223
FXUS66 KSEW 161003
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
303 AM PDT SUN AUG 16 2026
SYNOPSIS
THE THUNDERSTORM THREAT WILL WIDELY DIMINISH ON SUNDAY. ANOTHER
TROUGH WILL MOVE ACROSS THE REGION LATE MONDAY INTO TUESDAY. A
WARMER AND DRIER TREND IS THEN EXPECTED MID TO LATE WEEK AS A
RIDGE STARTS TO BUILD INTO THE REGION, HOWEVER SHOWER CHANCES
MAY INCREASE AGAIN BY FRIDAY AND INTO SATURDAY AS A DISTURBANCE
APPROACHES FROM THE WEST.
SHORT TERM /TODAY THROUGH TUESDAY/
BROAD TROUGHING REMAINS OVER THE NE PAC WHILE VAST RIDGING
RESIDES UPSTREAM, NOSING INTO THE PNW TODAY. MARINE STRATUS
AGAIN FILLING UP ACROSS W WA AS MID-HIGH LEVEL CLOUDS TRACK
OVERHEAD SO FAR THIS MORNING. A CHANCE (15-25%) OF THUNDERSTORMS
IS FORECAST FOR THE NORTH CASCADES WITH LESSER PROBABILITIES
ELSEWHERE GIVEN NBM PROB THUNDER. MONDAY'S FORECAST IS QUITE
SIMILAR IN REGARDS TO CONVECTION BUT PROBABILITIES SHOULD REMAIN
CAPPED AT 10-15%, LIKELY DUE TO MORE LARGE-SCALE SUBSIDENCE
PROVIDED BY MORE PRONOUNCED RIDGING OVERHEAD. HIGHS FOR SUNDAY
AND MONDAY IN THE MID 70S TO MID 80S WITH OVERNIGHT LOWS IN THE
LOWER TO UPPER 50S. COASTAL AREA HIGHS ARE FORECAST IN THE 60S.
A RATHER TYPICAL PATTERN OF ONSHORE LOW-LEVEL FLOW MAINTAINING
MORNING CLOUDS, WITH SOME CLEARING IN THE AFTERNOON ON TUESDAY.
A PASSING TROUGH COULD PROVIDE A REINFORCING PUSH OF CLOUDS AND
KNOCK TEMPERATURES DOWN A FEW DEGREES, MAINLY FOR THE SW
INTERIOR. OTHERWISE, BENIGN CONDITIONS ARE IN STORE WITH HIGHS
IN THE MID 70S TO LOWER 80S ACROSS THE INTERIOR AND 60S ALONG
THE COAST. OVERNIGHT LOWS ARE FORECAST INTO THE 50S AREA WIDE.
LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/
AN UPPER-RIDGE LOOKS TO BUILD ACROSS THE REGION DURING THE
SECOND HALF OF THE WEEK. CONTINUED LOW-LEVEL ONSHORE FLOW WILL
HELP TO KEEP TEMPERATURES FROM WARMING TOO AGGRESSIVELY. THE
PATTERN WILL THEN BEGIN TO CHANGE TOWARDS FRIDAY AND SATURDAY AS
ENSEMBLE GUIDANCE SUGGESTS THE NEXT DISTURBANCE MAY GET CLOSE
ENOUGH TO BRING ANOTHER ROUND OF SHOWER AND POTENTIAL
THUNDERSTORM CHANCES. AND WITH THAT, TEMPERATURES COULD COOL
BELOW AVERAGE FOR THE FIRST TIME IN A WHILE.
AVIATION
THE UPPER LEVEL TROUGH OVER SOUTHWESTERN B.C. WILL RETROGRADE
OFFSHORE BUT MAINTAIN SOUTHWESTERLY FLOW ACROSS THE AREA. LOW TO MID
LEVEL STRATUS HAS DEVELOPED ACROSS MOST OF WESTERN WASHINGTON EARLY
THIS MORNING. MUCH OF SOUTHWEST WASHINGTON IS UNDER MVFR CEILINGS,
THROUGH EXPECT AREAS NORTHWARD TO EVENTUALLY SEE A LOWERING TO MVFR
THROUGH THE EARLY MORNING HOURS. PROBABILITIES ARE VERY LOW (10% OR
LESS) FOR ANY OF THE TAF SITES TO SEE IFR OR LOWER CEILINGS. STRATUS
SHOULD SLOWLY SCATTER IN THE LATE MORNING HOURS, SCATTERING BETWEEN
AROUND 19-21Z. STRATUS WILL LIKELY REMAIN IN PLACE ALONG THE
IMMEDIATE COAST AND SET THE STAGE FOR A MORE TRADITIONAL MARINE PUSH
LATE TONIGHT INTO MONDAY MORNING. LIGHT SOUTHWEST TO WEST WINDS
PREVAIL THIS MORNING, INCREASING IN THE AFTERNOON TO AROUND 5-10 KT.
