401
FXUS66 KSEW 190438
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
938 PM PDT THU JUN 18 2026
SYNOPSIS
THE PATTERN REMAINS VERY DRY ACROSS WESTERN WASHINGTON
FOR THE NEXT SEVEN DAYS. A WEAK RIDGE WILL PASS OVERHEAD ON FRIDAY
WITH SLIGHTLY WARMER TEMPERATURES. A WEAK TROUGH WILL FOLLOW ON
SATURDAY, WITH SLIGHTLY COOLER TEMPERATURES. A LARGER RIDGE OFFSHORE
WILL AMPLIFY OVER THE WEEKEND, AND MOVE OVER WESTERN WASHINGTON
EARLY NEXT WEEK. HIGHS IN THE 80S AND 90S WITH MODERATE HEATRISK
REMAINS LIKELY, WITH ELEVATED FIRE WEATHER CONCERNS DUE TO DRY
RELATIVE HUMIDITY VALUES.
SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/
IT'S A NEAR CRYSTAL CLEAR AFTERNOON ACROSS WESTERN WASHINGTON ON THE
SATELLITE, WITH JUST A COUPLE CIRRUS CLOUDS. THE SYNOPTIC PICTURE
REMAINS RELATIVELY THE SAME FROM THE PAST FEW DAYS, WITH A LARGE JET
STREAK/STREAM OVER THE NORTHERN UNITED STATES UNDER AN UPPER LOW IN
MANITOBA/ONTARIO. WASHINGTON REMAINS ON THE RIGHT ENTRY REGION OF
THE JET STREAM, SO IN TURN THE WEATHER PATTERN REMAINS DRY WITH THE
SINKING MOTION ASSOCIATED WITH THIS REGION OF THE JET. HIGHS FOR
THURSDAY REMAIN ON TRACK TO CLIMB INTO THE 70S, WITH A FEW 80S IN
THE SOUTH INTERIOR. WINDS REMAIN OUT OF THE NORTH AT AROUND 5 TO 10
MPH WITH A FEW GUSTS UP TO 20 MPH THIS AFTERNOON IN PUGET SOUND.
LOWS TONIGHT WILL DROP INTO THE MID 50S.
A WEAK RIDGE WILL PASS OVERHEAD ON FRIDAY, WITH A SLIGHT WARMUP FROM
THURSDAY. HIGHS WILL STILL RANGE IN THE 70S AND 80S, WITH A FEW MORE
80S IN PUGET SOUND/SLOPES OF THE CASCADES. WHILE HEATRISK WILL
LARGELY REMAIN MINOR FOR THE REGION, A FEW AREAS IN METRO SEATTLE
AWAY FROM THE WATER (PARTICULARLY FROM BELLEVUE TO TACOMA AND DOWN
TO OLYMPIA) WILL HAVE A 60-80% RISK OF SEEING ISOLATED AREAS OF
MODERATE HEATRISK. A TROUGH WILL PASS TO THE NORTH LATE FRIDAY INTO
SATURDAY. THIS TROUGH WILL PASS THROUGH DRY, ALTHOUGH CLOUD COVERAGE
WILL INCREASE OVERNIGHT FRIDAY INTO SATURDAY, AND ALSO RESULT IN
OVERNIGHT TEMPERATURES IN THE MID 50S. THE CLOUDS SATURDAY MORNING
WILL COOL THE HIGH TEMPERATURES, WITH HIGHS IN THE 60S AND 70S.
EXPECT WINDS TO TURN TO THE SOUTHWEST WITH A FEW GUSTS UP TO 25 MPH
IN THE SOUTH INTERIOR DURING THE OVERNIGHT PERIOD. THE CASCADES
CREST ALSO HAS THE POTENTIAL FOR A FEW GUSTS FROM THE WEST UP TO 20
MPH.
