793
FXUS66 KSEW 171035
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
335 AM PDT SAT OCT 17 2026
SYNOPSIS
WEAKENING FRONTAL SYSTEM MOVING THROUGH THE AREA EARLY THIS
MORNING. POST FRONTAL CONVERGENCE ZONE LATER THIS MORNING
DISSIPATING THIS 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/
SATELLITE IMAGERY AND DOPPLER RADAR SHOWS WEAKENING FRONT HAS
MOVED INTO THE NORTHWEST INTERIOR IN THE LAST HOUR. RAIN ALONG
THE COAST IS COMING TO AN END WHILE OVER THE INTERIOR AS OF 3 AM
THE RAIN IS CONFINED TO THE SAN JUANS AND SKAGIT COUNTY
NORTHWARD. TEMPERATURES WITH THE CLOUD COVER WERE IN THE 50S.
FRONT WILL CONTINUE TO WEAKEN AND MOVE INTO THE CASCADES IN THE
NEXT THREE HOURS. MOST OF THE RAINFALL WITH THE FRONT THIS
MORNING WILL BE FROM SNOHOMISH COUNTY NORTHWARD WITH JUST A
CHANCE FOR SHOWERS KING COUNTY SOUTHWARD. POST FRONTAL
CONVERGENCE ZONE FORMING QUICKLY BETWEEN 12Z AND 15Z. BOTH THE
KUIL-KBLI AND KOLM-KBLI GRADIENTS HAVE INCREASED FROM NEAR 1 MB
TO NEAR 2.5 MB IN THE LAST TWO HOURS. CONVERGENCE ZONE SETTING
UP OVER SNOHOMISH AND NORTHERN KING COUNTY WILL WEAKEN AND MOVE
INTO THE CASCADES LATE MORNING/MIDDAY. 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
SOUTHWESTERLY FLOW ALOFT TURNING WESTERLY BY THE EVENING AS A
FRONTAL SYSTEM TRACKS THROUGH THE AREA. MOSTLY VFR OBSERVED SO FAR
THIS MORNING ASIDE FROM KHQM & KBLI (MVFR/IFR) WHERE THE FRONT IS
SPREADING RAINFALL. BRIEF MVFR CIGS WILL SPREAD ACROSS THE INTERIOR
AS THE MORNING PROGRESS ALONG WITH RAIN AND SHOWERS. A RETURN TO
WIDESPREAD VFR IS EXPECTED BY THE AFTERNOON AND LEAD WELL INTO THE
EVENING. SOUTHERLY WIND GUSTS UP TO 20 KT THIS MORNING, DECREASES
WELL INTO THE DAY.
KSEA... VFR CIGS IN PLACE SO FAR THIS MORNING. MVFR CONDITIONS
EXPECTED TO PICK UP BY 12Z WITH ACCOMPANYING PRECIP THANKS TO
APPROACHING WEAK FRONTAL SYSTEM. THE BULK OF THE RAIN WILL BE DONE
BY 17Z, WITH ISOLATED SHOWERS POSSIBLE IN THE AFTERNOON. VFR
CONDITIONS EXPECTED TO RETURN THEREAFTER WITH FAIR SKIES ON TAP BY
THE MID-AFTERNOON. SOUTHERLY WIND GUSTS UP TO 20 KT POSSIBLE THIS
MORNING BEFORE WINDS DECREASE AND TURN MORE NORTHERLY IN THE
AFTERNOON.
41
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 FROM 6 AM THIS MORNING TO 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 FROM 6 AM THIS MORNING TO 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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