069
FXUS66 KSEW 201036
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
336 AM PDT THU AUG 20 2026
SYNOPSIS
WEAK UPPER LEVEL RIDGE WITH LIGHT ONSHORE FLOW IN THE LOWER
LEVELS TODAY. UPPER LEVEL LOW APPROACHING FROM THE SOUTHWEST
FRIDAY WILL MOVE INTO THE COASTAL WATERS SATURDAY AND INTO
SOUTHERN BRITISH COLUMBIA EARLY SUNDAY MORNING. SYSTEM SPINNING
OUT OF LOW MOVING THROUGH SATURDAY WITH SHOWERS AND POSSIBLE
THUNDERSTORMS. UPPER LEVEL RIDGE REBUILDING SUNDAY WILL MOVE
EAST MONDAY. WEAK SYSTEM MOVING THROUGH LATE TUESDAY NIGHT AS AN
UPPER LEVEL TROUGH DEVELOPS WELL OFF THE COAST.
SHORT TERM /TODAY THROUGH SATURDAY/
SATELLITE IMAGERY SHOWS STRATUS ALONG THE COAST INTO THE LOWER
CHEHALIS VALLEY AND ABOUT HALF WAY DOWN THE STRAIT OF JUAN DE
FUCA. CLEAR SKIES ELSEWHERE. TEMPERATURES AT 3 AM/10Z WERE IN
THE 50S TO MID 60S.
SLIGHT CHANGE IN THE PATTERN TODAY. A LITTLE BIT WEAKER ONSHORE
FLOW HAS RESULTED IN A SHALLOWER MARINE LAYER. STRATUS WAY
BEHIND SCHEDULE VERSUS THE OTHER MORNINGS IN THE LAST WEEK
GETTING INTO SHELTON ABOUT TWO HOURS LATER THAN THE LAST FEW
DAYS. WITH THE WEAKER ONSHORE GRADIENTS STRATUS NOT GETTING EAST
OF PUGET SOUND THIS MORNING. A LITTLE MORE SUNSHINE FOR THE
INTERIOR WILL PUSH HIGH TEMPERATURES UP A COUPLE OF DEGREES WITH
HIGHS IN THE MID 70S TO MID 80S. STRATUS RETREATING OFF THE
COASTLINE THIS AFTERNOON WARMING HIGHS ALONG THE COAST INTO THE
MID 60S TO MID 70S.
CHANGES IN THE PATTERN STARTING TONIGHT. UPPER LEVEL LOW WELL TO
THE SOUTHWEST BEGINNING TO MOVE NORTHEAST. THIS IN TURN WILL
BUILD THE UPPER LEVEL RIDGE OUT AHEAD OF THE LOW OVER THE
PACIFIC NORTHWEST. FLOW ALOFT GOING SOUTHERLY TONIGHT AND
REMAINING SOUTHERLY FRIDAY AS THE LOW CONTINUES TO SLOWLY MOVE
NORTHEAST. LIGHT FLOW IN THE LOWER LEVELS WILL KEEP THE STRATUS
WEST OF PUGET SOUND AGAIN FRIDAY MORNING BUT WITH THE SOUTHERLY
FLOW ALOFT THERE WILL BE PLENTY OF MIDDLE AND HIGH LEVEL CLOUDS.
LOWS TONIGHT IN THE 50S. CLOUD COVER THICK ENOUGH FRIDAY TO
LOWER THE HIGHS A LITTLE, 70S AND LOWER 80S INLAND AND MID 60S
TO LOWER 70S COAST.
UPPER LEVEL LOW CONTINUING TO MOVE NORTHEAST FRIDAY NIGHT AND
SATURDAY ENDING UP JUST WEST OF GRAYS HARBOR BY 00Z SUNDAY.
UPPER LEVEL DISTURBANCE SPINNING OUT OF THE LOW MOVING THROUGH
WESTERN WASHINGTON SATURDAY MORNING INTO THE AFTERNOON. WITH
SOME UPPER LEVEL DIFFLUENCE AIR MASS BECOMING SOMEWHAT UNSTABLE
AS THIS FEATURE MOVES THROUGH PRODUCING SHOWERS AND A CHANCE OF
THUNDERSTORMS EVEN FOR THE LOWLANDS. BREEZY WITH AND JUST
BEHIND THE SYSTEM SATURDAY. LOWS FRIDAY NIGHT IN THE MID 50S TO
LOWER 60S. HIGHS SATURDAY MUCH COOLER WITH THE CONVECTIVE
ACTIVITY, IN THE 60S AND LOWER 70S. FELTON
LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/
UPPER LEVEL LOW MOVING INTO SOUTHERN BRITISH COLUMBIA BY 12Z
SUNDAY WITH SHOWER ACTIVITY JUST NEAR THE CANADIAN BORDER EARLY
SUNDAY MORNING. LOWS IN THE 50S.
UPPER LEVEL RIDGE BUILDING OVER WESTERN WASHINGTON SUNDAY MOVING
EAST MONDAY. ONSHORE FLOW IN THE LOWER LEVELS SUNDAY THROUGH
TUESDAY FOR AN AREAS MORNING LOW CLOUDS AND AFTERNOON SUNSHINE
FORECAST. HIGH TEMPERATURES NEAR OR JUST SLIGHTLY BELOW NORMAL.
