918
FXUS66 KSEW 031634
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
934 AM PDT FRI OCT 3 2025
SYNOPSIS
GENERALLY DRY CONDITIONS THROUGH LATE THIS AFTERNOON
BEFORE A WEAK SYSTEM BRUSHES PAST THE AREA, ALLOWING FOR A CHANCE OF
SHOWERS TONIGHT AND SATURDAY. UPPER LEVEL RIDGING BUILDS IN STARTING
SUNDAY, WARMING TEMPERATURES AND RETURNING DRY CONDITIONS TO THE
AREA FOR AT LEAST THE FIRST HALF OF NEXT WEEK. ADDITIONAL SYSTEMS
ARE POSSIBLE LATE IN THE WEEK, BUT CONFIDENCE REMAINS LOW.
SHORT TERM /TODAY THROUGH SUNDAY/
THE LATEST FORECAST REMAINS
ON TRACK WITH NO UPDATES THIS MORNING. AREAS OF PATCHY FOG WILL
CONTINUE TO ERODE THROUGHOUT THE MORNING, LEADING TO DRY AND
PARTLY CLOUDY CONDITIONS BY THE AFTERNOON.
CURRENT GENERALLY DRY CONDITIONS ARE EXPECTED TO PERSIST
THROUGHOUT MUCH OF THE DAY BEFORE A WEAK SHORTWAVE DIPS INTO THE
AREA ALONG THE LEADING EDGE OF A BUILDING UPPER LEVEL RIDGE OUT
OVER THE PACIFIC. WHILE THIS FEATURE HAS BEEN PERSISTENT IN MODEL
SOLUTIONS FOR THE PAST FEW DAYS, NBM SEEMS TO HAVE REALLY RAMPED
UP THE POPS OVER THE AREA FOR TONIGHT AND MUCH OF SATURDAY IN THE
LATEST SOLUTIONS. CONSULTING BOTH DETERMINISTIC AND ENSEMBLE
MODELS, THIS SYSTEM LOOKS PALTRY AT BEST...PERHAPS A HIGH POP/LOW
QPF SORT OF EVENT...BUT CONFIDENCE IN POPS HIGHER THAN 60 PCT JUST
SIMPLY IS NOT THERE ASIDE FROM IN THE CASCADES WHERE THE TERRAIN
MAY PROVE TO BE OF ASSISTANCE WHEN IT COMES TO SHOWER DEVELOPMENT.
THAT SAID, DID MAKE SOME CUTS TO THE FORECAST, KEEPING POPS AT
MOST HIGH-END CHANCE WORDING /50-60 PCT/ THUS MAINTAINING
COLLABORATION WITH SURROUNDING OFFICES AS WELL AS SPLITTING THE
DIFFERENCE BETWEEN FORECASTER AND MODEL EXPECTATIONS.
SUNDAY SEES W WA UNDER THE FULL THRALL OF THE UPPER RIDGE OFF TO THE
WEST, WITH A RETURN TO DRY CONDITIONS AS EARLY AS LATE SATURDAY
NIGHT. THIS WILL ALSO BE THE FIRST DAY OF A WARMING TREND, BRINGING
DAYTIME HIGHS INTO THE MID 60S FOR INTERIOR LOWLAND LOCATIONS, JUST
A FEW DEGREES WARMER THAN SEASONAL AVERAGES.
18
LONG TERM /MONDAY THROUGH THURSDAY/
THE AFOREMENTIONED UPPER
LEVEL RIDGE WILL REMAIN THE MAIN DRIVER FOR W WA WEATHER FOR AT
LEAST MONDAY AND TUESDAY AS THE FEATURE MOVES EASTWARD, BROADENING
AS IT DOES SO. BEYOND THIS POINT, CONFIDENCE DROPS OFF FAST AS
MODELS CONTINUE TO OFFER DIFFERING SOLUTIONS. DETERMINISTIC GFS
KEEPS THE RIDGE STRONG ENOUGH TO KEEP THE NEXT UPPER LEVEL TROUGH
OUT OVER THE PACIFIC WATERS WHILE DETERMINISTIC ECMWF HAS SAID
TROUGH PUSH THE RIDGE FURTHER EASTWARD, BRINGING RAIN BACK TO THE
PAC NW. ENSEMBLES APPEAR TO FAVOR THE ECMWF SOLUTION TO VARYING
DEGREES AND THE NBM HAS LATCHED ONTO THAT. THE AMOUNT OF MOISTURE IN
PLAY HOWEVER CONTINUES TO BE THE DIVIDING POINT AND AS SUCH KEEPS
CONFIDENCE LOW AS THE TRACK OF SAID TROUGH WILL MAKE A SIGNIFICANT
DIFFERENCE IN HOW MUCH PRECIP THE AREA RECEIVES...IF IT GETS ANY AT
ALL.
