929
FXUS66 KSEW 190917
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
217 AM PDT SAT APR 19 2025
SYNOPSIS
A WEAK UPPER LEVEL TROUGH WILL MOVE THROUGH THE REGION
THIS MORNING. A COOLER, STRONGER, TROUGH ARRIVING SUNDAY FOR MORE
WIDESPREAD SHOWER ACTIVITY. POST TROUGH CONVERGENCE ZONE COULD
GIVE STEVENS OR SNOQUALMIE PASS A COUPLE INCHES OF SNOW SUNDAY
EVENING. NORTHWESTERLY FLOW ALOFT MONDAY FOR DRY AND COOLER
WEATHER. DRY WEATHER INTO MIDWEEK WITH HIGH PRESSURE.
SHORT TERM /TODAY THROUGH MONDAY/
A WEAK FRONT WILL PASS
THROUGH WESTERN WA EARLY THIS MORNING WITH LIGHT RAINFALL OVER THE
REGION. MOST AREAS WILL JUST SEE A TRACE TO A FEW HUNDREDTHS.
WE'RE UNDER POST-FRONTAL ONSHORE FLOW THROUGH THE REMAINDER OF THE
DAY LEADING TO COOLER CONDITIONS AND HIGHS IN THE 50S TO AROUND
60.
ONSHORE FLOW WILL PERSIST INTO SUNDAY AND SHOWERS WILL INCREASE
WITH A PASSING TROUGH AXIS. MOST OF THE SHOWERS WILL BE ALONG THE
COAST AND MOUNTAINS, WITH THE FOCUS SHIFTING TO THE CENTRAL SOUND
AND CASCADES SUNDAY AFTERNOON/EVENING AS A PUGET SOUND
CONVERGENCE ZONE DEVELOPS. SNOW LEVELS WILL START AROUND 4000 FT
AND WILL LOWER TO AROUND 2500 FT OVERNIGHT WITH A FEW INCHES OF
SNOW EXPECTED AT BOTH STEVENS AND SNOQUALMIE PASS.
MONDAY WILL BE DRIER BUT ALSO COOLER UNDER NW FLOW. FORECAST
HIGHS ARE IN THE 50S WITH LOWS MONDAY NIGHT IN THE 30S TO LOWER
40S. AREAS AROUND THE SOUTH SOUND MAY SEE FREEZING TEMPS WITH LOWS
IN THE LOWER 30S POSSIBLE. 33
LONG TERM /TUESDAY THROUGH FRIDAY/
HIGH PRESSURE KEEPS WESTERN
WA DRY AND MILD MOVING FORWARD NEXT WEEK. TEMPERATURES WILL PEAK
ON THURSDAY WITH HIGHS REACHING THE UPPER 60S IN THE INTERIOR.
ONSHORE FLOW WILL KEEP THE COAST A FEW DEGREES COOLER (AROUND 60).
ON FRIDAY, THE RIDGE SHIFTS EAST WHILE A TROUGH DIGS OFFSHORE. THE
TROUGH MAY PULL SOME MOISTURE NORTH FOR A CHANCE OF SHOWERS AND
COOLER CONDITIONS. 33
AVIATION
A QUICK TROUGH THIS MORNING WILL SWING A COLD FRONT
THROUGH THE REGION. THE FLOW ALOFT WILL WEAKEN FROM SOUTHWESTERLY TO
WESTERLY THROUGH SUNDAY AS THE TROUGH BROADENS OUT OVER WESTERN WA,
BEFORE PICKING BACK UP FROM THE NORTHWEST AS HIGH PRESSURE BUILDS
IN.
RADAR WAS SHOWING A LINE OF RAIN SHOWERS MOVING ACROSS ALL
TERMINALS THIS MORNING, REACHING PUGET SOUND JUST SHY OF 09Z. THE
SHOWERS HAVE BEEN LIGHT (NOT REACHING THE GROUND IN SOME SPOTS), BUT
CEILINGS HAVE BEGUN TO DROP TO MVFR ALONG THE COAST UNDER THE FRONT
(IT REMAINS COMFORTABLY VFR THIS MORNING ELSEWHERE). HI-RES GUIDANCE
HAS THE LINE BREAKING UP AS IT APPROACHES THE CASCADES JUST BEFORE
SUNRISE (~12Z). A FEW OF THE MODEL MEMBERS KEEP A CONVERGENCE ZONE
GOING THROUGH LATE THIS MORNING IN AND AROUND PUGET SOUND. FEW LOWER
CEILINGS DOWN TO MVFR ARE POSSIBLE WITH THIS, AS ARE POSSIBLE WIND
SHIFTS AND AN ISOLATED GUST TO 20 KT. ANY CONVERGENCE ZONE ACTIVITY
IS EXPECTED TO WRAP UP ~18Z, WITH SOME PARTIAL CLEARING TAKING PLACE
IN THE SOUTH SOUND LATER TODAY.
