650
FXUS66 KSEW 181622
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
922 AM PDT FRI APR 18 2025
UPDATE
FORECAST ON TRACK THIS MORNING. UPPER LEVEL RIDGE AXIS
OVER WESTERN WASHINGTON. WHILE TEMPERATURES ARE ONLY SLIGHTLY
WARMER AT 9 AM VERSUS YESTERDAY THE LACK OF NORTHERLY WINDS WILL
HELP TEMPERATURES WARM MORE THIS AFTERNOON. HIGHS IN THE 60S TO
LOWER 70S. WEAK UPPER LEVEL TROUGH NOW APPROACHING THE NORTHERN
END OF VANCOUVER ISLAND REACHING THE AREA SATURDAY MORNING. NOT
MUCH IN THE WAY OF PRECIPITATION WITH THIS FEATURE. MAIN RESULT
WILL BE TO USHER COOLER AIR INTO THE AREA. HIGHS SATURDAY IN THE
MID 50S TO LOWER 60S. NO UPDATE THIS MORNING. PREVIOUS DISCUSSION
FOLLOWS WITH UPDATED AVIATION AND MARINE SECTIONS.
SYNOPSIS
AN UPPER RIDGE WILL MAINTAIN DRY, WARM CONDITIONS
TODAY. A WEAK FRONTAL SYSTEM WILL BRING SHOWERS FRIDAY NIGHT
THROUGH SATURDAY. UPPER TROUGHING WILL BE OVER THE PACIFIC
NORTHWEST SUNDAY INTO MONDAY FOR CONTINUED UNSETTLED WEATHER.
WEAK TROUGHING ON TUESDAY WITH RIDGING WEDNESDAY INTO THURSDAY.
SHORT TERM /TODAY THROUGH SUNDAY/
GENERALLY CLEAR SKIES EARLY
THIS MORNING ACROSS WESTERN WASHINGTON WITH A FEW HIGH CLOUDS.
ANOTHER DRY, WARM DAY FOR THE AREA WITH THE UPPER RIDGE AXIS OVER
PACIFIC NORTHWEST. TEMPERATURES WILL PEAK THIS AFTERNOON IN THE
MID 60S TO LOWER 70S. CLOUDS INCREASE LATER THIS AFTERNOON INTO
THIS EVENING AS ONSHORE FLOW INCREASES AHEAD OF A WEAK FRONT.
SHOWERS WILL INITIALLY MOVE EASTWARD ACROSS THE OLYMPIC PENINSULA
EARLY TONIGHT, BEFORE MOVING INTO THE INTERIOR AND CASCADES
SATURDAY MORNING. ONSHORE FLOW WILL THEN PROMOTE THE DEVELOPMENT
OF WEAK CONVERGENCE ACROSS CENTRAL PUGET SOUND FOR A FEW SHOWERS
LINGERING INTO SATURDAY AFTERNOON. TEMPERATURES WILL BE COOLER ON
SATURDAY, WITH HIGHS IN THE MID 50S TO LOW 60S.
TROUGHING WILL THEN SLIDE SOUTHWARDS FROM BRITISH COLUMBIA INTO
THE PACIFIC NORTHWEST ON SUNDAY, ALLOWING FOR ANOTHER UPTICK IN
PRECIPITATION POTENTIAL FOR WESTERN WASHINGTON ON SUNDAY. ANOTHER
CONVERGENCE ZONE WILL LIKELY DEVELOP AROUND KING AND SNOHOMISH
COUNTIES SUNDAY EVENING INTO SUNDAY NIGHT FOR ADDITIONAL
PRECIPITATION. SNOW LEVELS BY SUNDAY NIGHT WILL FALL TO NEAR 2500
TO 3000 FEET, RESULTING IN A FEW INCHES OF SNOWFALL IN THE
CENTRAL CASCADES, INCLUDING THE PASSES. TEMPERATURES WILL CONTINUE
TO BE COOLER ON SUNDAY, WITH HIGHS IN THE 50S.
