365
FXUS66 KSEW 210351
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
851 PM PDT TUE OCT 20 2026
SYNOPSIS
DRY WITH WARMER THAN NORMAL DAYTIME TEMPS WILL LINGER THROUGH
WEDNESDAY. A WEAK SYSTEM THURSDAY WILL BRING INCREASED CLOUDS,
NEAR NORMAL TEMPERATURES AND A FEW LIGHT SHOWERS. DRY AND
CONTINUED NEAR NORMAL TEMPERATURES FRIDAY, FOLLOWED BY A CHANCE
OF A WEAK SYSTEM OVER THE WEEKEND.
SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/
NO CHANGES TO THE FORECAST THIS EVENING. DRY WITH NEAR-NORMAL
TO SLIGHTLY COOLER THAN NORMAL OVERNIGHT LOWS TONIGHT. LIGHTER
WINDS INTO WEDNESDAY MORNING WILL ALLOW FOR MORE EARLY MORNING
PATCHY FOG FORMATION IN SHELTERED LOCATIONS. MORNING SHALLOW
STRATUS/FOG SHOULD LIFT AND SCATTER LATE MORNING WITH ANOTHER
WARM OCTOBER DAY. A WEAK UPPER LEVEL SYSTEM CONTINUES TO BE
EXPECTED TO BRUSH THE AREA THURSDAY. THE MAIN IMPACT WILL BE
MORE CLOUD COVER AND NEAR NORMAL TEMPERATURES. HIGH RESOLUTION
ENSEMBLES LIKE THE REFS SHOWING VERY LIMITED, SHORTLIVED SHOWERS
MAINLY IN THE OLYMPICS AND NORTH CASCADES THURSDAY AFTERNOON
AND EVENING.
LONG TERM /FRIDAY THROUGH TUESDAY/
ENSEMBLES IN FAIR ALIGNMENT WITH THE OVERALL PATTERN FRIDAY
BECOMING MORE ZONAL BUT DRY FRIDAY. FOR THE WEEKEND, ENSEMBLE
CLUSTERS IN GOOD AGREEMENT WITH THE OVERALL PATTERN INDICATING
AN UPPER LEVEL TROUGH MOVING ACROSS THE NE PACIFIC AND GULF OF
ALASKA FRIDAY NIGHT, THEN SHEARING INTO A MORE CONSOLIDATED
TROUGH MOVING INTO BRITISH COLUMBIA SATURDAY AND A TRAILING
UPPER LEVEL LOW OVER THE EASTERN PACIFIC. THE GRAND ENSEMBLE
SHOWING GOOD AGREEMENT ON THE OVERALL IDEA OF THIS UPPER LEVEL
TROUGH MOVING SOUTH AND EAST THROUGH BRITISH COLUMBIA ITSELF OR
ALONG WEST ALONG THE BC INTO WESTERN WASHINGTON SATURDAY NIGHT
INTO SUNDAY. NEARLY HALF (48%) OF THE ENSEMBLE MEMBERS FAVOR
THE MORE DIRECT APPROACH WITH A MORE CONSOLIDATED TROUGH. THE
REMAINING 52% SHOW EITHER SLOWER MORE NORTHERLY TRACK OR EVEN
OFFSHORE TRACK FOR THE TROUGH. THE MORE CONSOLIDATED TRACK WOULD
RESULT IN A MORE ORGANIZED, BUT LIKELY WEAK SYSTEM MOVING
THROUGH THE AREA SATURDAY NIGHT INTO SUNDAY, WHERE THE
NORTHERLY/OFFSHORE SCENARIOS WOULD LIKELY RESULT IN MORE LIMITED
PRECIPITATION BRUSHING THE AREA SUNDAY OR EVEN DELAYED INTO
MONDAY. THE OVERALL PATTERN EARLY NEXT WEEK LOOKS FAIRLY EVENLY
SPLIT WITH 49% OF THE GRAND ENSEMBLE SHOWING SOME DEGREE OF
RIDGING EARLY IN THE WEEK, AND 51% SOME DEGREE OF TROUGHING.
AVIATION
AN UPPER LEVEL LOW CONTINUES TO SPIN OFF CA WITH DRY
AND STABLE CONDITIONS ACROSS WESTERN WA. THE FLOW ALOFT IS
SOUTHWESTERLY. VFR CONDITIONS WILL CONTINUE THIS EVENING. PATCHY,
SHALLOW, FOG WILL LIKELY DEVELOP IN THE INTERIOR WEDNESDAY MORNING
FOR A BRIEF PERIOD OF LIFR CONDITIONS. FOG WILL SCATTER OUT BY 18-
20Z FOR A RETURN OF VFR CONDITIONS. LIGHT NORTHERLY SURFACE
WINDS AROUND 5 KT OR LESS WILL PREVAIL WEDNESDAY AFTERNOON IN
THE INTERIOR. 33/29
KSEA...
VFR CONDITIONS TONIGHT. A BRIEF PERIOD OF SHALLOW/PATCHY FOG
IS POSSIBLE EARLY WEDNESDAY MORNING FOR LIFR CONDITIONS.
OTHERWISE, VFR EXPECTED BY THE AFTERNOON AFTER 18Z. NE WINDS
WILL CONTINUE TO EASE TONIGHT TO AROUND 5 KT, THEN LIGHT AND
VARIABLE WEDNESDAY MORNING. WINDS WEDNESDAY AFTERNOON WILL BE
MORE W TO NW AROUND 5 KT, THE BECOMING NE IN THE EVENING. 33/29
MARINE
WEAK HIGH PRESSURE WILL LEAD TO GENERALLY LIGHT WINDS
OVER THE WATERS THROUGH WEDNESDAY. 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.
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
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...NONE.
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