DEEP UPPER LEVEL LOW IN THE GULF OF ALASKA MONDAY NIGHT THROUGH
WEDNESDAY. SOUTHWESTERLY FLOW ALOFT OVER THE AREA. WEAK SYSTEM
KICKING OUT OF THE LOW BRUSHING THE AREA TUESDAY NIGHT FOR A
SLIGHT CHANCE OF SHOWERS. INCREASING ONSHORE FLOW BEHIND THE
SYSTEM LOWERING HIGH TEMPERATURES BACK DOWN INTO THE MID 60S TO
MID 70S FOR WEDNESDAY. FELTON
AVIATION
LIGHT WEST SOUTHWESTERLY FLOW ALOFT BECOMING SOUTHERLY TONIGHT
AND REMAINING SOUTHERLY FRIDAY. LIGHT ONSHORE FLOW TODAY WITH
THE LOW LEVEL FLOW GOING FLAT TONIGHT AND FRIDAY.
LIFR CEILINGS WEST OF PUGET SOUND THIS MORNING WITH LOCAL
VISIBILITIES LESS THAN A MILE IN TERRAIN ABOVE 300 FEET.
CEILINGS LIFTING THEN DISSIPATING 17Z OVER THE LOWLANDS AND BY
20Z ALONG THE COAST AS THE MARINE LAYER RETREATS BACK OFF THE
COASTLINE. PUGET SOUND EASTWARD JUST SOME PATCHY VALLEY FOG
UNTIL 16Z.
INCREASING MIDDLE AND HIGH LEVEL CLOUDS TONIGHT WITH INCREASING
SOUTHERLY FLOW ALOFT. STRATUS STAYING WEST OF PUGET SOUND AGAIN
FRIDAY MORNING.
KSEA...MOSTLY CLEAR SKIES TODAY WITH NORTHERLY WINDS 4 TO 8
KNOTS INCREASING TO 8 TO 12 KNOTS BETWEEN 23Z AND 04Z. FELTON
MARINE
BROAD HIGH PRESSURE OVER THE WATERS WILL WEAKEN FRIDAY. A WEAK
SURFACE LOW WILL MOVE INTO THE COASTAL WATERS SATURDAY WITH THE
ASSOCIATED SYSTEM MOVING THROUGH THE INLAND WATERS SATURDAY
MORNING INTO EARLY AFTERNOON. THE LOW WILL DISSIPATE SATURDAY
NIGHT. HIGH PRESSURE WILL REBUILD SUNDAY AND REMAIN OVER THE
AREA THROUGH MONDAY.
WINDS PICKING UP WITH AND BEHIND THE SYSTEM SATURDAY BUT AT THIS
POINT LOOKS LIKE THE WINDS WILL PEAK AROUND 20 KNOTS OVER THE
WATERS. DIURNAL WESTERLY PUSHES THROUGH THE STRAIT OF JUAN DE
FUCA ALSO PRODUCING UP TO 20 KNOT WINDS IN THE EVENING HOURS.
SEAS REMAINING MOSTLY IN THE 3 TO 5 FOOT RANGE FOR THE NEXT FEW
DAYS. FELTON
FIRE WEATHER
ABOVE NORMAL TEMPERATURES THE NEXT COUPLE OF DAYS BUT MORNING
LOWS DROPPING INTO THE 50S WITH GOOD RELATIVE HUMIDITY
RECOVERIES KEEPING FIRE WEATHER CONCERNS AT A MINIMUM.
UPPER LEVEL MOVING OFF THE COAST SATURDAY AND INTO SOUTHERN
BRITISH COLUMBIA SATURDAY NIGHT/EARLY SUNDAY MORNING. FIRE
WEATHER CONCERNS ELEVATED SATURDAY AS THIS FEATURE WILL BRING
CONVECTION TO THE AREA LATE FRIDAY NIGHT THROUGH SATURDAY
MORNING. THE HIGHEST CHANCE FOR CONVECTION IS OVER THE OLYMPICS
AND CASCADES BUT EVEN THE LOWLANDS WILL HAVE A THREAT OF
THUNDERSTORMS. RAINFALL AMOUNTS HAVE INCREASED FOR THIS SYSTEM,
AND LOCALIZED WETTING RAINS ARE POSSIBLE WITH ANY STORMS THAT
DEVELOP ALONGSIDE GUSTY AND ERRATIC OUTFLOW WINDS AND ABUNDANT
LIGHTNING. COOL DAY SATURDAY WITH THE CONVECTIVE ACTIVITY.
INCREASING ONSHORE FLOW BEHIND THE LOW WILL KEEP TEMPERATURES
COOL AND THE AIR MASS MOIST SUNDAY INTO MONDAY. ANY LIGHTNING
STRIKE MAY NOT HAVE LONG TO SMOLDER WITH MINIMUM RELATIVE
HUMIDITY VALUES BOTTOMING OUT IN THE 60-70% RANGE SATURDAY.
LOW LEVEL ONSHORE FLOW CONTINUING MONDAY INTO TUESDAY BRINGING
HIGH RELATIVE HUMIDITY RECOVERIES IN THE OVERNIGHT HOURS
REDUCING THE FIRE WEATHER CONCERNS. FELTON
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...NONE.
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