624
FXUS66 KSEW 131033
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
333 AM PDT THU AUG 13 2026
SYNOPSIS
WEAK UPPER LEVEL TROUGH OVER THE AREA THROUGH FRIDAY NIGHT. AIR
MASS SOMEWHAT UNSTABLE DURING THE AFTERNOON AND EVENING HOURS
OVER THE HIGHER TERRAIN. WEAK UPPER LEVEL RIDGE OVER THE
WEEKEND WILL BE REPLACED BY ANOTHER TROUGH MONDAY. THE TROUGH
WILL HANG OVER THE AREA THROUGH MOST OF NEXT WEEK. ONSHORE FLOW
IN THE LOWER LEVELS WILL KEEP HIGH TEMPERATURES NEAR NORMAL
THROUGH THE PERIOD.
SHORT TERM /TODAY THROUGH SATURDAY/
SATELLITE IMAGERY SHOWS STRATUS ALONG THE COAST MOVING THROUGH
THE LOWER CHEHALIS VALLEY AND DOWN THE STRAIT OF JUAN DE FUCA
EARLY THIS MORNING. CLOUDLESS SKIES OVER THE REMAINDER OF THE
AREA WITH A LAYER OF SMOKE ALOFT. TEMPERATURES AT 3 AM/10Z WERE
IN THE MID 50S TO MID 60S.
UPPER LEVEL TROUGH OVER THE AREA TODAY WILL REMAIN IN PLACE
THROUGH FRIDAY NIGHT. AIR MASS BECOMING UNSTABLE OVER THE HIGHER
TERRAIN IN THE AFTERNOON AND EARLY EVENING HOURS BOTH TODAY AND
FRIDAY. MODEL SOUNDINGS HAVE LIFTED INDEXES BELOW 0 OVER THE
CASCADES AND OLYMPICS WITH CAPE VALUES UP TO 1000 G/KG AT 00Z
THIS AFTERNOON AND AGAIN FRIDAY AFTERNOON. THE FIRE WEATHER
WATCH FOR THE OLYMPICS AND CASCADES FOR LATER TODAY WILL BE
UPGRADED TO A RED FLAG WARNING WITH THIS FORECAST PACKAGE. WHAT
CONVECTION THAT DOES DEVELOP HAS A HIGH PROBABILITY OF NOT
PRODUCING WETTING RAINS AND CREATING GUSTY AND ERRATIC OUTFLOW
WINDS NEAR THE STORM. IN THE LOWLANDS LOW LEVEL ONSHORE FLOW
WITH A SHALLOW MARINE LAYER JUST GETTING EAST OF PUGET SOUND
AFTER SUNRISE BOTH MORNINGS. THE LAYER WILL RETREAT BACK TO THE
COASTLINE BY MIDDAY. HIGHS BOTH DAYS IN THE 70S AND LOWER 80S
INLAND, MID AND UPPER 60S ALONG THE COAST. LOWS 50S AND LOWER
60S.
UPPER LEVEL TROUGH DISSIPATING FRIDAY NIGHT WITH AN UPPER LEVEL
RIDGE BACK BUILDING INTO WESTERN WASHINGTON FROM THE SOUTHEAST
SATURDAY. STILL SLIGHTLY UNSTABLE OVER THE CASCADES LATE IN THE
DAY FOR A SLIGHT CHANCE OF CONVECTION. IN THE LOWLANDS LITTLE
CHANGE WITH THE LOW LEVEL ONSHORE FLOW PATTERN REMAINING INTACT.
SHALLOW MARINE LAYER MOVING INLAND IN THE LATE NIGHT AND
MORNING HOURS WILL DISSIPATE OVER ALL BUT THE COASTLINE BY
MIDDAY. LOWS IN THE 50S AND LOWER 60S. LITTLE CHANGE IN THE
HIGHS WITH 70S AND LOWER 80S INLAND AND MID AND UPPER 60S COAST.
SMOKE ALOFT REMAINING OVER THE AREA AT LEAST THROUGH FRIDAY. A
LITTLE BIT OF MIXING WITH THE DAYTIME HEATING WILL GET SOME OF
THE SMOKE DOWN TOWARDS THE SURFACE BUT THE LOW LEVEL ONSHORE
FLOW WILL PREVENT THE SMOKE FROM GETTING TOO BAD AT THE SURFACE
THE NEXT FEW DAYS. FELTON
LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/
MODELS IN GOOD AGREEMENT WITH THE UPPER LEVEL RIDGE REMAINING
OVER THE AREA THROUGH SUNDAY NIGHT BEFORE GETTING REPLACED BY
YET ANOTHER UPPER LEVEL TROUGH MONDAY. UPPER LEVEL TROUGH
REMAINING OVER THE AREA THROUGH WEDNESDAY. LOW LEVEL ONSHORE
FLOW THROUGH THE PERIOD INCREASING MIDWEEK. AIR MASS OVER THE
HIGHER TERRAIN ONCE AGAIN BECOMING UNSTABLE LATE IN THE DAY
UNDER THE TROUGH FOR AT LEAST A SLIGHT CHANCE OF CONVECTION
MONDAY THROUGH WEDNESDAY. LITTLE CHANGE IN THE TEMPERATURES.
HIGHS 70S AND LOWER 80S INLAND WITH MID AND UPPER 60S COAST.
