CONTINUING INTO WEDNESDAY AND BEYOND. THIS IS ALSO REFLECTED IN
THE 25TH-75TH PERCENTILE MAX TEMPERATURE SPREAD INCREASING TO
8-11 DEGREES ACROSS MOST OF WESTERN WASHINGTON.
VMT
AVIATION
STRONG NORTHWEST FLOW ALOFT WILL CONTINUE JUST NORTH OF THE
TERMINALS WITH HIGHER SURFACE PRESSURE OFF THE COAST KEEPING THE
PATTERN ONSHORE. CLOUDS WILL CONTINUE TO SCATTER OUT THIS AFTERNOON
WITH CONDITIONS BECOMING VFR (FEW LINGERING AREAS OF MVFR REMAIN
THIS AFTERNOON WEST OF PUGET SOUND BUT WERE SCATTERING OUT). WINDS
WILL CONTINUE TO SHIFT THIS AFTERNOON TO THE WEST AND NORTHWEST AS
STRONGER WINDS ALOFT MIX DOWN. AT THE SURFACE, 5-10 KT WITH AN
ISOLATED GUST TO 20 KT BEING POSSIBLE THROUGH THE EVENING. FOR
THURSDAY MORNING, THE INTERIOR HAS A 10-20% CHANCE OF MVFR CIGS IN
THE MORNING, WHILE THE COAST HAS A 30-40% CHANCE OF IFR CEILINGS
OVERNIGHT. CLEARING TIME FOR ANY LOW CIGS IS BY 18Z. WINDS OVERNIGHT
BECOME NORTHEAST AT AROUND 5 KT OR LESS, THEN BECOME NORTHERLY THIS
AFTERNOON 5-10 KT WITH A FEW GUSTS TO 20 KT.
KSEA...VFR GENERALLY EXPECTED THROUGH THE TAF PERIOD, WITH A 10-20%
CHANCE OF AN MVFR BRIEFLY FROM 15-18Z. WINDS THIS AFTERNOON AND
THURSDAY AFTERNOON ARE OUT OF THE NORTH 5-10 KT, WITH GUSTS TO 20 KT
MORE LIKELY THURSDAY AFTERNOON. OVERNIGHT, WINDS WILL TURN NORTHEAST
AT 5 KT.
HPR
MARINE
HIGH PRESSURE AT THE SURFACE WILL REMAIN OVER THE WATERS, WITH LOWER
PRESSURE INLAND KEEPING THE PATTERN ONSHORE THROUGH MOST OF THE
WEEKEND. FLOW OVER THE COASTAL WATERS WILL CONTINUE TO REMAIN STRONG
OVER THE COASTAL WATERS, WITH GUSTY NORTHWESTERLY WINDS CONTINUING
THROUGH THE OUTER COASTAL WATERS WITH GUSTS OF UP TO 30 KT THROUGH
THURSDAY. THE WINDS WILL DECREASE ON THURSDAY, BEFORE INCREASING
AGAIN IN THE OUTER COASTAL WATERS LATE THURSDAY THROUGH SATURDAY,
WITH WINDS UP TO 25 KT. DIURNAL PUSHES THROUGH THE STRAIT OF JUAN DE
FUCA WILL CONTINUE, BUT LIKELIHOOD OF THEM REACHING 20 KT OR GREATER
REMAINS LOW.
SEAS WILL REMAIN AT 9 TO 10 FT, AND DECREASE TO 6-8 FT IN THE INNER
COASTAL WATERS THURSDAY THROUGH SATURDAY. THE OUTER COASTAL WATERS
WILL SEE SEAS DECREASE TO 6-8 FT SUNDAY THROUGH NEXT WEEK.
HPR
FIRE WEATHER
ONSHORE FLOW WILL CONTINUE TO KEEP RELATIVE HUMIDITIES MOIST THROUGH
TODAY AND THURSDAY. TEMPERATURES WILL WARM INTO THE MID 80S ON
FRIDAY, WITH RH VALUES DIPPING INTO THE LOW 30S, AND MID 20S IN THE
CASCADE FOOTHILLS. THERE IS A COOLDOWN GOING INTO SATURDAY, WITH
IMPROVED RH VALUES. THE PATTERN WARMS SIGNIFICANTLY GOING INTO
MONDAY AND TUESDAY, WITH HIGHS INTO THE 90S FOR PORTIONS OF WESTERN
WA. WIDESPREAD RH VALUES INTO THE MID AND LOW 20S (POTENTIALLY THE
TEENS) ARE EXPECTED FOR PORTIONS OF THE SOUTH PUGET SOUND/SOUTH
INTERIOR, AND PORTIONS OF THE CASCADE VALLEYS. WINDS ONLY BECOME
BREEZY IN THE AFTERNOONS EARLY NEXT WEEK FOR THE SOUTH CASCADES,
WITH WEST WINDS 5-10 MPH AND POTENTIAL FOR GUSTS TO 20 MPH. FUELS
WILL CONTINUE TO DRY AND THE ATMOSPHERE MAY BECOME CONDITIONALLY
UNSTABLE WITH A THERMAL TROUGH MOVING ALONG THE COAST MONDAY AND
TUESDAY UNDER A RIDGE.
HPR
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...SMALL CRAFT ADVISORY UNTIL 11 PM PDT THURSDAY FOR COASTAL
WATERS FROM CAPE FLATTERY TO JAMES ISLAND 10 TO 60 NM-
COASTAL WATERS FROM CAPE FLATTERY TO JAMES ISLAND OUT 10
NM-COASTAL WATERS FROM JAMES ISLAND TO POINT GRENVILLE 10
TO 60 NM-COASTAL WATERS FROM JAMES ISLAND TO POINT
GRENVILLE OUT 10 NM-COASTAL WATERS FROM POINT GRENVILLE
TO CAPE SHOALWATER 10 TO 60 NM-COASTAL WATERS FROM POINT
GRENVILLE TO CAPE SHOALWATER OUT 10 NM.
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