448
FXUS66 KSEW 151638
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
938 AM PDT SAT AUG 15 2026
SYNOPSIS
THUNDERSTORM POTENTIAL WILL CONTINUE ALONG THE CASCADES
TODAY, BUT WILL WANE THROUGHOUT THE WEEKEND AS AN UPPER LEVEL
RIDGE STARTS TO BUILDS INTO THE AREA FROM THE SOUTHEAST. ANOTHER
UPPER LEVEL TROUGH WILL MOVE INTO THE REGION EARLY NEXT WEEK.
UNCERTAINTY THEN INCREASES IN THE FORECAST HEADING INTO MIDWEEK
AS GUIDANCE REMAINS SPLIT BETWEEN A WARMER, DRIER PATTERN AND A
COOLER, WETTER ONE.
SHORT TERM /TODAY THROUGH MONDAY/
BROAD UPPER-TROUGHING RESIDES OVER THE PAC COAST THIS MORNING
WHILE UPPER-RIDGING IS POSITIONED ACROSS MUCH OF THE NATION.
IN THE PNW, A WEAK UPPER-LOW WILL INFLUENCE THE WEATHER TODAY AS
THE MAIN HIGHLIGHT ONCE AGAIN IS SHOWERS AND THUNDERSTORMS
FORECASTED FOR THE MOUNTAINS. AS A RESULT, ELEVATED FIRE
WEATHER CONDITIONS ARE EXPECTED FOR THE CASCADES.
MARINE STRATUS HAS MARCHED WELL INLAND THIS MORNING -STRETCHING
FROM THE COAST INTO PUGET SOUND. IT'LL REMAIN IN PLACE BEFORE
GRADUALLY BURNING OFF INTO THE AFTERNOON. HOWEVER, AFOREMENTIONED
THUNDERSTORMS WILL POTENTIALLY EMERGE THIS AFTERNOON ALONG THE
CASCADE CREST AS A SUBTLE SHORTWAVE WITHIN THE MEAN FLOW TRACKS
INTO THE REGION AND PERTURBS THE ENVIRONMENT. LATEST HREF
DEPICTS 500-800 J/KG OF SURFACE CAPE ALONG THE CASCADES WITH
250-500 J/KG ACROSS THE OLYMPICS. MODEL DERIVED 700-500 MB LAPSE
RATES ARE AROUND 6 C/KM, CONDITIONALLY UNSTABLE FOR ANY SATURATED
AIR PARCELS. THE NBM HAS A 20-30% CHANCE OF THUNDERSTORMS THIS
AFTERNOON INTO THE EVENING AND LESS THAN 15% ELSEWHERE ACROSS
WESTERN WASHINGTON. THE THREAT SHOULD END TONIGHT BARRING A FEW
STRAGGLERS. HIGHS TODAY FOR THE INTERIOR ARE FORECAST TO RANGE
BETWEEN THE MID 70S TO LOWER 80S. COASTAL AREAS ARE FAVORED TO
REMAIN IN THE 60S. OVERNIGHT LOWS WILL BE IN THE UPPER 40S TO
UPPER 50S.
GLOBAL GUIDANCE HAS RIDGING BUILDING INTO THE REGION OUT OF THE
SOUTHEAST ON SUNDAY. SOUTHWEST FLOW ALOFT WILL HELP PUSH SMOKE
EASTWARD AND AWAY FROM THE REGION. A SLIGHT CHANCE (15-20%) OF
THUNDERSTORMS IS FORECAST FOR THE NORTH CASCADES WITH LESSER
PROBABILITIES SOUTHWARD ALONG THE RANGE. MONDAY'S FORECAST IS
QUITE SIMILAR IN REGARDS TO CONVECTION BUT PROBABILITIES SHOULD
REMAIN CAPPED AT 15%, LIKELY DUE TO MORE LARGE-SCALE SUBSIDENCE
PROVIDED BY DIRECT RIDGING OVERHEAD. HIGHS FOR SUNDAY AND MONDAY
IN THE MID 70S TO MID 80S WITH OVERNIGHT LOWS IN THE LOWER TO
UPPER 50S. COASTAL AREAS HIGHS ARE FORECAST IN THE 60S.