LONG TERM /SUNDAY THROUGH THURSDAY/
ENSEMBLES ARE LOCKED IN ON A RIDGE AMPLIFYING OFFSHORE THE
WASHINGTON COASTLINE SUNDAY, AS IT GETS SANDWICHED IN BETWEEN
TWO UPPER LEVEL LOWS IN THE GULF OF ALASKA, AND FAR NORTHERN
ALBERTA. THIS RIDGE WILL SHIFT INLAND ON MONDAY, AND MOVE OUT OF
THE AREA ON TUESDAY. A THERMAL TROUGH IS ALSO EXPECTED TO BUILD
ALONG THE COAST SUNDAY, SHIFTING INLAND TUESDAY INTO WEDNESDAY.
THIS PATTERN IS QUITE SIMILAR TO THE COUPLE WARM DAYS PREVIOUSLY
SEEN THE PAST SUNDAY AND MONDAY ACROSS THE STATE. AS SUCH, A
BRIEF WARM SPELL IS IN THE FORECAST IN THIS PERIOD, WITH
TEMPERATURES PEAKING ON MONDAY AND TUESDAY. THERE REMAINS
SOMEWHAT OF A TEMPERATURE SPREAD, BUT MEAN HIGHS HAVE
TEMPERATURES PEAKING INTO THE 80S AND 90S, WITH THE WARMEST
TEMPERATURES IN PUGET SOUND AREAS AWAY FROM THE WATER, THROUGH
THE CHEHALIS VALLEY AND SOUTHWEST INTERIOR. A COUPLE INSTANCES
OF 100 CAN'T BE RULED OUT EITHER FOR AREAS WEST OF OLYMPIA.
OVERNIGHT TEMPERATURES AGAIN WILL BE WARMEST IN THE SEATTLE
METRO, WITH TEMPERATURES ONLY DROPPING INTO THE LOW 60S
(EVERYWHERE ELSE WILL LIKELY SEE MID AND UPPER 50S). HEATRISK ON
MONDAY AND TUESDAY WILL LIKELY BE MODERATE FOR THOSE IN LOWLAND
OR MOUNTAIN VALLEY AREAS, WITH SEATTLE SOUTHWARD THROUGH
TACOMA/OLYMPIA HAVING A 20-30% CHANCE OF MAJOR HEATRISK. DUE TO
DRY RELATIVE HUMIDITY VALUES WITH THE LIGHT OFFSHORE PATTERN,
LOW RELATIVE HUMIDITY VALUES WILL PRODUCE ELEVATED FIRE CONCERNS
(SEE FIRE DISCUSSION BELOW).
THERE ARE SOME MODEL DISCREPANCIES AS TO HOW QUICKLY THE REGION
COOLS OFF AS THE RIDGE MOVES INLAND. THE IMMEDIATE WASHINGTON
COAST WILL SEE QUICK RELIEF WITH THE RETURN OF ONSHORE FLOW, BUT
THE INTERIOR MAY TAKE AN EXTRA DAY TO COOL OFF, AS THERE IS A
DESCENT SPREAD IN THE HIGH TEMPERATURES ON WEDNESDAY. IF THE
HIGH TEMPERATURES REMAIN IN THE MID 80S IN THE INTERIOR, THE
SEATTLE METRO MAY SEE ANOTHER DAY OF SOLID MODERATE HEATRISK.
THE TEMPERATURES CONTINUE TO COOL INTO THURSDAY, WITH HEATRISK
REDUCING TO MINOR, AND MOST AREAS OUT OF THE 80S, AND INTO THE
70S.
HPR
AVIATION
NORTHWEST FLOW ALOFT WITH VFR CONDITIONS UNDER MOSTLY CLEAR
SKIES ACROSS WESTERN WASHINGTON THIS EVENING. WINDS TURN TO THE
NORTHEAST OVERNIGHT AND EASE. IFR PROBABILITIES REMAIN HIGHEST
ALONG THE IMMEDIATE WASHINGTON COASTLINE AND SOUTH CASCADES
FRIDAY MORNING WITH PROBABILITIES FOR CEILINGS ELSEWHERE
REMAINING VERY LOW. ANY LOW CEILINGS WILL DISSIPATE BY AROUND
18Z, FOR VFR REGIONWIDE FRIDAY. WINDS WILL TURN NORTHWEST AGAIN
FRIDAY AFTERNOON AND EVENING AT 6 TO 12 KT, WITH A FEW POTENTIAL
GUSTS TO 20 KT IN THE PUGET SOUND.
