253
FXUS66 KSEW 201528
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
828 AM PDT SUN SEP 20 2026
SYNOPSIS
HIGH PRESSURE ALOFT WITH LIGHT FLOW IN THE LOWER
LEVELS THROUGH TONIGHT. RIDGE WEAKENING MONDAY AS A WEAK SYSTEM
MOVES BY TO THE NORTH. ANOTHER WEAK SYSTEM WILL BRUSH THE
NORTHERN PORTIONS WEDNESDAY. UPPER LEVEL TROUGH DEVELOPING
OFFSHORE WEDNESDAY NIGHT AND THURSDAY WITH A MORE ORGANIZED
SYSTEM ARRIVING THURSDAY NIGHT OR FRIDAY.
SHORT TERM /TODAY THROUGH TUESDAY/
SHALLOW STRATUS AND AREAS
OF FOG CONTINUE THIS MORNING, ESPECIALLY ALONG THE CASCADE
FOOTHILLS, SOUTHERN PUGET SOUND, AND OLYMPIC PENINSULA. SLOW
CLEARING IS EXPECTED INTO EARLY AFTERNOON. HIGHS TODAY IN THE
60S.
LITTLE CHANGE IN THE PATTERN TONIGHT. UPPER LEVEL RIDGE MOVING
EAST MONDAY WITH WEAK LOW LEVEL FLOW CONTINUING THROUGH THE
DAY. LOW LEVEL MOISTURE OVER THE AREA ONCE AGAIN TONIGHT INTO
MONDAY MORNING COMBINED WITH THE LIGHT LOW LEVEL FLOW FOR
ANOTHER ROUND OF LOW CLOUDS AND FOG MONDAY MORNING. WEAK SYSTEM
RIDING BY TO THE NORTH LATER IN THE DAY THROWING SOME MIDDLE AND
HIGH LEVEL CLOUDS OVER THE AREA SO EVEN AFTER THE MARINE LAYER
DISSIPATES IT WILL STILL BE MOSTLY CLOUDY. LOWS TONIGHT IN THE
MID 40S TO LOWER 50S. HIGHS MONDAY ONCE AGAIN IN THE 60S.
WEST SOUTHWESTERLY FLOW ALOFT MONDAY NIGHT INTO TUESDAY WITH 500
MB HEIGHTS DROPPING AS AN UPPER LEVEL TROUGH DEVELOPS OFFSHORE.
WEAK SYSTEM SPINNING OUT OF THE TROUGH APPROACHING THE COAST
LATE TUESDAY. A LITTLE MORE FLOW IN THE LOWER LEVELS REDUCING
THE MORNING FOG COVERAGE BUT PLENTY OF LOW LEVEL MOISTURE AROUND
FOR LOW CLOUD FORMATION. LIKE MONDAY BY THE TIME THE MARINE
LAYER DISSIPATES IN THE AFTERNOON MIDDLE AND HIGH LEVEL CLOUDS
AHEAD OF THE NEXT SYSTEM WILL BE SPREADING OVER THE AREA
MAKING FOR ANOTHER MOSTLY CLOUDY DAY. HIGHS IN THE 60S. LOWS
TUESDAY MORNING IN THE MID 40S TO LOWER 50S. FELTON
LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/
MODELS IN GOOD
AGREEMENT WITH THE WEAKENING SYSTEM REACHING THE COAST WEDNESDAY
MORNING DISSIPATING OVER THE INTERIOR IN THE AFTERNOON. CHANCE
OF SHOWERS ALONG THE NORTH COAST TUESDAY NIGHT AND OVER THE
ENTIRE NORTHERN PORTION OF THE AREA WEDNESDAY.
STRONGER UPPER LEVEL TROUGH DIGGING SOUTH OUT OF THE GULF OF
ALASKA WEDNESDAY NIGHT AND THURSDAY. MODELS HAVING A LITTLE
TROUBLE ON THE TIMING OF A DEVELOPING SYSTEM IN THE BASE OF THE
TROUGH THEN MOVING INTO THE AREA. THE TIMING RANGES FROM
THURSDAY AFTERNOON TO THURSDAY NIGHT/FRIDAY MORNING. WITH THE
TROUGH DIGGING OFFSHORE THERE IS A CHANCE THIS FEATURE COULD
STALL OVER WESTERN WASHINGTON FOR A BIT BEFORE KICKING OUT TO
THE EAST. ENSEMBLES FAVOR THE LATER TIMING WITH CHANCE POPS
THURSDAY NIGHT AND CHANCE/LIKELY POPS FRIDAY. UPPER LEVEL TROUGH
MOVING THROUGH FRIDAY NIGHT KEEPING CHANCE POPS IN THE
FORECAST. WEAK SPLIT FLOW ALOFT OFF THE COAST SATURDAY FOR A
GOOD CHANCE AT A DRY DAY.
