189
FXUS66 KSEW 201018
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
318 AM PDT TUE OCT 20 2026
SYNOPSIS
UPPER LEVEL LOW REMAINING WELL SOUTH THROUGH WEDNESDAY WITH
ZONAL FLOW ALOFT OVER THE AREA. WEAK UPPER LEVEL TROUGH MOVING
THROUGH THURSDAY INTO THURSDAY NIGHT. WESTERN WASHINGTON IN
BETWEEN SYSTEMS FRIDAY. LOTS OF UNCERTAINTY REMAINS IN THE WEEKEND
FORECAST WITH THE BEST CHANCES FOR A FRONT MOVING THROUGH LATER
SATURDAY INTO SUNDAY MORNING. UPPER LEVEL RIDGE BUILDING
MONDAY.
SHORT TERM /TODAY THROUGH THURSDAY/
SATELLITE IMAGERY SHOWS HIGH CLOUDS OVER THE SOUTHERN PORTION OF
THE AREA WITH LOW CLOUDS AND FOG NEAR THE WATER IN WHATCOM,
SKAGIT AND SNOHOMISH COUNTIES. CLEAR SKIES ELSEWHERE.
TEMPERATURES AT 3 AM/10Z WERE IN THE MID 30S TO UPPER 40S.
NOT MUCH GOING ON TODAY WEATHERWISE. LARGE UPPER LEVEL LOW WELL
SOUTH AND LIGHT FLOW ALOFT OVER THE AREA. LIGHT NORTHERLY FLOW
IN THE LOWER LEVELS NOT STRONG ENOUGH TO PREVENT FOG AND LOW
CLOUDS FROM FORMING ESPECIALLY NEAR THE PUGET SOUND. THIS
SCENARIO IS ALSO FAVORABLE FOR THE DEVELOPMENT OF LAKE
WASHINGTON STRATUS JUST AFTER SUNRISE. ALL OF THE LOW CLOUDS AND
FOG WILL BE GONE BY LATE MORNING. HIGHS IN THE UPPER 50S TO MID
60S.
LITTLE CHANGE IN THE UPPER PATTERN TONIGHT. IN THE LOWER LEVELS
FLOW GOING LIGHT OFFSHORE BUT NOT STRONG ENOUGH TO PREVENT
PATCHY FOG FORMING AGAIN IN THE EARLY MORNING HOURS. LOWS IN THE
LOWER 30S TO LOWER 40S.
SHALLOW LOW CLOUDS AND FOG DISSIPATING IN THE MORNING HOURS
WEDNESDAY. THE LIGHT OFFSHORE FLOW WILL ADD A COUPLE OF DEGREES
TO THE HIGHS, MOSTLY IN THE 60S. WHILE NOT EXPECTING ANY RECORDS
WE ARE GETTING TO THE TIME OF YEAR WHERE RECORD HIGHS CAN BE IN
THE MID TO UPPER 60S.
WEAK UPPER LEVEL TROUGH DEVELOPING OFFSHORE WEDNESDAY NIGHT WITH
THE TROUGH AXIS NEAR THE COAST BY 00Z FRIDAY. NOTHING IN THE WAY
OF PRECIPITATION WITH THE APPROACH OF THE TROUGH, JUST AN
INCREASE IN CLOUD COVER. LOWS IN THE MID 30S TO MID 40S. HIGHS
MUCH COOLER, IN THE MID TO UPPER 50S.
LONG TERM /THURSDAY NIGHT THROUGH MONDAY/
EXTENDED MODELS IN GOOD AGREEMENT EARLY ON WITH THE UPPER LEVEL
TROUGH MOVING THROUGH THURSDAY NIGHT FOR A CHANCE OF SHOWERS
ESPECIALLY IN THE MOUNTAINS. ZONAL FLOW ALOFT FRIDAY WITH
NOTHING EMBEDDED IN THE FLOW.
ONCE AGAIN CONFIDENCE IS LOW IN THE WEEKEND FORECAST WITH A WIDE
VARIETY OF SOLUTIONS IN THE MODEL ENSEMBLES. THE SOLUTION WITH
THE MOST MEMBERS IS A FRONT MOVING THROUGH THE AREA SATURDAY
NIGHT/SUNDAY MORNING. THERE IS ANOTHER GROUP OF SOLUTIONS THAT
HAS THE FRONT BRUSHING THE AREA DURING THE SAME TIME FRAME.
