960
FXUS66 KSEW 121024
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
324 AM PDT WED AUG 12 2026
SYNOPSIS
WEAK UPPER LEVEL TROUGH OVER THE AREA WITH LOW LEVEL ONSHORE
FLOW THROUGH FRIDAY. WEAK UPPER LEVEL RIDGE BUILDING IN FROM THE
SOUTHEAST WITH SOUTHERLY FLOW ALOFT OVER THE WEEKEND. ANOTHER
WEAK UPPER LEVEL TROUGH WILL ARRIVE MONDAY AND TUESDAY.
SHORT TERM /TODAY THROUGH FRIDAY/
SATELLITE IMAGERY SHOWS A MIX OF CLOUD COVER OVER THE AREA EARLY
THIS MORNING. NOT GOOD FOR PERSEID FANS. LOW STRATUS ALONG THE
COAST HAS ALREADY ALMOST MADE IT INTO THE PUGET SOUND AREA AT 3
AM/10Z. IN ADDITION TO THE LOW CLOUDS SOME CIRRUS MOVING
THROUGH AS WELL. TEMPERATURES WERE IN THE MID 50S TO MID 60S.
WEAK UPPER LEVEL TROUGH OVER THE AREA TODAY WITH LOW LEVEL
ONSHORE FLOW. STRATUS WILL MOVE A LITTLE MORE INLAND IN THE NEXT
COUPLE OF HOURS GETTING EAST OF THE PUGET SOUND. THE LAYER IS
SHALLOW ( THE BLACK HILLS ARES SHOWING UP ON SATELLITE IMAGERY
PUTTING THE TOPS BELOW 3000 FEET ). THIS COMBINED WITH
WEAKENING ONSHORE GRADIENTS LATER THIS MORNING THROUGH THE
AFTERNOON HOURS WILL CAUSE THE STRATUS DECK TO RETREAT BACK TO
THE COASTLINE BY EARLY AFTERNOON. UPPER LEVEL TROUGH AXIS MOVING
THROUGH THIS AFTERNOON PROVIDING JUST ENOUGH INSTABILITY FOR A
CHANCE OF SHOWERS AND A SLIGHT CHANCE OF THUNDERSTORMS OVER THE
OLYMPICS AND NORTH CASCADES. HIGH TEMPERATURES A COUPLE OF
DEGREES BELOW NORMAL, 70S INLAND AND MID TO UPPER 60S COAST.
LITTLE CHANGE IN THE PATTERN TONIGHT THROUGH FRIDAY. WEAK UPPER
LEVEL TROUGH REMAINING OVER THE AREA WITH LOW LEVEL ONSHORE
FLOW. ONSHORE FLOW INCREASING IN THE NIGHT AND EARLY MORNING
HOURS AND WEAKENING IN THE AFTERNOON. STRATUS ALONG THE COAST
MOVING INLAND OVERNIGHT REACHING THE PUGET SOUND AREA BEFORE
SUNRISE. LIKE TODAY THE MARINE LAYER WILL NOT BE DEEP ENOUGH TO
HANG AROUND INTO THE AFTERNOON HOURS FOR THE INTERIOR. JUST
ENOUGH INSTABILITY IN THE AFTERNOON TO KEEP A SLIGHT CHANCE OF
SHOWERS OR THUNDERSTORMS IN THE OLYMPICS AND CASCADES BOTH
AFTERNOONS. A TOUCH WARMER THURSDAY AND FRIDAY WITH 70S AND
LOWER 80S INLAND. HIGHS ON THE COAST REMAINING IN THE MID TO
UPPER 60S.
A BIT UNLUCKY THIS MORNING WITH THE AREA OF CIRRUS MOVING
THROUGH RIGHT AT THE PEAK TIME OF THE PERSEID METEOR SHOWER.
BETTER CHANCE TO SEE THEM INLAND LATE TONIGHT/EARLY THURSDAY
MORNING. UNFORTUNATELY THE MARINE LAYER WILL BE INTACT ALONG
THE COAST KEEPING SKIES CLOUDY IN THE OVERNIGHT HOURS. FELTON
LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/
EXTENDED MODELS IN GOOD AGREEMENT OVER THE WEEKEND WITH AN UPPER
LEVEL RIDGE WELL TO THE SOUTHEAST TRYING TO BACK BUILD INTO
WESTERN WASHINGTON. END RESULT IS JUST SOME WEAK RIDGING OVER
THE AREA WITH 500 MB HEIGHTS ONLY GETTING INTO THE LOWER 580
DMS. WILL HAVE TO KEEP AN EYE OUT ON HOW THIS PATTERN DEVELOPS.
WE COULD END UP WITH SOUTHERLY FLOW ALOFT WHICH WOULD OPEN THE
DOOR TO THE POSSIBILITY OF LATE DAY CONVECTION OVER THE
CASCADES. MODEL SOLUTIONS START TO DIVERGE MONDAY WITH THE GFS
KEEPING THE WEAK RIDGE IN PLACE WHILE THE ECMWF BRINGS ANOTHER
UPPER LEVEL TROUGH INTO THE AREA. ENSEMBLE SOLUTIONS FAVORING
THE ECMWF SO WILL HAVE A SLIGHT CHANCE OF SHOWERS IN THE
FORECAST FOR MONDAY AND TUESDAY WITH TEMPERATURES NEAR OR SLIGHT
BELOW NORMAL.
