339
FXUS66 KSEW 042155
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
255 PM PDT SAT OCT 4 2025
SYNOPSIS
SKIES WILL BEGIN TO CLEAR TONIGHT AS UPPER LEVEL
RIDGING BEGINS TO BUILD OVER THE AREA BEHIND AN EXITING SHORTWAVE
TROUGH. THIS WILL ALLOW FOR MORE CLEAR SKIES AS WELL AS WARMER
TEMPERATURES AND LOWER HUMIDITY THROUGH TUESDAY. COOLER AND
WETTER CONDITIONS LOOK TO RETURN WEDNESDAY THROUGH THE LATTER HALF
OF THE WEEK, BUT DETAILS REMAIN UNCERTAIN.
SHORT TERM /TONIGHT THROUGH TUESDAY/
MOSTLY CLOUDY SKIES
CURRENTLY PREVAIL ACROSS WESTERN WASHINGTON WITH A FEW LINGERING
SHOWERS OVER THE CASCADES THIS AFTERNOON. CLOUDS SHOULD CONTINUE
TO DECREASE IN COVERAGE THIS EVENING AS UPPER LEVEL RIDGING BEGINS
TO NOSE INTO THE REGION AS A TROUGH CONTINUES TO SLIDE TO THE
SOUTHWEST. WITH THE DECREASED CLOUD COVERAGE, EXPECT AREAS OF LOW
STRATUS TO FROM THROUGH PORTIONS OF THE AREA. SINCE LOW LEVEL
WINDS WILL BEGIN TO TURN OFFSHORE, THINKING THAT FOG WILL BE LESS
LIKELY AS THE OFFSHORE WINDS WILL HELP TO DRY OUT THE LOWEST
LEVELS. FORECASTED LOW TEMPERATURES WILL REMAIN COOL, IN THE 40S
ACROSS MOST OF THE AREA. FREEZING LEVELS WILL DIP TO AROUND
4500-5000 FT ACROSS THE NORTH CASCADES ALLOW FOR SUBFREEZING
TEMPERATURES AROUND WASHINGTON PASS.
UPPER LEVEL RIDGING WILL CONTINUE TO MOVE OVER THE AREA THROUGH
TUESDAY. THIS WILL ALLOW TEMPERATURES TO SLOWLY WARM EACH DAY.
HIGH SUNDAY WILL BE IN THE MID 60S ACROSS THE AREA, RISING TO THE
LOW TO MID 70S ON TUESDAY. THIS WILL ALSO ALLOW MINIMUM RH VALUES
TO DIP BELOW 40% ACROSS THE ENTIRE REGION, WITH SOME AREAS
REACHING BELOW 30%, PARTICULARLY ACROSS THE CENTRAL AND SOUTHERN
WA CASCADES. ADDITIONALLY, OFFSHORE FLOW WILL CONTINUE THROUGH
TUESDAY WITH A THERMAL TROUGH DEVELOPING ALONG THE COAST. WINDS
MAY REACH UP TO 15-20 MPH OVER THE CASCADES FROM MONDAY NIGHT INTO
TUESDAY MORNING. WHILE THIS IS NOT CRITICAL FIRE WEATHER
CONDITIONS, ACTIVE FIRES MAY SEE AN UPTICK IN ACTIVITY WITH A
NOTABLE CHANGE IN THE WIND DIRECTION.
LONG TERM /WEDNESDAY THROUGH SATURDAY/
MODEL SOLUTIONS ARE
STARTING TO LOOK MORE CONSISTENT ON WEDNESDAY, BRINGING THE
TROUGH INTO THE REGION FROM THE NORTHWEST. HOWEVER, PRECIPITATION
AMOUNTS WILL BE MEAGER WITH MOST OF THE AREA RECEIVING, AT MOST,
A FEW TENTHS OF AN INCH WITH STILL A SOLID PERCENTAGE OF ENSEMBLE
MEMBERS KEEPING THINGS MOSTLY DRY. AS FOR WHERE THE TROUGH GOES
THURSDAY AND BEYOND, THINGS REMAIN VERY UNCERTAIN. SOME KEEP THE
TROUGH DIRECTLY OVERHEAD, SOME (INCLUDING THE GFS) HAVE THE LOW
RETROGRADE BACK OVER THE PACIFIC, WHILE A FEW PROGRESS THE TROUGH
THROUGH INTERMOUNTAIN WEST. ENSEMBLE CLUSTER ANALYSIS REVEALS THAT
MOST ENSEMBLE MEMBERS KEEP UPPER LEVEL TROUGHING IN PLACE,
THROUGH ABOUT 10% ACTUALLY START TO REINTRODUCE ANOTHER RIDGE.
