808
FXUS66 KSEW 212152
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
252 PM PDT FRI AUG 21 2026
SYNOPSIS
UPPER LEVEL LOW APPROACHING FROM THE SOUTHWEST
FRIDAY WILL MOVE INTO THE COASTAL WATERS SATURDAY AND INTO
SOUTHERN BRITISH COLUMBIA EARLY SUNDAY MORNING. THIS SYSTEM WILL
BRING COOLER WEATHER WITH A CHANCE OF SHOWERS AND THUNDERSTORMS.
UPPER LEVEL RIDGE REBUILDING SUNDAY WILL MOVE EAST MONDAY FOR
DRY AND MILD WEATHER. UPPER LOW SHIFTING INLAND ON WEDNESDAY
WITH SHOWERS RETURNING.
SHORT TERM /TONIGHT THROUGH SUNDAY NIGHT/
HIGH PRESSURE OVER
THE REGION IS BRINGING ONE MORE WARM AND DRY DAY TO WESTERN
WASHINGTON TODAY. HIGHS IN THE INTERIOR ARE IN THE 80S WITH
POCKETS OF MODERATE HEATRISK (MAINLY EAST OF I-5). SATELLITE
DOES SHOW SOME WILDFIRE SMOKE OVER WESTERN WASHINGTON DUE TO
LIGHT EAST WINDS OVER THE CREST. SENSORS ARE SHOWING DEGRADED
AIR QUALITY IN PORTIONS OF WHATCOM COUNTY AND KING COUNTY (DUE
TO THE THREE QUEENS FIRE). THE AIR QUALITY SHOULD IMPROVE ON
SATURDAY AS THE WIND FLOW CHANGES DIRECTIONS.
OUR NEXT SYSTEM WILL MOVE IN LATE TONIGHT AND INTO SATURDAY AND
SUNDAY. THIS SYSTEM WILL BRING COOLER WEATHER ALONG WITH
INCREASING CHANCES OF THUNDERSTORMS. THE HIGHEST CHANCES OF
THUNDERSTORMS WILL BE IN THE MOUNTAINS, ESPECIALLY ACROSS THE
NORTHERN CASCADES. THE HIGHEST CHANCES OF WETTING RAINS WILL BE
NEAR THE CANADIAN BORDER. WITH THE COLDER AIR MASS IN PLACE,
SATURDAY'S HIGHS WILL BE COOLER AND IN THE 60S TO LOWER 70S
ACROSS MOST AREAS. SHOWERS WILL LINGER ON SUNDAY (MAINLY NORTH
PART) AS THE LOW TRACKS N/NE INTO B.C. 33
LONG TERM /MONDAY THROUGH FRIDAY/
HIGH PRESSURE RETURNS EARLY
NEXT WEEK FOR MORE DRY AND MILD WEATHER. THE FLOW REMAINS
ONSHORE WITH TEMPERATURES CLOSE TO AVERAGE. THE RIDGE WILL
STALL AN UPPER LOW OFFSHORE THAT WILL EVENTUALLY SHIFT INLAND BY
MIDWEEK FOR ANOTHER ROUND OF SHOWERS. THE LOW AND COOLER AIR
MASS WILL RESULT IN BELOW AVERAGE TEMPERATURES IN THE 60S AND
LOWER/MID 70S. WE'RE UNDER WEAK TROUGHING THROUGH THE END OF THE
WEEK WITH ISOLATED MOUNTAIN SHOWERS. 33
AVIATION
SOUTHERLY FLOW ALOFT WILL INCREASE TONIGHT INTO SATURDAY
AS AN UPPER LOW OFFSHORE APPROACHES WESTERN WASHINGTON. VFR CIGS FOR
THE MAJORITY OF TERMINALS THIS AFTERNOON WITH INCREASING MID AND
HIGH CLOUDS. MVFR/IFR STRATUS CONTINUES ALONG PORTIONS OF THE COAST.
STRATUS WILL MOVE INLAND INTO PUGET SOUND INTO SATURDAY MORNING,
RESULTING IN MORE WIDESPREAD MVFR/IFR CIGS. LIFR STRATUS WILL EXIST
ALONG PORTIONS OF THE COAST TONIGHT INTO SATURDAY AS WELL. SHOWERS
AND A FEW THUNDERSTORMS ARE EXPECTED TO DEVELOP LATE TONIGHT INTO
SATURDAY. PROBABILITIES FOR THUNDERSTORMS RANGE TO 10 TO 20 PERCENT
FOR ALL TERMINALS, WITH THE HIGHER PROBABILITIES FROM KPAE
NORTHWARDS. CIGS WILL IMPROVE TO VFR FOR INTERIOR LOCATIONS BY THE
AFTERNOON. W/NW WINDS THIS AFTERNOON WILL TRANSITION MORE SW TONIGHT
AND INCREASE INTO SATURDAY.
KSEA...VFR WITH MID AND HIGH CLOUDS INTO TONIGHT. STRATUS WILL
SPREAD INLAND EARLY SATURDAY, REACHING THE TERMINAL AROUND 12Z.