LOWS IN THE 50S AND LOWER 60S. INCREASING ONSHORE FLOW IN THE
MIDDLE OF NEXT WEEK COOLING HIGHS INTO THE MID 60S TO MID 70S.
FELTON
AVIATION
UPPER LEVEL TROUGHING OVERHEAD WILL KEEP WEST TO SOUTHWESTERLY FLOW
ALOFT. IFR TO LIFR STRATUS IS EVER SO SLOWLY CONTINUING TO BUILD AND
CREEP WESTWARD. EXPECT THE STRATUS TO SLOWLY BUILD AND FILL IN
THROUGH THE REST OF THE MORNING, BUT AGAIN WILL LIKELY RAISE AND
SCATTER FAIRLY QUICKLY THROUGH THE MORNING HOURS. STRATUS SHOULD
RETREAT TO THE IMMEDIATE COAST BY AROUND NOON/20Z AND CONDITIONS
REMAIN VFR UNTIL STRATUS REBUILDS AND BEGINS TO PUSH BACK EAST LATE
TONIGHT INTO FRIDAY MORNING. LIGHT ONSHORE WINDS WILL INCREASE TO
AROUND 5-10 KT LATE MORNING, WITH NORTHERLY WINDS THROUGH THE PUGET
SOUND INTERIOR. OUTSIDE OF THE MAIN TERMINALS, THERE WILL BE CHANCES
OF SHOWERS AND ISOLATED THUNDERSTORMS (25-35%) ALONG THE CASCADE
CREST, THOUGH THERE IS ALSO A LOW (10-15%) CHANCE OVER THE OLYMPICS,
AS WELL.
KSEA...VFR CONDITIONS THROUGH MOST OF THE PERIOD, THROUGH A BRIEF
PERIOD OF MVFR TO IFR CIGS BETWEEN AROUND 13-17Z AS STRATUS BUILDS
OVER THE TERMINAL. STRATUS MAY (20% CHC) REBUILD AGAIN OVER THE
TERMINAL AFTER 12Z FRI. LIGHT WINDS THIS MORNING BECOMING SW LESS
THAN 5 KT BEFORE 17Z, THEN SWITCHING TO W THAN NW THROUGH THE LATE
MORNING AND REMAIN N 5-8 KT THROUGH TONIGHT. 62
MARINE
HIGH PRESSURE IN THE NORTHEAST PACIFIC WILL WEAKEN GOING INTO THE
END OF THE WEEK AS IT GETS PUSHED SOUTH INTO THE WEEKEND BY SYSTEMS
OVER THE OPEN WATERS. DIURNAL WESTERLY PUSHES THROUGH THE STRAIT OF
JUAN DE FUCA REMAINS THE PRIMARY IMPACT, ALTHOUGH CHANCES FOR SMALL
CRAFT ADVISORY CONDITIONS REMAIN LOW UNTIL FRIDAY EVENING AND
STRONGER PUSHES WILL CONTINUE THROUGH THE WEEKEND. WINDS IN THE
COASTAL WATERS WILL DECREASE TONIGHT AS PRESSURE GRADIENTS DECREASE.
HIGH PRESSURE LOOKS TO REBUILD GOING INTO NEXT WEEK.
SEAS REMAIN 3-5 FT THROUGH THE FORECAST PERIOD. 62
FIRE WEATHER
FIRE WEATHER CONCERNS REMAIN ELEVATED TO CRITICAL AT TIMES
THROUGH FRIDAY NIGHT. UPPER LEVEL TROUGH OVER THE AREA. AIR MASS
BECOMING UNSTABLE OVER THE HIGHER TERRAIN IN THE AFTERNOON AND
EARLY EVENING HOURS CREATING A CHANCE FOR THUNDERSTORMS. THERE
IS A HIGH PROBABILITY THESE STORMS WILL NOT PRODUCE WETTING
RAINS BUT COULD PRODUCE GUSTY ERRATIC OUTFLOW WINDS. THE FIRE
WEATHER WATCH TODAY FOR THE OLYMPICS AND CASCADES WILL BE
UPGRADED TO A WARNING. IF FORECAST TRENDS CONTINUE ANOTHER FIRE
WEATHER WATCH COULD BE ISSUED FOR FRIDAY AFTERNOON AND EVENING
WITH LATER FORECAST PACKAGES.
UPPER LEVEL TROUGH REPLACED BY AN UPPER LEVEL RIDGE OVER THE
WEEKEND LESSENING BUT NOT ELIMINATING THE CHANCES FOR CONVECTION
OVER THE MOUNTAINS ESPECIALLY THE CASCADES. ANOTHER UPPER LEVEL
TROUGH MOVING INTO THE AREA NEXT WEEK WILL ONCE AGAIN INCREASE
FIRE WEATHER CONCERNS. FELTON
SEW WATCHES/WARNINGS/ADVISORIES
WA...FIRE WEATHER WATCH FROM 11 AM PDT THIS MORNING THROUGH THIS
EVENING FOR EAST PORTION OF THE OLYMPIC MOUNTAINS-WEST
PORTION OF THE OLYMPIC MOUNTAINS-WEST SLOPES OF THE
CENTRAL CASCADES GENERALLY ABOVE 1500 FEET-WEST SLOPES OF
THE NORTH CASCADES GENERALLY ABOVE 1500 FEET.
PZ...NONE.
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