334
FXUS66 KSEW 211037
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
337 AM PDT WED OCT 21 2026
SYNOPSIS
UPPER LEVEL TROUGH OFFSHORE TODAY AND TONIGHT WILL MOVE INLAND
THURSDAY WITH NOT MUCH MOISTURE ASSOCIATED WITH THE TROUGH.
TEMPORARY RIDGE OVER THE AREA FRIDAY. LOTS OF UNCERTAINTY IN THE
WEEKEND FORECAST WITH A CHANCE OF A SYSTEM MOVING THROUGH
WESTERN WASHINGTON. TRAILING UPPER LEVEL LOW COULD STILL BE
AROUND MONDAY BEFORE AN UPPER LEVEL RIDGE BUILDS MONDAY NIGHT
AND TUESDAY.
SHORT TERM /TODAY THROUGH FRIDAY/
SATELLITE IMAGERY SHOWS FOG IN THE SNOQUALMIE AND SNOHOMISH
RIVER VALLEYS WITH SOME LOW CLOUDS AND FOG NEAR THE WATER IN
WHATCOM, SKAGIT AND SNOHOMISH COUNTY. MOSTLY CLEAR SKIES OVER
THE REMAINDER OF THE AREA. TEMPERATURES AT 3 AM/10Z WERE IN THE
MID 30S TO MID 40S.
LOW LEVEL OFFSHORE FLOW THIS MORNING WILL NOT BE STRONG ENOUGH
TO PREVENT A LITTLE MORE FOG AND LOW CLOUDS FROM FORMING NEAR
THE PUGET SOUND IN THE NEXT COUPLE OF HOURS. THE LAYER WILL BE
SHALLOW WITH SUNNY SKIES ACROSS THE AREA BY MID MORNING. THE
OFFSHORE FLOW WILL ADD A COUPLE OF DEGREES TO THE HIGHS WITH
MOST PLACES IN THE 60S. NOT EXPECTING ANY RECORDS BUT THIS TIME
OF YEAR HIGHS IN THE UPPER 60S CAN BE RECORDS. THE FORECAST HIGH
OF 65 IN SEATTLE WOULD BE THE 10TH WARMEST OCTOBER 21ST IN 82
YEARS OF RECORDS.
LOW LEVEL FLOW TURNING LIGHT TONIGHT AND REMAINING LIGHT INTO
THURSDAY. UPPER LEVEL TROUGH OFFSHORE REACHING THE COAST LATE
THURSDAY INCREASING THE CLOUD COVER OVER THE AREA THURSDAY
AFTERNOON BUT NOT PRODUCING ANY SHOWER ACTIVITY. LOWS TONIGHT IN
THE MID 30S TO MID 40S. COOLER THURSDAY WITH HIGHS IN THE MID
50S TO LOWER 60S.
UPPER LEVEL TROUGH MOVING THROUGH THURSDAY NIGHT PERHAPS GIVING
THE CASCADES A SHOWER OR TWO. MOSTLY CLOUDY SKIES IN THE EVENING
THINNING OUT A LITTLE OVERNIGHT. LOWS IN THE LOWER 30S TO LOWER
40S.
WEAK TEMPORARY UPPER LEVEL RIDGE MOVING THROUGH FRIDAY FOR
ANOTHER DRY DAY. LIGHT ONSHORE FLOW IN THE LOWER LEVELS WITH
MORNING LOW CLOUDS BECOMING AT LEAST PARTLY SUNNY IN THE
AFTERNOON. HIGHS IN THE MID 50S TO LOWER 60S. FELTON
LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/
UPPER LEVEL RIDGE WEAKENING AND MOVING EAST FRIDAY NIGHT.
MODELS CONTINUING TO HAVE TROUBLE COMING TO A CONSISTENT
SOLUTION FOR THE WEEKEND. THE ENSEMBLES FAVOR A WEAK SYSTEM
MOVING THROUGH LATER SATURDAY INTO SUNDAY MORNING. ENSEMBLE
MEAN POPS ARE SLOWLY GETTING LOWER IN THE LAST THREE RUNS WITH
NOW JUST CHANCE POPS FOR EVERYWHERE BUT THE NORTH COAST. UPPER
LEVEL LOW ASSOCIATED WITH THE FRONT HANGING AROUND LATER SUNDAY
INTO SUNDAY NIGHT KEEPING CHANCE/SLIGHT CHANCE POPS IN THE
FORECAST. THERE IS BETTER CONSENSUS WITH AN UPPER LEVEL RIDGE
BUILDING MONDAY OR MONDAY NIGHT FOR A DRY TUESDAY. HIGHS IN THE
50S THROUGH THE PERIOD. IF THE RIDGE DOES BUILD LATER MONDAY
GOOD CHANCE WE SEE SOME LOWS IN THE 20S TUESDAY MORNING. FELTON
AS WE HEAD INTO THE LAST THIRD OF OCTOBER HERE ARE SOME CURRENT
OCTOBER RAINFALL TOTALS IN THE WEST. YOU DON'T SEE THIS VERY
OFTEN. SEATTLE 0.08 INCHES, LOS ANGELES 0.23 INCHES, SAN DIEGO
1.04 INCHES, PALM SPRINGS 1.17 INCHES, LAS VEGAS 1.19 INCHES,
PHOENIX 0.42 INCHES. FELTON
AVIATION
AN UPPER LEVEL LOW CONTINUES TO SPIN OFF CA WITH DRY AND STABLE
CONDITIONS ACROSS WESTERN WA. THE FLOW ALOFT REMAINS SOUTHWESTERLY.
