940
FXUS66 KSEW 090426
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
926 PM PDT WED OCT 8 2025
UPDATE
AN UPPER LEVEL LOW CONTINUES TO DIG SOUTHWARD OVER THE
OFFSHORE WATERS THIS EVENING WITH INCREASING SOUTHERLY FLOW ALOFT
OVER WESTERN WASHINGTON. SHOWER ACTIVITY HAS BEEN PRIMARILY OVER
THE HIGHER TERRAIN OF THE CASCADES THUS FAR, BUT WE'LL SEE THE
FOCUS POINT OF THE PRECIP SHIFT WESTWARD TOWARD MORNING AS THE
UPPER LOW DIGS SOUTHWARD AND ANOTHER UPPER DISTURBANCE ROTATES
ONSHORE. TRENDS LOOK GOOD IN CURRENT FORECASTS WITH NO UPDATES
ANTICIPATED THIS EVENING. PREVIOUS DISCUSSION FOLLOWS WITH UPDATE
TO AVIATION SECTION. 27
SYNOPSIS
A DEEP UPPER LOW OFFSHORE WILL LINGER ALONG THE
WEST COAST THROUGH FRIDAY, RESULTING IN PERIODIC SHOWERS. UPPER
TROUGHING WILL BE REINFORCED OVER THE PACIFIC NORTHWEST OVER
THE WEEKEND INTO EARLY NEXT WEEK WITH COOLER TEMPERATURES AND
CONTINUED UNSETTLED WEATHER.
SHORT TERM /TODAY THROUGH FRIDAY/
DRIER WEATHER CONTINUES
THIS AFTERNOON WITH A MIX OF CLOUDS AND SUNSHINE AS AN UPPER LOW
DEEPENS OFFSHORE OF THE PACIFIC NORTHWEST. THE UPPER LOW WILL BE
SITUATED OFFSHORE OF THE OREGON COAST TONIGHT INTO FRIDAY AND BE
THE PRIMARY WEATHER FEATURE OVER THE NEXT FEW DAYS. GIVEN THE
POSITION OF THE UPPER LOW, SOUTH-SOUTHEASTERLY FLOW ALOFT WILL
INCREASE TONIGHT. SHOWERS ARE INITIALLY EXPECTED TO DEVELOP OVER
THE OREGON & WASHINGTON CASCADES LATER THIS EVENING, AND MOVE
NORTHWARDS INTO THURSDAY MORNING. DESPITE THE CONVECTIVE NATURE OF
THE PRECIPITATION, THUNDERSTORM CHANCES TONIGHT INTO THURSDAY
REMAIN LIMITED DUE TO A LACK OF INSTABILITY. ANOTHER ROUND OF
SHOWERS ARE EXPECTED AGAIN THURSDAY NIGHT INTO FRIDAY. ALTHOUGH
MUCAPE VALUES ARE LIMITED FRIDAY (LESS THAN 100 J/KG), WILL NEED
TO MONITOR ANY EMBEDDED THUNDERSTORM IN SHOWERS, AND AS SUCH A
GENERAL THUNDERSTORM RISK HAS BEEN INCLUDED FOR PORTIONS OF
WESTERN WASHINGTON FROM STORM PREDICTION CENTER. OTHERWISE, THERE
WILL BE BREAKS IN PRECIPITATION, PARTICULARLY EACH AFTERNOON, WITH
SOME SUNSHINE AS WELL. TEMPERATURES WILL BE NEAR NORMAL THROUGH
FRIDAY, WITH HIGHS IN THE UPPER 50S TO MID 60S.
LONG TERM /SATURDAY THROUGH WEDNESDAY/
THE AFOREMENTIONED
UPPER LOW OFFSHORE WILL MOVE INLAND OVER OREGON ON SATURDAY.