CEILINGS TODAY WILL REMAIN VFR IN MOST PLACES, WITH WIDESPREAD DROPS
DOWN TO MVFR EXPECTED GOING INTO SUNDAY MORNING WITH A STRONG
ONSHORE PUSH. COUPLE BREEZY WINDS TO 20 KT ARE POSSIBLE ALONG THE
PACIFIC COAST/STRAIT OF JUAN DE FUCA AREAS LATER TODAY. OTHERWISE
EXPECT WEST/NORTHWEST WINDS 5 TO 10 KT THIS AFTERNOON, WITH WIND
SHIFTING TO THE SOUTHWEST EXPECTED LATER TONIGHT/SUNDAY BEHIND THE
FRONT.
KSEA...COLD FRONT IS BRINGING SHOWERS THROUGH EARLY THIS MORNING.
SOME GUIDANCE IS HINTING AT A LINGERING CONVERGENCE ZONE CONTINUING
SHOWER ACTIVITY UP TO 18Z. THIS WILL LIKELY DROP CEILINGS DOWN TO
MVFR FROM ROUGHLY 12Z TO 18Z BEFORE IMPROVING TO VFR. WINDS MAY GET
A LITTLE SQUARELY WITH THE CONVERGENCE ZONE, BUT DIRECTION IS
EXPECTED TO BE OUT OF THE NORTH TODAY ARE AROUND 5 TO 10 KT. A SHIFT
TO THE SOUTH IS EXPECTED AROUND 05Z LATE SATURDAY EVENING. LOWER
CEILINGS DOWN TO MVFR ARE LIKELY SUNDAY MORNING.
HPR
MARINE
A QUICK MOVING COLD FRONT WILL SWEEP A LINE OF SHOWERS
OVER THE WATERS EARLY THIS MORNING. THE TROUGH WILL ELONGATE A BIT
GOING INTO SUNDAY BEFORE BUILDING HIGH PRESSURE TAKES OVER THE
TROUGH GOING INTO MONDAY. GUSTY WINDS WILL CONTINUE THIS WEEKEND,
PROMPTING ANOTHER ROUND OF SMALL CRAFT ADVISORIES FOR THE ENTIRE
STRAIT OF JUAN DE FUCA AND ADMIRALTY INLET (ESPECIALLY AS HIGH
PRESSURE BUILDS IN POST-FRONT). ANOTHER PUSH IS EXPECTED SUNDAY
NIGHT INTO MONDAY WITH BREEZY WINDS THROUGH THE STRAIT OF JUAN DE
FUCA.
COASTAL WATERS: BESIDES THE WIND DECREASING TODAY, SEAS WILL
CONTINUE TO REMAIN HAZARDOUS FOR THE SMALL CRAFT (PRIMARILY DUE TO
SEAS OF 8 TO 10 FT AT 8 SECONDS CONTINUING THROUGH PARTWAY INTO
SUNDAY). ADDITIONAL BREEZY WINDS ARE POSSIBLE IN THE NORTHERN MARINE
ZONES SUNDAY INTO MONDAY WITH THE NEXT SYSTEM. A DROP IN SEAS DOWN
TO 5 TO 7 FEET IS EXPECTED ON TUESDAY.
HPR
HYDROLOGY
NO RIVER FLOODING IS EXPECTED THROUGH THE NEXT 7
DAYS.
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...SMALL CRAFT ADVISORY FROM 2 PM THIS AFTERNOON TO 2 AM PDT SUNDAY
FOR ADMIRALTY INLET-CENTRAL U.S. WATERS STRAIT OF JUAN DE
FUCA-EAST ENTRANCE U.S. WATERS STRAIT OF JUAN DE FUCA-WEST
ENTRANCE U.S. WATERS STRAIT OF JUAN DE FUCA.
SMALL CRAFT ADVISORY UNTIL 2 AM PDT EARLY THIS MORNING FOR
ADMIRALTY INLET-EAST ENTRANCE U.S. WATERS STRAIT OF JUAN DE
FUCA.
SMALL CRAFT ADVISORY UNTIL 8 AM PDT THIS MORNING FOR NORTHERN
INLAND WATERS INCLUDING THE SAN JUAN ISLANDS.
SMALL CRAFT ADVISORY UNTIL 5 AM PDT SUNDAY FOR COASTAL WATERS
FROM CAPE FLATTERY TO JAMES ISLAND 10 TO 60 NM-COASTAL
WATERS FROM CAPE FLATTERY TO JAMES ISLAND OUT 10 NM-COASTAL
WATERS FROM JAMES ISLAND TO POINT GRENVILLE 10 TO 60 NM-
COASTAL WATERS FROM JAMES ISLAND TO POINT GRENVILLE OUT 10
NM-COASTAL WATERS FROM POINT GRENVILLE TO CAPE SHOALWATER
10 TO 60 NM-COASTAL WATERS FROM POINT GRENVILLE TO CAPE
SHOALWATER OUT 10 NM.
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