PREDOMINANTLY LOW-END MVFR CIGS ARE EXPECTED. THERE IS A 20%
PROBABILITY OF IFR CIGS BETWEEN 13 TO 17Z AS WELL. CIGS WILL SLOWLY
IMPROVE TO VFR INTO THE AFTERNOON, BETWEEN 19 TO 21Z. SHOWERS AND A
FEW THUNDERSTORMS ARE EXPECTED TO DEVELOP EARLY SATURDAY MORNING.
CONFIDENCE REMAINS LOWER IN THE EXACT LOCATION FOR PRECIPITATION,
BUT THERE IS A 10 TO 15% PROBABILITY FOR THUNDERSTORMS AROUND THE
TERMINAL SATURDAY, PEAKING BETWEEN 12 TO 20Z. W/NW SURFACE WINDS
RANGING 5 TO 8 KTS WILL TRANSITION SW AFTER 00-01Z. JD
MARINE
ONSHORE FLOW WILL INCREASE THIS EVENING RESULTING SMALL
CRAFT WESTERLY WINDS THROUGH THE STRAIT OF JUAN DE FUCA TONIGHT. A
WEAK SURFACE LOW THEN MOVES INTO THE COASTAL WATERS SATURDAY BEFORE
THE LOW DISSIPATES SATURDAY NIGHT. SHOWERS WILL DEVELOP LATE TONIGHT
INTO SATURDAY ASSOCIATED WITH THE SYSTEM. THERE IS A ALSO A SLIGHT
CHANCE (10-20%) FOR THUNDERSTORMS OVER BOTH THE COASTAL AND INTERIOR
WATERS ON SATURDAY. SOUTH TO SOUTHWEST WINDS WILL ALSO INCREASE ON
SATURDAY, WITH GUSTS RANGING 15 TO 20 KTS FOR PORTIONS OF THE
INTERIOR WATERS AND INNER COASTAL WATERS. HIGH PRESSURE REBUILDS
SUNDAY AND REMAINS OVER THE AREA INTO TUESDAY. A COLD FRONT MOVES
INTO THE WATERS BY MIDWEEK.
SEAS WILL MOSTLY BE IN THE 3 TO 5 FOOT RANGE INTO EARLY NEXT
WEEK. JD
FIRE WEATHER
DRY AND WARM CONDITIONS CONTINUING TODAY.
CRITICAL RHS HAVE BEEN OBSERVED FOR LOCATIONS ABOVE 2500 FT SO
FAR THIS AFTERNOON. INCREASING CLOUD COVERAGE AND CONTINUED LOW-
LEVEL ONSHORE FLOW THIS EVENING. THEN, AN UPPER-LOW OFFSHORE
WILL TRACK INTO THE REGION LATE TONIGHT INTO EARLY SATURDAY WITH
THE POTENTIAL FOR SCATTERED SHOWERS AND THUNDERSTORMS. AS A
RESULT, A RED FLAG WARNING HAS BEEN ISSUED FOR THE CASCADE AND
OLYMPIC MOUNTAINS LATE TONIGHT INTO SATURDAY EVENING. THE NORTH
CASCADES ARE CURRENTLY THE MOST FAVORABLE FOR THUNDERSTORMS AT
THIS TIME WITH A 30-40% CHANCE. LIGHTNING MAY LEAD TO NEW FIRE
STARTS, AS WELL AS RESULT IN GUSTY AND ERRATIC WINDS.
LOW LEVEL ONSHORE FLOW INCREASES SATURDAY NIGHT INTO SUNDAY WITH
VARYING DEGREES OF ONSHORE FLOW THROUGH THE MIDDLE OF NEXT WEEK.
GOOD RELATIVE HUMIDITY RECOVERIES EACH NIGHT WILL KEEP FIRE WEATHER
CONCERNS AT A MINIMUM. CHANCE OF SHOWERS AND POSSIBLE THUNDERSTORMS
NEXT WEDNESDAY WITH AN UPPER LEVEL TROUGH MOVING INTO THE AREA.
41
SEW WATCHES/WARNINGS/ADVISORIES
WA...RED FLAG WARNING FROM 5 AM TO 8 PM PDT SATURDAY FOR WEST
SLOPES OF THE NORTH CASCADES GENERALLY ABOVE 1500 FEET.
RED FLAG WARNING FROM 1 AM TO 5 PM PDT SATURDAY FOR EAST
PORTION OF THE OLYMPIC MOUNTAINS-WEST PORTION OF THE
OLYMPIC MOUNTAINS-WEST SLOPES OF THE CENTRAL CASCADES
GENERALLY ABOVE 1500 FEET.
PZ...SMALL CRAFT ADVISORY FROM 6 PM THIS EVENING TO 6 AM PDT
SATURDAY FOR CENTRAL U.S. WATERS STRAIT OF JUAN DE FUCA-
EAST ENTRANCE U.S. WATERS STRAIT OF JUAN DE FUCA.
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