WINDS THROUGH THE PUGET SOUND WILL SHIFT TO NORTHERLY BY AROUND 19-
21Z AND THROUGH THE EVENING.
KSEA...CEILINGS WILL CONTINUE TO LOWER THIS MORNING TO MVFR THROUGH
MUCH OF THIS MORNING. PROBABILITIES ARE VERY LOW (<8%) FOR IFR OR
LOWER CONDITIONS. STRATUS SHOULD BEGIN TO LIFT AND SCATTER TO VFR
AFTER 19-20Z WITH DECREASING CLOUDS THROUGH THIS EVENING. STRATUS IS
EXPECTED TO RETURN AGAIN AFTER 12Z MONDAY.
SOUTHWEST WINDS 5-8 KT WILL CONTINUE THROUGH THIS MORNING, TURNING
TO BECOME MORE NORTHWESTERLY AFTER AROUND 19-21Z AND PERSIST THROUGH
THIS EVENING. 62
MARINE
BROAD HIGH PRESSURE WILL REDEVELOP OVER THE FAR OFFSHORE WATERS
TODAY AND STRENGTHEN GOING INTO NEXT WEEK, MAINTAINING NORTHWESTERLY
WINDS OVER THE COASTAL WATERS. SEAS LOOK TO RISE TO AROUND 4-6 FT
TONIGHT. SEAS THEN LOOK TO BECOME STEEPER MONDAY NIGHT INTO TUESDAY
TO AROUND 6-8 FT AT 7 SECONDS AS WINDS INCREASE OVER THE OUTERMOST
COASTAL WATERS. STEEP SEAS LOOK TO CONTINUE THROUGH THURSDAY.
DIURNALLY DRIVEN WESTERLY WINDS WILL CONTINUE TO OCCUR EACH
AFTERNOON AND EVENING THROUGH THE STRAIT OF JUAN DE FUCA. THE
STRONGEST PUSH LOOKS TO BE TONIGHT, FOR WHICH A SMALL CRAFT ADVISORY
HAS BEEN ISSUED. THE WESTERLY PUSHES WILL GRADUALLY WEAKEN THROUGH
THE WEEK WITH ADDITIONAL HEADLINES UNLIKELY AT THIS TIME. 62/29
FIRE WEATHER
CONVECTION WILL BE LARGELY CONFINED TO NORTHERN CASCADE CREST
WHERE A 15-20% CHANCE OF THUNDERSTORM IS IN THE FORECAST
ACCORDING TO THE NBM. CONTINUED ONSHORE FLOW AND EXCELLENT
OVERNIGHT HUMIDITY RECOVERIES WILL THEN HELP MITIGATE FIRE
WEATHER CONDITIONS TO START THE WEEK. WHILE SOME UNCERTAINTY
REMAINS IN THE LONG TERM PATTERN, ENSEMBLE GUIDANCE HAS
INCREASINGLY COME TO CONSENSUS THAT A WARMING AND DRYING TREND
IS LIKELY MID TO LATE WEEK, BEFORE THE POTENTIAL FOR SHOWER AND
THUNDERSTORM CHANCES INCREASES AGAIN LATE WEEK AS THE NEXT
DISTURBANCE APPROACHES FROM THE WEST. THIS COULD POTENTIALLY
REINTRODUCE SOME ELEVATED FIRE WEATHER CONCERNS TO THE AREA.
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...SMALL CRAFT ADVISORY UNTIL 5 AM PDT EARLY THIS MORNING FOR
CENTRAL U.S. WATERS STRAIT OF JUAN DE FUCA-EAST ENTRANCE
U.S. WATERS STRAIT OF JUAN DE FUCA.
SMALL CRAFT ADVISORY FROM 4 PM THIS AFTERNOON TO 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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