LIGHT AND VARIABLE WINDS IN PLACE FOR ALL TERMINALS THIS EARLY
MORNING EXCEPT FOR HQM, WHERE EASTERLY WINDS RANGING 5-10 KTS ARE
EXPECTED TO REMAIN IN PLACE INTO AT LEAST LATE MORNING/EARLY
AFTERNOON. WIDESPREAD NORTH TO NORTHWESTERLY WINDS EXPECTED BY NOON
TODAY ALTHOUGH SPEEDS EXPECTED TO GENERALLY REMAIN LESS THAN 5 OR 6
KTS FOR THE REMAINDER OF THE TAF PERIOD. HQM MAY START THE AFTERNOON
RANGING 4-8 KTS BUT WINDS THERE WILL ALSO EASE TO AROUND 5 KTS BY
THIS EVENING.
WIDESPREAD VFR CONDITIONS IN PLACE OVER MUCH OF W WA THIS EARLY
MORNING, HOWEVER STARTING TO SEE HINTS OF LOW STRATUS AND FOG FOR
TERMINALS ALONG THE EASTERN SOUND VERY SIMILAR TO TUESDAY
MORNING...SO EXPECT CONDITIONS TO DEGRADE THERE DOWN INTO IFR/LIFR
BETWEEN 12-15Z AND PERSIST INTO THE 18-20Z TIME FRAME. VFR
CONDITIONS RETURN FOR THE REMAINDER OF THE TAF PERIOD.
KSEA...VFR CONDITIONS AS OF 09Z, BUT A BRIEF PERIOD OF
SHALLOW/PATCHY FOG IS POSSIBLE STARTING BETWEEN 12-15Z FOR LIFR
CONDITIONS BEFORE VFR CONDITIONS RETURN AFTER 18Z. LIGHT AND
VARIABLE WINDS THIS MORNING BEFORE BECOMING MORE NW THIS AFTERNOON
WITH SPEEDS AROUND 5 KT. WINDS WILL SHIFT NORTHERLY THIS EVENING
WHILE SPEEDS REMAIN THE SAME.
18
MARINE
WEAK HIGH PRESSURE WILL LEAD TO GENERALLY LIGHT WINDS OVER THE
WATERS AGAIN TODAY. ONSHORE FLOW WILL INCREASE ON THURSDAY AS A COLD
FRONT MOVES INLAND. SEAS WILL BUILD TO 10-15 FT THURSDAY NIGHT THEN
GRADUALLY SUBSIDE UNDER 10 FT ON FRIDAY. SINCE BOTH WINDS AND WAVES
WILL MEET SCA CRITERIA FOR THE COASTAL WATERS THURSDAY, WENT AHEAD
AND ISSUED THE HEADLINE WITH GOOD LEVEL OF CONFIDENCE AS MODELS
HAVE BEEN ADVERTISING THIS FOR SOME TIME. THE FLOW WILL TURN
OFFSHORE THIS WEEKEND AS A THERMAL TROUGH FORMS ALONG THE COAST. LOW
PRESSURE WILL WEAKEN OVER THE OFFSHORE WATERS EARLY NEXT WEEK. 33/18
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...SMALL CRAFT ADVISORY FROM 2 PM THURSDAY TO 11 AM PDT FRIDAY
FOR COASTAL WATERS FROM CAPE FLATTERY TO JAMES ISLAND OUT
10 NM-COASTAL WATERS FROM JAMES ISLAND TO POINT GRENVILLE
OUT 10 NM-COASTAL WATERS FROM POINT GRENVILLE TO CAPE
SHOALWATER OUT 10 NM.
SMALL CRAFT ADVISORY FROM 8 AM THURSDAY TO 5 PM PDT FRIDAY 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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