529
FXUS66 KSEW 170240
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
740 PM PDT SUN AUG 16 2026
SYNOPSIS
THE THUNDERSTORM THREAT WILL WIDELY DIMINISH TODAY, OUTSIDE OF A
LINGERING THREAT ACROSS THE NORTH CASCADES THIS AFTERNOON AND
EVENING. A TROUGH WILL MOVE ACROSS THE REGION LATE MONDAY INTO
TUESDAY. A WARMER AND DRIER TREND WILL COMMENCE MID TO LATE
WEEK AS A RIDGE STARTS TO BUILD INTO THE REGION, HOWEVER SHOWER
AND THUNDERSTORM CHANCES INCREASE AGAIN HEADING INTO NEXT WEEKEND
AS THE NEXT SYSTEM APPROACHES THE REGION.
SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/
FORECAST IS ON TRACK FOR THE EVENING UPDATE. -HPR
BROAD TROUGHING RESIDES OVER THE NORTHEASTERN PACIFIC THIS
AFTERNOON, WHILE UPPER LEVEL RIDGING STARTS TO NUDGE INTO THE
PACIFIC NORTHWEST FROM THE SOUTHEAST. LATEST SATELLITE IMAGERY
SHOWS SOME HIGH CLOUD COVER STILL STREAMING OVERHEAD ACROSS
WESTERN WASHINGTON THIS AFTERNOON, ALONG WITH MARINE STRATUS
SCATTERING OUT ACROSS THE INTERIOR LOWLANDS. IT ALSO SHOWS SOME
CUMULUS STARTING TO DEVELOP ALONG THE CASCADE CREST. WHILE THE
OVERALL THREAT FOR THUNDERSTORMS CONTINUES TO DIMINISH, A 15-25
PERCENT CHANCE OF THUNDERSTORMS DOES REMAIN POSSIBLE FOR THE
NORTH CASCADES THIS AFTERNOON AND EVENING. THUNDERSTORM CHANCES
WILL WANE HEADING INTO TONIGHT. ELSEWHERE ACROSS WESTERN WASHINGTON,
EXPECT DRY CONDITIONS TO CONTINUE WITH AFTERNOON HIGHS IN THE
UPPER 70S TO LOW 80S ACROSS THE INTERIOR AND IN THE MID 60S TO
LOW 70S ALONG THE COAST.
A RATHER TYPICAL SUMMERTIME PATTERN CONSISTING OF ONSHORE LOW-
LEVEL FLOW WILL CONTINUE ON MONDAY AND TUESDAY. ONSHORE FLOW
WILL BRING MORNING CLOUDS INTO PORTIONS OF THE INTERIOR, WHICH
WILL SCATTER BY THE AFTERNOON FOR SOME SUN. A TROUGH WILL PASS
THROUGH THE AREA MONDAY NIGHT INTO TUESDAY, THOUGH CONDITIONS
ARE EXPECTED TO REMAIN DRY ACROSS WESTERN WASHINGTON. HIGHS WILL
BE RATHER SEASONABLE, TOPPING OUT IN THE MID 70S TO LOWER 80S
ACROSS THE INTERIOR LOWLANDS AND IN THE 60S TO NEAR 70 ALONG THE
COAST. OVERNIGHT LOWS WILL BE IN THE 50S AREAWIDE.
LONG TERM /WEDNESDAY THROUGH SUNDAY/
ENSEMBLE GUIDANCE SUGGEST NEAR NORMAL TEMPERATURES AND ONSHORE FLOW
AT THE LOW LEVELS MAINTAINING MORNING CLOUDS WITH AFTERNOON CLEARING
FOR THE MIDWEEK TIME PERIOD. DRY CONDITIONS LIKELY CONTINUE THROUGH
THE END OF THE WEEK. AROUND FRIDAY, EXPECT THAT THE RIDGE OVER THE
ROCKIES/GREAT BASIN AMPLIFIES WITH THE NEXT UPPER TROUGH APPROACHING
THE WEST COAST. THIS WILL LIKELY BRING A SHIFT IN THE PATTERN WITH
THE POTENTIAL FOR PRECIPITATION AND COOLER TEMPERATURES, ALONG WITH
THUNDERSTORM CHANCES INCREASING INTO SATURDAY.