THERE IS EVEN A FEW SOLUTIONS WITH AN UPPER LEVEL RIDGE BUILDING
OVER WESTERN WASHINGTON. THERE IS GOOD AGREEMENT THAT SAID UPPER
LEVEL RIDGE WILL BUILD/BE OVER THE AREA MONDAY. AT THIS POINT
WILL GO WITH THE CHANCE OF RAIN SATURDAY, RAIN LIKELY/CHANCE OF
RAIN SATURDAY NIGHT INTO SUNDAY MORNING SCENARIO WITH A DRYING
TREND MONDAY. HIGHS IN THE MID AND UPPER 50S. LOWS IN THE MID
30S TO LOWER 40S. IF WE GET THE RIDGING SUNDAY NIGHT THERE IS A
GOOD CHANCE MONDAY WILL BE THE COOLEST MORNING OF THE SEASON.
FELTON
AVIATION
SOUTHERLY FLOW ALOFT TURNING MORE SOUTHWESTERLY BY LATE THIS
AFTERNOON/EARLY THIS EVENING AND INTO WEDNESDAY. AT THE SURFACE,
MANY TERMINALS REPORTING LIGHT AND VARIABLE WINDS WHILE SEA, PWT AND
PAE FAVORING NORTH TO NORTHEASTERLY WINDS WITH SPEEDS 4-8 KTS. AS
WINDS PICK UP IN SPEED SLIGHTLY LATE THIS MORNING TO 5-10 KTS, THE
NORTH TO NORTHEASTERLY DIRECTION WILL CONTINUE TO BE FAVORED IN
GENERAL.
WIDESPREAD VFR CONDITIONS IN PLACE FOR MUCH OF W WA THIS EARLY
MORNING, HOWEVER LOWER CIGS ALREADY PRESENT AT BLI AND PAE BRINGING
ISOLATED IFR/LIFR CONDITIONS THERE. AS OF THIS WRITING, STARTING TO
SEE SOME FOG DEVELOPMENT AT OLM AS WELL AND WOULD EXPECT AT LEAST
IFR CONDITIONS TO EMERGE THERE BY 14Z THIS MORNING. UNIVERSAL VFR
CONDITIONS EXPECTED TO RESUME BY LATE MORNING AND REMAIN THAT WAY
FOR THE REST OF THE TAF PERIOD. MODEL GUIDANCE IS HINTING AT
ISOLATED LOW CIGS/FOG BY EARLY WEDNESDAY MORNING, BUT CONFIDENCE IS
LOW REGARDING WHICH TERMINAL OR TERMINALS MAY SEE IT.
KSEA...VFR CONDITIONS EXPECTED THROUGH THE PERIOD, ALTHOUGH LATEST
GUIDANCE SUGGESTS PROSPECTS OF LOW CIGS/FOG NEAR 12Z WEDNESDAY. AS
STATED ABOVE, CONFIDENCE IS LOW AT THIS TIME AND WILL WAIT TO SEE IF
THIS SOLUTION PERSISTS IN FUTURE HI-RES RUNS. NE WINDS 4-8 KTS THIS
MORNING SHIFTING MORE NW BY AFTERNOON. SPEEDS WILL REMAIN WITHIN
THAT 4-8 KT RANGE FOR THE PERIOD, ALTHOUGH MAY LEAN TOWARD THE
HIGHER END OF THAT RANGE IN THE AFTERNOON AND EARLY EVENING.
18
MARINE
NORTHERLY FLOW WILL PREVAIL OVER THE WATERS WITH LOW PRESSURE
SPINNING OFF NORTHERN CA. WEAK HIGH PRESSURE WILL RESULT IN
GENERALLY LIGHT WINDS THROUGH MID WEEK. ONSHORE FLOW WILL INCREASE
ON THURSDAY/THURSDAY NIGHT AS A COLD FRONT MOVES INLAND.
SEAS GENERALLY 5 TO 7 FT TODAY BEFORE EASING SLIGHTLY TO 4 TO 6 FT
WEDNESDAY. WAVE HEIGHTS RISE THURSDAY NIGHT INTO FRIDAY WITH SWELLS
REACHING 10-15 FEET. WINDS TURN OFFSHORE THIS WEEKEND AS DEEPER LOW
PRESSURE SPINS OVER THE OFFSHORE WATERS.
33/18
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...NONE.
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