FOR THE SECOND TIME IN THE LAST THREE YEARS THERE HAS BEEN NO
MEASURABLE RAIN IN SEATTLE IN THE FIRST 11 DAYS OF AUGUST. THIS
IS NOT AS COMMON AS YOU MIGHT THINK. IN THE 82 YEARS OF RECORDS
AT SEATTLE-TACOMA AIRPORT THE FIRST 11 DAYS OF AUGUST HAVE BEEN
DRY 31 TIMES ( 38% ). OUT OF THE 31 YEARS ONLY 7 HAVE HAD ZERO
PRECIPITATION WITH THE OTHER 24 YEARS REPORTING A TRACE. FELTON
AVIATION
WESTERLY FLOW ALOFT WILL BECOME VARIABLE TONIGHT AS A SHORTWAVE
TROUGH MOVES DIRECTLY OVERHEAD WESTERN WASHINGTON. STRATUS CONTINUES
TO DEVELOP ACROSS THE WESTERN WASHINGTON INTERIOR AND SHOULD
CONTINUE TO FILL IN THROUGHOUT THE MORNING, BRINGING MVFR TO IFR
CIGS, FOR AT LEAST A BRIEF PERIOD FOR THE PUGET SOUND AREA
TERMINALS. STRATUS WILL SCATTER AND RETREAT TO THE COAST AFTER
SUNRISE AND THROUGH THE MORNING, GIVING WAY TO VFR CONDITIONS.
STRATUS MAY NOT COMPLETELY CLEAR ALONG THE IMMEDIATE COASTLINE,
SETTING THE STAGE FOR REDEVELOPMENT TONIGHT INTO EARLY THURSDAY.
OUTSIDE OF THE TERMINALS, SHOWERS AND ISOLATED THUNDERSTORMS ARE
EXPECTED TO DEVELOP OVER THE MOUNTAINS THIS AFTERNOON/EARLY EVENING,
WITH THE BEST CHANCES OVER THE OLYMPICS AND THE NORTHERN CASCADES.
LIGHT ONSHORE WINDS EARLY THIS MORNING WILL STRENGTHEN THIS
AFTERNOON. LIGHT NORTHERLY WINDS THROUGH THE PUGET SOUND LOOK TO
BRIEFLY SWITCH TO SOUTHWEST FROM 15-20Z THIS MORNING BEFORE WINDS
SWITCH BACK TO NORTHERLY IN THE AFTERNOON.
KSEA...VFR CONDITIONS ARE EXPECTED THROUGH MOST OF THE TAF PERIOD,
EXCEPT BETWEEN AROUND 12-19Z THIS MORNING AS MVFR TO IFR STRATUS
DEVELOPS NEAR THE TERMINAL. ANOTHER ROUND OF STRATUS WILL BE
POSSIBLE AGAIN EARLY THURSDAY MORNING AS WELL. LIGHT NORTHERLY WINDS
LESS THAN 5 KT WILL BRIEFLY SWING AROUND TO SOUTHWESTERLY BETWEEN
AROUND 15-19Z THIS MORNING BEFORE SWITCHING BACK TO
WEST/NORTHWESTERLY 6-8 KT THROUGH THE REMAINDER OF THE DAY. 62
MARINE
BROAD HIGH PRESSURE OVER THE NORTHEAST PACIFIC WILL SLOWLY WEAKEN
THROUGH THE WEEK AND GET PUSHED TO THE SOUTH THROUGH, ALLOWING FOR
WINDS OVER THE COASTAL WATERS TO WEAKEN FRIDAY INTO THE WEEKEND.
WESTERLY PUSHES DOWN THE STRAIT OF JUAN DE FUCA WILL CONTINUE
THROUGH THE WEEK AND INTO THIS WEEKEND. GUIDANCE IS INDICATING THAT
THIS EVENING'S PUSH LOOKS TO BE LESS STRONG WITH WEAKER GRADIENTS;
THE STRONGER WINDS WILL LIKELY BE CONFINED TO THE CANADIAN SIDE.
THUS, HAVE HELD OFF ON ISSUING A SMALL CRAFT ADVISORY FOR THE STRAIT
THIS EVENING. PROBABILITIES FOR SCA WINDS INCREASES FRIDAY THROUGH
THE WEEKEND.
SEAS 2 TO 4 FT TODAY MAY INCREASE CLOSER TO 6 FT THROUGH THE OUTER
COASTAL WATERS TONIGHT INTO THURSDAY, OTHERWISE REMAIN AROUND 2 TO 4
FT THURSDAY NIGHT THROUGH THE WEEKEND. 62
FIRE WEATHER
IN GENERAL A LOW LEVEL ONSHORE FLOW WITH TEMPERATURES NEAR
NORMAL PATTERN WOULD NOT BE CONCERNING FOR FIRE WEATHER. THE
CHANCE, 20 TO 30 PERCENT, FOR AFTERNOON CONVECTION IN THE
MOUNTAINS THE NEXT FEW DAYS FIRST WITH THE WEAK INSTABLILTY WITH
THE UPPER LEVEL TROUGH THROUGH FRIDAY THEN OVER THE WEEKEND THE
POSSIBLE SOUTHERLY FLOW ALOFT WILL KEEP FIRE WEATHER CONCERNS
ELEVATED FOR THE NEXT FEW DAYS. ANY CONVECTION THAT DOES DEVELOP
DOES NOT LOOK LIKE IT WILL BE ACCOMPANIED BY WETTING RAINS.
FELTON
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.
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