THE LONG TERM PERIOD WILL START OF WITH CONTINUED WARMING
TEMPERATURES, WITH LOWER 70S EXPECTED EACH DAY FOR INTERIOR
LOWLANDS. THE SWITCH TO A MORE TROUGHY PATTERN WILL ALLOW CONDITIONS
TO COOL CLOSER TO SEASONAL NORMALS FOR THE REMAINDER OF THE FORECAST
PERIOD, LOWER TO MID 60S. OF COURSE, HEWING CLOSER TO NORMAL MAY
ALSO BE INDICATIVE OF THE LOWER CONFIDENCE IN THIS PORTION OF THE
FORECAST...BUT LIKELY THE BEST ROUTE TO TAKE AT THIS TIME.
18
AVIATION
SOUTHWESTERLY FLOW ALOFT BECOMING NORTHWESTERLY TONIGHT
AS A TROUGH MOVES OVER THE REGION. MANY LOCATIONS EXPERIENCING LIFR
CONDITIONS UNDER FOG. EXPECTING THE FOG TO QUICKLY LIFT AND SCATTER
THIS MORNING AS THE SUN CONTINUES TO RISE. AFTER THE FOG LIFTS,
EXPECT VFR CONDITIONS THROUGH THE REST OF THE DAY WITH INCREASING MID
AND HIGH LEVEL CLOUDS. A DECAYING FRONTAL SYSTEM WILL PUSH THROUGH
THE TERMINALS FRIDAY NIGHT INTO SATURDAY MORNING. IT WILL BRING
LIGHT RAIN AND WIDESPREAD MVFR CEILINGS. LIGHT TO CALM WINDS EARLY
THIS MORNING WILL BECOME MORE SW LATER THIS MORNING INTO THE
AFTERNOON AT 3-5 KT.
KSEA...LIFR CONDITIONS THIS MORNING IN FOG. SMALL IMPROVEMENTS WILL
COME AND GO BEFORE THE FOG FINALLY LIFTS AND EVAPORATES IN A FEW
HOURS THIS MORNING. IMPROVEMENT EXPECTED AFTER 18Z INTO VFR FOR THE
REST OF THE DAY. A WEAKENING FRONTAL SYSTEM WILL LIKELY BRING MVFR
CEILINGS FRIDAY NIGHT INTO SATURDAY MORNING. IT IS POSSIBLE CEILINGS
MAY LOWER INTO IFR (45% CHANCE) AND LIFR (20% CHANCE). RAIN WILL BE
LIGHT. LIGHT S/SE WINDS EARLY THIS MORNING WILL BECOME MORE SW BY
FRIDAY EARLY AFTERNOON AT 5-6 KT. WINDS THEN SHIFT MORE WSW FRIDAY
EVENING.
29/62
MARINE
A WEAKENING FRONTAL SYSTEM WILL MOVE OVER THE WATERS
FRIDAY INTO SATURDAY. BROAD SURFACE HIGH PRESSURE WILL CONTINUE
BUILDING OVER AREA WATERS INTO THE WEEKEND AND INTO EARLY NEXT WEEK,
MAINTAINING NORTHERLY SURFACE WINDS OVER AREA WATERS. BENIGN MARINE
CONDITIONS LIKELY TO CONTINUE INTO MONDAY. A SURFACE TROUGH WILL
MOVE OVER THE COASTAL WATERS ON TUESDAY EVENING, BRINGING INCREASED
WINDS TO THE COASTAL WATERS. LATEST GUIDANCE SUGGESTS SUSTAINED
WINDS HAVE A 25-40% CHANCE OF EXCEEDING 21 KT. COMBINED SEAS
GENERALLY 4-6 FT INTO THE WEEKEND. SEAS WILL BUILD TUESDAY EVENING
TO 6-8 FT.
29
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...NONE.
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