AVIATION
A NORTHEAST-ORIENTED TROUGH WILL DRAG SOUTHWARD, WITH NEUTRAL FLOW
ALOFT TRANSITIONING TO WEAK NORTH FLOW. SURFACE WINDS GENERALLY FROM
THE NORTH OR NORTHWEST...WITH A HANDFUL OF OBS LEANING MORE
WESTERLY. SPEEDS GENERALLY 5-10 KTS. LIGHT AND VARIABLE WINDS LESS
THAN 5 KTS EXPECTED AT MOST TERMINALS OVERNIGHT, ALTHOUGH EASTERN
PUGET SOUND TERMINALS /SEA, BFI, PAE/ WILL FAVOR MORE NORTHERLY
WINDS WITH SIMILAR SPEEDS. MOST TERMINALS RETURN TO NORTH TO
NORTHWESTERLY WINDS BY LATE MORNING/EARLY AFTERNOON WITH SPEEDS
GENERALLY 4-8 KTS.
WIDESPREAD VFR CONDITIONS OVER W WA THIS EVENING ALTHOUGH SOME
COASTAL SITES STILL TRAPPED UNDER MARINE STRATUS, HANGING ON TO MVFR
CONDITIONS. ANOTHER MARINE PUSH IS LIKELY OVERNIGHT INTO MONDAY
MORNING. CONSISTENCY OF THE STRATUS WEST OF PUGET SOUND IS LIKELY TO
CONSIST OF IFR OR LIFR CEILINGS, WITH MORE LIKELIHOOD OF LOWER
VISIBILITIES ALONG THE COAST AND STRAIT OF JUAN DE FUCA. THERE IS
SOME UNCERTAINTY WITH HOW FAR THE LOWER CEILINGS WILL TRACK INTO
PUGET SOUND, BUT PAINE FIELD HAS THE BEST CHANCE (20-30%) OF SEEING
IFR/LIFR IN THE MORNING. VFR CONDITIONS EXPECTED TO RETURN AROUND 18-
21Z MONDAY.
KSEA...VFR CONDITIONS THIS EVENING, WITH WEST WINDS AROUND 5 KT
BECOMING NORTH TO NORTHEAST UNDER 5 KT TONIGHT AND OVERNIGHT. SOME
UNCERTAINTY REMAINS AGAIN WITH HOW LOW THE STRATUS WILL GET AT THE
TERMINAL WITH THE MODELS, BUT MVFR CEILING PROBABILITY REMAINS
HIGHEST AT 30%, WITH IFR NOT FAR BEHIND AT 20%.
HPR/18
MARINE
HIGH PRESSURE CONTINUES TO BUILD OFFSHORE EARLY THIS WEEK,
STRENGTHENING OVER THE NEXT FEW DAYS. ONSHORE FLOW THROUGH THE
STRAIT OF JUAN DE FUCA EACH AFTERNOON AND EVENING WILL GENERALLY
WEAKEN THROUGH THE NEXT FEW DAYS. HAVE MAINTAINED THE EXISTING
ADVISORY FOR THE CENTRAL AND EASTERN STRAIT WITH AN EYE TOWARD
FREQUENT GUSTS TONIGHT, BUT CHANCES FOR ADDITIONAL ADVISORIES IN THE
STRAIT EARLY THIS WEEK ARE GENERALLY BELOW 40%. AS THE HIGH PRESSURE
BUILDS, EXPECT PERSISTENT NORTHWESTERLY WINDS OVER THE COASTAL WATERS
TO BUILD STEEP SEAS, REACHING AROUND 6-7 FT WITH A DOMINANT PERIOD
AROUND 7 SECONDS. THE NEXT STRONGER SYSTEM MAY APPROACH THE WATERS
LATE IN THE WEEK.
FIRE WEATHER
LOCALIZED ELEVATED FIRE WEATHER CONDITIONS CONTINUE THIS
EVENING, PRIMARILY ALONG THE NORTH CASCADES, WHERE THERE IS
ISOLATED CONVECTION MOVING OUT TO THE NORTHEAST. ONSHORE FLOW
AND EXCELLENT OVERNIGHT HUMIDITY RECOVERIES WILL HELP MITIGATE
FIRE WEATHER CONDITIONS ACROSS WESTERN WASHINGTON THROUGH THE
FIRST HALF OF THE WEEK BEFORE A WARMING AND DRYING TREND
COMMENCES MID TO LATE WEEK.
WHILE SOME UNCERTAINTY REMAINS IN THE LONG TERM PATTERN, GUIDANCE
CONTINUES TO SUGGEST THAT THE NEXT STORM SYSTEM WILL ARRIVE BY
THE WEEKEND, INCREASING THE CHANCES FOR SHOWER AND THUNDERSTORM
ACTIVITY ACROSS THE AREA AND POTENTIALLY RESULTING IN THE RETURN
TO ELEVATED TO CRITICAL FIRE WEATHER CONDITIONS.
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...SMALL CRAFT ADVISORY UNTIL 3 AM PDT MONDAY FOR CENTRAL U.S.
WATERS STRAIT OF JUAN DE FUCA-EAST ENTRANCE U.S. WATERS
STRAIT OF JUAN DE FUCA.
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