LONG TERM /MONDAY THROUGH THURSDAY/
THE UPPER TROUGH WILL
SLOWLY SLIDE EASTWARDS ON MONDAY, WITH LINGERING PRECIPITATION
TAPERING OFF BY LATER MONDAY. WEAK TROUGHING IS EXPECTED TO
DEVELOP OVER WESTERN WASHINGTON ON TUESDAY, ALTHOUGH NOT MUCH IN
THE WAY OF PRECIPITATION IS EXPECTED ON TUESDAY. ENSEMBLES ARE IN
GENERAL AGREEMENT THAT WEAK RIDGING WILL BUILD WEDNESDAY INTO
THURSDAY FOR DRIER WEATHER. OVERNIGHT TEMPERATURES BOTH TUESDAY
AND WEDNESDAY MORNING WILL BE ON THE COOLER SIDE, FROM THE MID 30S
TO LOW 40S, AND WILL HAVE TO MONITOR ANY FROST POTENTIAL. HIGH
TEMPERATURES WILL SLOWLY MODERATE THROUGH MIDWEEK AS RIDGING
BUILDS INTO THE AREA. JD
AVIATION
AN UPPER LEVEL RIDGE AXIS WILL TRAVERSE THE AREA THIS
MORNING, FOLLOWED QUICKLY BY A SUBTLE SHORTWAVE TROUGH MOVING
THROUGH OVERNIGHT INTO SATURDAY MORNING, WITH WINDS PRIMARILY W/NW.
VFR CONDITIONS PREVAIL TODAY. MVFR CONDITIONS BEGIN TO DEVELOP THIS
EVENING ALONG THE COAST AHEAD OF AN INCOMING FRONT, THOUGH NOT
REACHING THE INTERIOR TERMINALS UNTIL SATURDAY MORNING AFTER 12Z
ONCE THE FRONT BEGINS TO MOVE ONSHORE. NO SIGNIFICANT PRECIPITATION
IS EXPECTED.
MOST TERMINALS SEEING CALM TO LIGHT SOUTHEAST WINDS THIS MORNING
BEFORE SHIFTING TO MORE SOUTHWESTERLY LATER THIS MORNING THEN
INCREASING IN SPEED TO 5-10 KTS. A WESTERLY PUSH DOWN THE STRAIT OF
JUAN DE FUCA THIS AFTERNOON WILL ALLOW FOR WINDS REACHING 10-15 KT
WITH GUSTS UP TO 20-25 KT POSSIBLE AT CLM.
KSEA...VFR CONDITIONS WITH SOME HIGH CIRRUS. LIGHT AND VARIABLE
WINDS WITH SPEEDS 5 KTS OR LESS THIS MORNING WILL SWITCH TO
SOUTHWEST AROUND 15Z, WITH SPEEDS INCREASING TO 6 TO 10 KT. WINDS
COULD BRIEFLY SWITCH TO N/NE AS EARLY AS AROUND 03Z SATURDAY, BUT
LOOKS MORE LIKELY AFTER AROUND 06-09Z SATURDAY.
18/62
MARINE
SURFACE RIDGING WILL REMAIN OVER THE WATERS TODAY BEFORE
A WEAK FRONT SLIPS SOUTHWARD ALONG THE BRITISH COLUMBIA COAST AND
INTO AREA WATERS TONIGHT INTO SATURDAY. INCREASING NORTHWESTERLIES
OVER THE COASTAL WATERS AND STRENGTHENING ONSHORE FLOW WILL BRING
SOLID SMALL CRAFT CONDITIONS TO MANY AREA WATERS. INHERITED HEADLINE
LOOKS GOOD AND WILL REMAIN UNALTERED WITH THE MORNING FORECAST
PACKAGE.
SEAS 5 TO 7 FT TODAY BUILDING TO ABOVE 10 FEET LATE TONIGHT INTO
SATURDAY. IN ADDITION, STEEP SEAS POSSIBLE WITH PERIODS UNDER 10
SECONDS OVER THE COASTAL WATERS INTO SATURDAY. A SECONDARY SYSTEM
WILL PRODUCE A SIMILAR RESULT LATER SUNDAY INTO EARLY MONDAY. HIGH
PRESSURE WILL THEN REBUILD ACROSS THE WATERS EARLY NEXT WEEK.
45/18
HYDROLOGY
NO RIVER FLOODING THE NEXT 7 DAYS.
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...SMALL CRAFT ADVISORY UNTIL MIDNIGHT PDT TONIGHT FOR CENTRAL U.S.
WATERS STRAIT OF JUAN DE FUCA.
SMALL CRAFT ADVISORY FROM 3 PM THIS AFTERNOON TO 5 AM PDT
SATURDAY FOR EAST ENTRANCE U.S. WATERS STRAIT OF JUAN DE
FUCA.
SMALL CRAFT ADVISORY FROM 6 PM THIS EVENING TO 6 AM PDT SATURDAY
FOR ADMIRALTY INLET-NORTHERN INLAND WATERS INCLUDING THE
SAN JUAN ISLANDS.
SMALL CRAFT ADVISORY FROM 8 PM THIS EVENING TO NOON PDT SATURDAY
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 3 PM THIS AFTERNOON TO 6 PM PDT
SATURDAY 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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