750
FXUS66 KSEW 171634
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
934 AM PDT SAT OCT 17 2026
SYNOPSIS
A POST FRONTAL CONVERGENCE ZONE CONTINUES THIS
MORNING, DISSIPATING IN THE AFTERNOON. UPPER LEVEL TROUGH
OFFSHORE DIGGING SOUTH SUNDAY AND MONDAY WITH THE NEXT SYSTEM
MOVING BY TO THE WEST. TEMPORARY UPPER LEVEL RIDGE TUESDAY
MOVING EAST WEDNESDAY. ANOTHER SPLITTING SYSTEM ARRIVING
THURSDAY. COOL UPPER LEVEL TROUGH OVER WESTERN WASHINGTON
FRIDAY.
SHORT TERM /TODAY THROUGH MONDAY/
A CONVERGENCE ZONE
CONTINUES THIS MORNING ACROSS KING COUNTY INTO THE CENTRAL
CASCADES. PRECIPITATION WILL SLOWLY DISSIPATE IN THIS AREA INTO
THE EARLY AFTERNOON. OUTSIDE OF THE CONVERGENCE ZONE NOT MUCH
IN THE WAY OF COOL AIR BEHIND THE FRONT LEADING TO MINIMAL POST
FRONTAL SHOWER ACTIVITY. SKIES CLEARING THIS AFTERNOON WITH
PARTLY TO MOSTLY SUNNY SKIES ACROSS THE AREA. WITH THE SUNSHINE
HIGHS NEAR OR SLIGHTLY ABOVE NORMAL, IN THE UPPER 50S TO MID
60S.
NOT MUCH GOING ON TONIGHT. ZONAL FLOW ALOFT WITH SURFACE HIGH
PRESSURE BUILDING INTO THE AREA. LIGHT GRADIENTS OVERNIGHT
BRINGS UP THE POTENTIAL FOR SOME FOG FORMATION EARLY SUNDAY
MORNING ESPECIALLY IN THE FOG PRONE LOCATIONS LIKE THE SOUTHWEST
INTERIOR. LOWS IN THE MID 30S TO MID 40S.
SURFACE HIGH PRESSURE REMAINING OVER WESTERN WASHINGTON SUNDAY.
FLOW ALOFT BECOMING SOUTHWESTERLY WITH AN UPPER LEVEL TROUGH
KICKING OUT OF THE GULF OF ALASKA DIGGING SOUTH WELL OFFSHORE.
THIS WILL SPREAD SOME HIGH CLOUDS OVER THE AREA DURING THE DAY.
HIGHS A LITTLE COOLER WITH THE COOL MORNING TO START THINGS
OFF, IN THE MID 50S TO LOWER 60S.
UPPER LEVEL TROUGH CONTINUING TO DIG SOUTH SUNDAY NIGHT INTO
MONDAY WITH THE ASSOCIATED FRONTAL SYSTEM MOVING BY TO THE WEST
MONDAY. RAIN CHANCES CONFINED TO THE COASTAL WATERS BUT WITH THE
SYSTEM IN THE VICINITY PLENTY OF MIDDLE AND HIGH LEVEL CLOUD
COVER BY MONDAY. LOWS IN THE MID 30S TO MID 40S. HIGHS MONDAY
AGAIN IN THE MID 50S TO LOWER 60S. FELTON
LONG TERM /MONDAY NIGHT THROUGH FRIDAY/
MODELS IN GOOD
AGREEMENT WITH THE UPPER LEVEL TROUGH DROPPING DOWN THE
CALIFORNIA COAST THROUGH TUESDAY LEAVING WESTERN WASHINGTON IN A
LULL. SURFACE GRADIENTS GOING NORTHERLY FOR ANOTHER DRY DAY
TUESDAY WITH HIGHS NEAR NORMAL, MID 50S TO LOWER 60S. COOL
MORNINGS BOTH TUESDAY AND WEDNESDAY WITH THE COLDEST LOCATIONS
NEAR FREEZING. ANOTHER ROUND OF FROST ADVISORIES MAY BE NEEDED.
UPPER LEVEL TROUGH APPROACHING THE COAST WEDNESDAY. FRONTAL
SYSTEM ASSOCIATED WITH THE TROUGH STILL WELL OFFSHORE WEDNESDAY
AFTERNOON. MOSTLY SUNNY SKIES WITH HIGHS A TOUCH WARMER, UPPER
50S TO MID 60S.
FRONT SLOWING DOWN AND SPLITTING WEDNESDAY NIGHT WITH WHAT IS
LEFT OF THE SYSTEM MOVING INLAND THURSDAY FOR A CHANCE OF
SHOWERS. LOWS IN THE MID 30S TO MID 40S. HIGHS IN THE MID TO
UPPER 50S.