KSEA...VFR THROUGH THE TAF PERIOD. WINDS TURN NORTHEAST AROUND
5 KT OVERNIGHT, BUT WINDS FRIDAY AFTERNOON OUT OF THE NORTHWEST
8-12 KT GUSTING TO 20 KT.
MARINE
HIGH PRESSURE REMAINS CENTERED OFFSHORE OVER THE PACIFIC. STRONG
NORTHWEST FLOW CONTINUES IN THE OUTER COASTAL WATERS, WITH A
TROUGH MOVING INTO SOUTHERN B.C. FRIDAY BEHIND A WEAK RIDGE.
WINDS AND SEAS IN THE INNER COASTAL WATERS HAVE DROPPED DURING
THE DAY (BASED ON BUOY OBSERVATIONS). THE LATEST SMALL CRAFT
ADVISORY UPDATE FOR THE INNER COASTAL WATERS CANCELS THE INNER
COASTAL ZONE, WITH THE SEGMENT FOR THE OUTER COASTAL ZONES
CONTINUING THROUGH FRIDAY NIGHT. WINDS UP TO 20 TO 30 KT, AND
SEAS OF 9 TO 12 FT REMAIN LIKELY IN THE OUTER COASTAL WATERS
THROUGH SATURDAY, AS THE LARGER RIDGE OFFSHORE BEGINS TO AMPLIFY
AND MOVE INLAND. A THERMAL TROUGH WILL ALSO BUILD ALONG THE
COASTLINE, RESULTING IN WEAK NORTH TO OFFSHORE FLOW GOING INTO
EARLY NEXT WEEK. ONCE THE RIDGE AND THERMAL TROUGH MOVE INLAND,
ONSHORE TO NORTHWEST FLOW WILL RETURN WITH STRONGER WINDS FOR
THE OUTER COASTAL WATERS, AND THE STRAIT OF JUAN DE FUCA.
SEAS WILL CONTINUE TO DROP FROM 8 TO 11 FT TODAY TO 6 TO 8 FT
SATURDAY, AND 4 TO 6 FT SUNDAY THROUGH TUESDAY BEFORE BUILDING
TO 6 TO 8 FT BRIEFLY TUESDAY.
HPR
FIRE WEATHER
ELEVATED FIRE WEATHER CONCERNS REMAIN FOR FRIDAY AND AGAIN
MONDAY AND TUESDAY WITH MINIMUM RELATIVE HUMIDITY VALUES
DROPPING INTO THE 30S. IN SOME LOCATIONS MONDAY AND TUESDAY,
MINIMUM RH VALUES WILL BE AS LOW AS THE 20S AND TEENS. FUELS
WILL CONTINUE TO DRY AND THE ATMOSPHERE MAY BECOME CONDITIONALLY
UNSTABLE WITH THE SURFACE THERMAL TROUGH MONDAY AND TUESDAY.
EVEN THOUGH THE FUELS HAVE NOT REACHED CRITICAL LEVELS, FINE
FUELS LIKE GRASS AND BRUSH WILL IGNITE QUICKLY WITH IT BEING SO
DRY. FELTON/HPR
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...SMALL CRAFT ADVISORY UNTIL 5 AM PDT SATURDAY FOR COASTAL
WATERS FROM CAPE FLATTERY TO JAMES ISLAND 10 TO 60 NM-
COASTAL WATERS FROM JAMES ISLAND TO POINT GRENVILLE 10 TO
60 NM-COASTAL WATERS FROM POINT GRENVILLE TO CAPE
SHOALWATER 10 TO 60 NM.
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