THAT BEING SAID, THE MEAN SOLUTION KEEPS TEMPERATURES SEASONABLE
(HIGHS IN THE MID TO UPPER 60S, LOWS IN THE 40S) WITH CHANCES FOR
RAIN AND SHOWERS FROM WEDNESDAY THROUGH NEXT WEEKEND.
62
AVIATION
NORTHERLY FLOW WILL CONTINUE ALOFT THROUGH THE TAF
PERIOD. LATEST RADAR SHOWS SOME LIGHT SHOWER ACTIVITY PERSISTING
ACROSS THE NORTH AND CENTRAL CASCADES THIS AFTERNOON AS A WEAK
SYSTEM MOVES ACROSS THE AREA. CONDITIONS ACROSS AREA TERMINALS
HAVE LARGELY IMPROVED AND ARE PRIMARILY VFR TO MVFR. FOR MVFR
TERMINALS (EXCEPT HQM ON THE COAST), EXPECT CEILINGS TO CONTINUE
TO IMPROVE TOWARDS VFR INTO THE EVENING HOURS. WINDS PRIMARILY
PERSIST OUT OF THE NORTH BETWEEN 4-8 KT. WINDS WILL EASE SOMEWHAT
OVERNIGHT, BEFORE SHIFTING MORE NE AND INCREASING TO 7-12 KT
AGAIN BETWEEN 14-18Z. CEILINGS WILL LOWER TOWARDS MVFR AGAIN
OVERNIGHT, LIKELY BETWEEN 12-15Z, WITH IMPROVEMENT TOWARDS VFR
EXPECTED AGAIN BY 18-21Z.
KSEA...VFR CONDITIONS WITH WINDS OUT OF THE NW PERSISTING AT 4-8
KT. GUIDANCE HINTS AT ROUGHLY A 35 PERCENT CHANCE OF CEILINGS
LOWERING BACK DOWN TO MVFR BETWEEN 12-15Z. WINDS WILL WEAKEN
SLIGHTLY OVERNIGHT BEFORE SHIFTING TO THE NE AND INCREASING TO
7-12 KT BETWEEN 14-18Z.
14
MARINE
A WEAK FRONTAL SYSTEM WILL CONTINUE TO MAKE ITS WAY ACROSS
THE REGION TONIGHT, WITH NO SIGNIFICANT IMPACTS EXPECTED ACROSS
THE AREA WATERS. A BROAD AREA OF HIGH PRESSURE WILL THEN BUILD
BACK ACROSS THE COASTAL WATERS IN ITS WAKE, WHILE A THERMAL TROUGH
BUILDS NORTHWARD ALONG THE COAST SUNDAY THROUGH TUESDAY. ONSHORE
FLOW WILL SWITCH TO OFFSHORE ACROSS THE AREA WATERS AS A RESULT.
SEAS ACROSS THE COASTAL WATERS WILL PRIMARILY HOVER BETWEEN 3-6
FT. A WEAKENING FRONTAL SYSTEM WILL THEN MOVE OVER THE AREA WATERS
ON TUESDAY, ALLOWING FOR WINDS TO SWITCH BACK TO ONSHORE. A PUSH
OF WESTERLY WINDS IS LIKELY DOWN THE CENTRAL AND EAST STRAIT OF
JUAN DE FUCA TUESDAY EVENING IN ITS WAKE, WITH SEAS BUILDING TO
8-10 FT ACROSS THE COASTAL WATERS. ADDITIONAL WEAK SYSTEMS MAY
MOVE ACROSS THE AREA WATERS LATE IN THE WEEK.
14
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...NONE.
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