POSSIBLE POST FRONTAL CONVERGENCE ZONE THURSDAY NIGHT. WEAK
UPPER LEVEL TROUGH MOVING OVER THE AREA HANGING AROUND THROUGH
FRIDAY. CHANCE OF SHOWERS THURSDAY NIGHT BECOMING CONFINED TO
THE CASCADES FRIDAY. LITTLE CHANGE IN TEMPERATURES FROM
THURSDAY'S HIGHS AND LOWS.
QUICK NOTE ON THE 77 DEGREE DAY IN SEATTLE FRIDAY. THIS WAS THE
SECOND WARMEST DAY ON RECORD FOR THIS LATE IN THE YEAR. THE ONLY
DAY WARMER WAS THE RECORD SETTING 88 DEGREE DAY BACK IN 2022.
THE WARMEST DAYS ON RECORD FROM HERE UNTIL MARCH ARE 74 DEGREE
DAYS ON OCTOBER 17, 1989, NOVEMBER 3 2010 AND NOVEMBER 4, 1949.
77 DEGREES IS THE NORMAL HIGH IN SEATTLE FROM AUGUST 19 THROUGH
25. THE NORMAL HIGH FOR SEATTLE YESTERDAY IS 60 DEGREES. FELTON
AVIATION
WESTERLY FLOW ALOFT WILL CONTINUE INTO TONIGHT AS A
FRONTAL SYSTEM SHIFTS EAST OF THE AREA. THE LOW LEVEL FLOW IS
ONSHORE AND WILL GRADUALLY WEAKEN THIS AFTERNOON INTO TONIGHT.
MVFR CEILINGS AND A FEW POCKETS OF IFR IN RAIN REMAIN AROUND
CENTRAL PUGET SOUND THIS MORNING AS A CONVERGENCE ZONE GRADUALLY
SHIFTS SOUTHWARD INTO KING COUNTY. CEILINGS WILL IMPROVE AROUND
PUGET SOUND TOWARD MID- AFTERNOON AS THE CONVERGENCE ZONE
DISSIPATES WITH VFR EXPECTED FOR THE REMAINDER OF THE AREA THIS
AFTERNOON. LIGHT SURFACE WINDS AND LOW LEVEL MOISTURE WILL LEAD
TO THE FORMATION OF IFR/LIFR FOG AND LOW CLOUDS ON SUNDAY
MORNING...ESPECIALLY ACROSS THE SOUTHWEST INTERIOR AND SOUTH
PORTIONS OF PUGET SOUND.
KSEA...THE CONVERGENCE ZONE IS SHIFTING SOUTHWARD INTO NORTHERN
PORTIONS OF KING COUNTY AS OF 16Z WITH A N/NE WIND SHIFT ON TRACK TO
REACH THE TERMINAL AROUND 18Z-19Z. CEILINGS ARE EXPECTED TO LIFT TO
VFR TOWARD 20Z OR SO AS THE CONVERGENCE ZONE BEGINS TO DISSIPATE.
CONFIDENCE IS FAIRLY HIGH THAT SOME LIFR FOG AND LOW CLOUDS WILL BE
AROUND THE TERMINAL ON SUNDAY MORNING AND WILL INCLUDE THAT IN
UPCOMING TAF. SURFACE WINDS SHIFTING TO E/NE AROUND 18Z THEN
BECOMING N/NE 5 TO 8 KNOTS THIS AFTERNOON INTO TONIGHT.
27
MARINE
A FRONTAL SYSTEM IS MOVING THROUGH THE AREA THIS
MORNING. SEAS WILL BE BETWEEN 8-10 FEET WITH THE HIGHEST WAVES
OVER THE OFFSHORE WATERS. AS A RESULT, SCAS REMAIN OVER THE
OUTER COASTAL WATERS (FOR SEAS) AND CENTRAL/EASTERN STRAIT (FOR
WINDS) UNTIL TONIGHT. HIGH PRESSURE BUILDING OVER THE WATERS
SATURDAY AFTERNOON WILL REMAIN THROUGH SUNDAY. ANOTHER SYSTEM
WILL MOVE BY WEST OF THE COASTAL WATERS MONDAY. HIGH PRESSURE
WILL REBUILD OVER THE AREA TUESDAY WITH SEAS SUBSIDING BACK DOWN
TO 4 TO 6 FEET AROUND THIS TIME.
41
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...SMALL CRAFT ADVISORY UNTIL 6 PM PDT THIS EVENING FOR CENTRAL
U.S. WATERS STRAIT OF JUAN DE FUCA-EAST ENTRANCE U.S.
WATERS STRAIT OF JUAN DE FUCA.
SMALL CRAFT ADVISORY UNTIL 8 PM PDT THIS EVENING FOR COASTAL
WATERS FROM CAPE FLATTERY TO JAMES ISLAND 10 TO 60 NM-
COASTAL WATERS FROM JAMES ISLAND TO POINT GRENVILLE 10 TO
60 NM-COASTAL WATERS FROM POINT GRENVILLE TO CAPE
SHOALWATER 10 TO 60 NM.
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