DURING THIS TIME, TROUGHING WILL BE REINFORCED OVER WESTERN
WASHINGTON AS AN UPPER LOW DIVES SOUTHWARDS OUT OF BC AND
DEEPENS ACROSS THE PACIFIC NORTHWEST SUNDAY. ALTHOUGH THERE IS
SOME UNCERTAINTY INTO THE LOCATION OF THE UPPER LOW BY TUESDAY
NEXT WEEK, THE UPPER LOW LOOKS TO CONTINUE TO DEEPEN TOWARDS
CALIFORNIA. THIS WILL RESULT IN UNSETTLED WEATHER SATURDAY
THROUGH AT LEAST MONDAY FOR WESTERN WASHINGTON. FURTHERMORE,
TEMPERATURES WILL ALSO BECOME SIGNIFICANTLY COOLER SUNDAY INTO
MONDAY, ESPECIALLY OVER THE MOUNTAINS. SNOW LEVELS INITIALLY
AROUND 6000 FEET EARLY SATURDAY WILL FALL TO 3000 TO 4000 FEET
BY MONDAY. HIGHER ELEVATION MOUNTAIN SNOWFALL IS EXPECTED DURING
THIS PERIOD. AT THIS TIME, NBM PROBABILITIES OF 3" OF SNOW (72
HOURS ENDING TUESDAY) RANGES 80 TO 95% FOR RAINY PASS AND
PARADISE, WITH PROBABILITIES OF 50 TO 75% FOR STEVENS PASS AND
HEATHER MEADOWS. FOR THOSE HEADING INTO THE HIGHER ELEVATIONS
OF THE CASCADES AND OLYMPICS SATURDAY INTO MONDAY, CONTINUE TO
MONITOR THE WEATHER FORECAST, AND PREPARE FOR SNOW AND MUCH
COOLER TEMPERATURES.
PRECIPITATION POTENTIAL BEGINS TO TAPER OFF LATE MONDAY INTO
MIDWEEK AS THE UPPER LOW CONTINUES TO DEEPEN SOUTHWARDS INTO
CALIFORNIA. OVERNIGHT TEMPERATURES EARLY NEXT WEEK MAY DIP INTO
THE 30S FOR AREAS AWAY FROM THE WATER, AND AS SUCH WILL NEED TO
MONITOR ANY FROST POTENTIAL. OTHERWISE, HIGH TEMPERATURES WILL
TREND A FEW DEGREES BELOW NORMAL EARLY NEXT WEEK. JD
AVIATION
UPPER LEVEL LOW REMAINING OFF THE COAST THROUGH
THURSDAY WITH SOUTH SOUTHEASTERLY FLOW ALOFT. LIGHT FLOW IN THE
LOWER LEVELS.
MIDDLE AND HIGH LEVEL CLOUDS OVER THE AREA WITH CEILINGS AOA 12000
FEET THROUGH EARLY THURSDAY MORNING AND AGAIN THURSDAY AFTERNOON.
BAND OF MOISTURE ROTATING AROUND THE LOW MOVING THROUGH THE AREA
09Z-19Z WITH SCATTERED SHOWERS AND CEILINGS 4000-5000 FEET.
KSEA...MIDDLE AND HIGH LEVEL CLOUDS INTO THE EARLY MORNING HOURS.
CEILINGS LOWERING TO 4000-5000 FEET AROUND 09Z AND REMAINING IN
THAT RANGE THROUGH THE MORNING. CEILINGS IMPROVING TO AOA 10000
FEET THURSDAY AFTERNOON. VARIABLE MOSTLY NORTHERLY WIND LESS THAN
6 KNOTS. FELTON
MARINE
A WEATHER SYSTEM WILL BE LOCATED OFFSHORE OF OREGON
INTO FRIDAY. PERIODIC SHOWERS MAY RESULT IN ELEVATED WINDS AT
TIMES, PARTICULARLY FOR THE COASTAL WATERS ON THURSDAY. ALTHOUGH
SOUTHEAST WINDS FOR THE COAST ARE EXPECTED TO REMAIN BELOW SMALL
CRAFT ADVISORY THRESHOLD ON THURSDAY, BRIEF SCA WIND GUSTS ARE
POSSIBLE. OTHERWISE, THE WEATHER SYSTEM OFFSHORE WILL MOVE
INLAND AND WEAKEN ON FRIDAY. A SECONDARY WEATHER SYSTEM WILL
THEN DEVELOP OVER THE AREA SATURDAY, RESULTING IN INCREASED
WINDS. SCA WINDS FOR THE COASTAL WATERS AND STRAIT OF JUAN DE
FUCA ARE EXPECTED SATURDAY INTO EARLY SUNDAY. THERE ALSO REMAINS
A 40 TO 70% CHANCE OF GALE FORCE WIND GUSTS FOR THESE AREAS.
WINDS THEN LOOK TO TRANSITION MORE NORTHEASTERLY EARLY NEXT
WEEK.
SEAS OF 6 TO 8 FEET INTO TONIGHT WILL SUBSIDE TO 4 TO 6 FEET ON
FRIDAY. SEAS THEN WILL BUILD TO NEAR 12 TO 16 FEET OVER THE
WEEKEND ASSOCIATED WITH THE WEATHER SYSTEM. DOMINANT PERIOD OF 9
TO 12 SECONDS WILL CONTINUE THROUGH FRIDAY. JD
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...NONE.
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