HIGHS IN THE 60S WEDNESDAY AND THURSDAY AND LOWER TO MID 60S
FRIDAY AND SATURDAY. LOWS IN THE MID 40S TO LOWER 50S. THERE IS
A CHANCE THAT SEATTLE COULD SEE THE FIRST LOW IN THE 40S SINCE
JUNE 8TH ( 49 DEGREES ) SATURDAY MORNING. FELTON
AVIATION
MOSTLY CLEAR SKIES EARLY THIS MORNING WITH LIGHT
WINDS HAS PROMOTED THE DEVELOPMENT OF FOG IN THE VALLEYS ACROSS
WESTERN WASHINGTON. STRATUS WILL CONTINUE TO SLOWLY BUILD ALONG
THE IMMEDIATE COASTLINE, AS WELL. EXISTING FOG IN THE SOUTHERN
PUGET SOUND AREA SHOULD BEGIN TO LIFT AND START TO BURN OUT FROM
17-20Z. FOLLOWING, SKIES WILL REMAIN MOSTLY CLEAR WITH VFR
CONDITIONS THROUGH THE REMAINDER OF THE DAY TODAY. THE PATTERN
LOOKS TO REPEAT WITH ANOTHER ROUND OF FOG AND LOW STRATUS ONCE
AGAIN EARLY MONDAY MORNING. LIGHT TO CALM WINDS THIS MORNING
WILL REMAIN N/NW 4-6 KT DURING THE DAY TODAY.
KSEA...VFR CONDITIONS CONTINUE THIS MORNING. THERE IS A BANK OF LOW
TO MID LEVEL CLOUDS EAST OF THE TERMINAL, BUT GIVEN THE NORTHERLY
FLOW, THESE CLOUDS WILL CONTINUE TO STREAM OFF TOWARD THE SSW
AND GENERALLY MISS THE TERMINAL. SKC INDICATED IN PREVAILING
LINE OF TAF, WITH INTERMITTENT FEW TO SCT 010 THROUGH 17Z-18Z.
VFR CONDITIONS PREVAIL THROUGH THE REST OF THE DAY. ANOTHER
ROUND OF LOW CLOUDS AND FOG ARE POSSIBLE AGAIN AFTER 12Z MONDAY.
LIGHT N WINDS 4 KT OR LESS WILL INCREASE TO AROUND 5-8 KT
TODAY. WINDS REMAIN LIGHT TONIGHT INTO MONDAY MORNING.
62/21
MARINE
HIGH PRESSURE WILL CONTINUE TO PERSIST OVER THE
OFFSHORE WATERS GOING INTO EARLY NEXT WEEK. A WEAK FRONT WILL
GRAZE THE AREA JUST TO THE NORTH LATE MONDAY INTO TUESDAY, WHICH
WILL ALLOW FOR INCREASED ONSHORE FLOW MONDAY NIGHT.
PROBABILITIES FOR SMALL CRAFT ADVISORY WINDS THROUGH THE STRAIT
OF JUAN DE FUCA INCREASE TO 60-90% MONDAY AFTERNOON INTO EARLY
TUESDAY. ANOTHER PUSH IS EXPECTED TUESDAY EVENING, BUT
PROBABILITIES DECREASE AND ARE MORE CONFINED TO THE CANADIAN
SIDE OF THE STRAIT. ADDITIONAL SYSTEMS MAY MOVE THROUGH THE
WATERS WEDNESDAY AND TOWARDS THE END OF THE WEEK BUT WIDESPREAD
STRONGER WINDS ARE NOT LIKELY AT THIS TIME.
VERY CALM SEAS OF AROUND 2 TO 3 FT WILL INCREASE LATE TONIGHT INTO
MONDAY TO AROUND 7 TO 9 FT AS LONGER PERIOD NORTHWESTERLY SWELL
ARRIVES THE COASTAL WATERS. SEAS LOOK TO REMAIN AROUND 6 TO 8 FT
TUESDAY THROUGH THE MIDDLE OF THE WEEK.
62
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...NONE.
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