LONG TERM /MONDAY NIGHT THROUGH FRIDAY/
THE FIRST PART OF NEXT WEEK REMAINS TO FOLLOW A RATHER TYPICAL
PATTERN OF ONSHORE LOW-LEVEL FLOW MAINTAINING MORNING CLOUDS, WITH
SOME CLEARING IN THE AFTERNOON. A PASSING TROUGH AROUND TUESDAY
COULD PROVIDE A REINFORCING PUSH OF CLOUDS AND KNOCK TEMPERATURES A
FEW DEGREES COOLER THAN NORMAL. OTHERWISE, ENSEMBLE GUIDANCE BEGINS
TO SPREAD A BIT LARGER TOWARD THE MIDDLE OF NEXT WEEK WITH A FAIRLY
EVEN SPLIT BETWEEN A COOLER TROUGH PATTERN AND A WARMER (NEAR NORMAL)
PATTERN UNDER ZONAL FLOW OR A WEAK RIDGE. IN ANY EVENT, THERE'S
NOT A SIGNIFICANT SIGNAL FOR ANY PRECIPITATION OF NOTE WITH
TEMPERATURES LEANING WARMER THAN AVERAGE.
AVIATION
A MIX OF CONDITIONS RANGING FROM MVFR TO LIFR THIS
MORNING ASSOCIATED WITH MARINE STRATUS. VFR CONDITIONS ARE EXPECTED
ONCE THE STRATUS DISSIPATES, BUT MODELS ARE HINTING AT A LATER CLEAR-
OUT TIMING, POTENTIALLY AS LATE AS 19-21Z ACROSS THE INTERIOR. THE
COAST WILL LIKELY NOT FULLY CLEAR OUT IN THE AFTERNOON BEFORE
STRATUS REBUILDS TONIGHT INTO SUNDAY MORNING. LIGHT WSW WINDS WILL
INCREASE IN THE AFTERNOON. WINDS LOOK TO SWITCH NW ACROSS CENTRAL
PUGET SOUND TERMINALS AFTER 00-02Z. WINDS WILL EASE LATE TONIGHT.
KSEA...SLOW IMPROVEMENT THIS MORNING TO MVFR. MODELS REMAIN
CONSISTENT WITH A LATER CLEAR OUT TIME AROUND 20Z. VFR CONDITIONS
THIS AFTERNOON WILL BE FOLLOWED BY ANOTHER ROUND OF STRATUS SUNDAY
MORNING. LATEST GUIDANCE SUGGESTS A 30% CHANCE FOR MVFR CIGS AFTER
12Z SUNDAY. WINDS PREDOMINANTLY FROM THE SW AT 4-7 KT, AND MAY
ATTEMPT TO TURN MORE W TO NW BETWEEN 02-06Z.
62/29
MARINE
HIGH PRESSURE WILL REMAIN WELL OFF THE COAST OF CALIFORNIA TODAY,
KEEPING WINDS LIGHT OVER THE COASTAL WATERS.
NORTHWESTERLY WINDS WILL BEGIN TO RESUME SUNDAY AS HIGH PRESSURE
REBUILDS OF THE COAST OF BRITISH COLUMBIA. THE HIGH WILL STRENGTHEN
AS IT SHIFTS SOUTHWARD OFF THE PACIFIC NORTHWEST COAST, MAINTAINING
NW WINDS INTO NEXT WEEK. SEAS LOOK TO REMAIN BETWEEN 3-6 FT THROUGH
NEXT WEEK.
DIURNALLY DRIVEN WESTERLY WINDS WILL CONTINUE TO OCCUR EACH
AFTERNOON AND EVENING IN THE STRAIT OF JUAN DE FUCA THROUGH THIS
WEEKEND AND INTO EARLY NEXT WEEK WITH GUSTS REACHING SMALL CRAFT
ADVISORY CRITERIA AT TIMES. THE WESTERLY PUSHES LOOK TO START TO
WEAKEN BY THE MIDDLE OF NEXT WEEK. 62
FIRE WEATHER
ELEVATED FIRE WEATHER CONDITIONS WILL CONTINUE ACROSS THE
CASCADES TODAY WITH CHANCES OF THUNDERSTORMS POSSIBLE AGAIN
ALONG THE CASCADE CREST THIS AFTERNOON AND EVENING. OVERALL
CHANCES FOR CONVECTION WILL DECREASE THROUGHOUT THE WEEKEND,
HOWEVER, AS AN UPPER LEVEL RIDGE STARTS TO BUILD INTO THE AREA
FROM THE SOUTHEAST. BY SUNDAY, EXPECT CONVECTION TO MAINLY BE
CONFINED TO THE CASCADE CREST AND AREAS EAST OF THE CREST.
ANOTHER UPPER LEVEL TROUGH WILL MOVE INTO THE AREA NEXT WEEK AND
COULD BRING SOME ADDITIONAL ELEVATED FIRE WEATHER CONCERNS TO
WESTERN WASHINGTON AT TIMES.
14/41
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...SMALL CRAFT ADVISORY FROM 2 PM THIS AFTERNOON TO 5 AM PDT
SUNDAY FOR CENTRAL U.S. WATERS STRAIT OF JUAN DE FUCA-
EAST ENTRANCE U.S. WATERS STRAIT OF JUAN DE FUCA.
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