561
FXUS66 KSEW 060416
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
816 PM PST FRI DEC 5 2025
UPDATE
CONVERGENCE ZONE ACTIVITY REMAINS OVER SNOHOMISH COUNTY THIS
EVENING WITH SCATTERED SHOWERS ELSEWHERE. ISOLATED WIND GUSTS
UPWARDS OF 40-45 MPH HAVE BEEN OBSERVED WITHIN THE LAST FEW
HOURS, RESULTING IN A SHORT-FUSED WIND ADVISORY BEING ISSUED
FOR THE SEATTLE/TACOMA METRO FOR TONIGHT. RAIN SHOWERS ARE
FAVORED TO REMAIN OVERNIGHT WITH SNOWFALL EXPECTED FOR
ELEVATIONS NEAR 4,000 FT AND ABOVE.
SYNOPSIS
THE WEATHER PATTERN HAS TRANSITIONED INTO AN ACTIVE PHASE AS A
SERIES OF SYSTEM BRING RAIN, HIGH ELEVATION SNOW AND WIND INTO
THE REGION THROUGH THE END OF THE WEEKEND. A STRONG ATMOSPHERIC
RIVER IS STILL ON TRACK TO REGION THE AREA BY MONDAY AND LAST
INTO AT LEAST THE MIDWEEK TIME FRAME. THIS SYSTEM WILL BRING
VERY SIGNIFICANT RAINFALL AND LIKELY HYDROLOGIC IMPACTS. COASTAL
FLOODING DUE TO HIGHER ASTRONOMICAL TIDES WILL REMAIN MINOR INTO
EARLY NEXT WEEK.
DISCUSSION
KEY MESSAGES...
* RAIN: A FEW RELATIVELY MINOR SYSTEMS WILL SWEEP ACROSS THE
AREA TONIGHT, AND ON SUNDAY, BEFORE A STRONG ATMOSPHERIC RIVER
SYSTEM WILL BRING HEAVY PRECIPITATION THE AREA MONDAY THROUGH
AT LEAST WEDNESDAY. MODELS ENSEMBLES ARE BEGINNING TO SHOW
ANOTHER ROUND OF HEAVY PRECIPITATION THURSDAY INTO FRIDAY AS
WELL, NOW. THE HYDROLOGIC IMPLICATIONS WILL BE DETAILED IN THE
HYDROLOGY SECTION.
* SNOW: LOWERING SNOW LEVELS TONIGHT TO JUST BELOW 4000 FT WILL
ALLOW FOR SIGNIFICANT ACCUMULATING SNOW FOR STEVENS PASS AND
WHITE PASS. HEAVY PRECIPITATION THROUGH TONIGHT INTO EARLY
SATURDAY, AS WELL AS THE POTENTIAL FOR A CONVERGENCE ZONE LATE
TONIGHT WILL ALLOW FOR 1-1.5"/HR+ SNOWFALL RATES, WHICH WILL
MAKE TRAVEL VERY DIFFICULT. WIND GUSTS UP TO 30-35 MPH WILL
LIMIT VISIBILITY AT TIMES AS WELL. CHECK WSDOT FOR THE LATEST
PASS CONDITIONS AND FOR CLOSURES.
* WIND: WINDS WILL GENERALLY BE ELEVATED THROUGH THE NEXT 7
DAYS, BUT THE TIME PERIODS FOR THE STRONGEST WINDS WILL BE
TONIGHT, AS WELL AS ON MONDAY, WHERE GUSTS UP TO 45 MPH WILL
BE POSSIBLE ALONG THE PACIFIC COAST, THE STRAIT/NORTHWEST
INTERIOR, AS WELL AS THROUGH THE CASCADE MOUNTAINS.
* COASTAL FLOODING: TIDES HAVE NOW PEAKED FOR THE PACIFIC
COAST, THROUGH WITH LARGER WAVES COMING IN TOMORROW, THE
POTENTIAL FOR MINOR COASTAL FLOODING IMPACTS WILL BE POSSIBLE
AGAIN ON SATURDAY, MAINLY FOR THE BEACHES OF GRAYS HARBOR
COUNTY. FOR THE NORTHERN INTERIOR WATERS, TIDE LEVELS THIS
WEEKEND WILL RISE, ALLOWING FOR MOSTLY MINOR COASTAL FLOODING
IMPACTS. GOING INTO NEXT WEEK, ACTIVE WEATHER LOOKS TO KEEP
TIDE LEVELS HIGH AND MAY CREATE ADDITIONAL IMPACTS FOR PUGET
SOUND COASTLINES AS WELL.
AS OF THIS AFTERNOON, RADAR IMAGERY IS SHOWING THE STRONG INFLUX
OF MOISTURE, CREATING SHOWERS ACROSS THE PACIFIC COAST AND
THROUGH THE CASCADE MOUNTAINS. AS THE SUPPORTING SHORTWAVE
TROUGH ALOFT BEGINS TO MOVE ACROSS THE AREA, THAT WILL BEGIN TO
PUSH IN EVEN MORE MOISTURE, AS WELL AS INCREASE WESTERLY WINDS
ACROSS THE AREA. MOST LOCATIONS WILL SEE WINDS GUSTS BETWEEN
25-35 MPH, BUT ISLAND COUNTY MAY SEE GUSTS UP TO 45 MPH, WHICH
WARRANTS THE WIND ADVISORY THROUGH TONIGHT. THIS WILL ALSO
BRING SOME COOLER AIR, WHICH WILL ALLOW FOR SNOW LEVELS TO DROP
BELOW 4000 FT, WHERE IMPACTS WILL START TO BE FELT AT STEVENS
AND WHITE PASSES. WITH THE INCREASED WESTERLY WINDS, WE WILL
LIKELY SEE THE DEVELOPMENT OF A CONVERGENCE ZONE ACROSS
CENTRAL/SOUTHERN SNOHOMISH COUNTY, WHICH WILL BE FLIRTING
CLOSELY WITH STEVENS PASS. REGARDLESS, MOISTURE WILL CONTINUE TO
FILTER IN ACROSS THE AREA THROUGH TONIGHT INTO SATURDAY,
PRIMARILY FOCUSED ON THE CASCADES. LATEST HI-RES GUIDANCE IS
SHOWING THE POTENTIAL FOR 1-1.5"/HR+ SNOWFALL RATES OVER THE
PASSES TONIGHT, AND AS SUCH, TOTAL ACCUMULATIONS THROUGH
TOMORROW AFTERNOON WILL LIKELY SURPASS A FOOT AT STEVENS PASS,
PERHAPS AS MUCH AS 16-18 INCHES. LOCALLY HIGHER AMOUNTS ARE
EXPECTED AT THE HIGHER PEAKS, AND AT LOCATIONS SUCH AS PARADISE
AND MT. BAKER SKI AREA. AS SUCH, A WINTER STORM WARNING IS IN
EFFECT FOR STEVENS PASS, WHILE SLIGHTLY LOWER AMOUNTS ARE
FORECAST FOR WHITE PASS, LENDING TO A WINTER WEATHER ADVISORY.
THESE PRODUCTS ARE IN EFFECT THROUGH SATURDAY EVENING.
THERE WILL LIKELY BE A BRIEF LULL IN THE PRECIPITATION
OVERNIGHT ON SATURDAY, BUT IT WON'T BE LONG UNTIL THE NEXT
SYSTEM ARRIVES SUNDAY MORNING. PRECIPITATION AMOUNTS WITH THIS
SYSTEMS WILL BE RELATIVELY LIGHT--A QUARTER TO A HALF INCH
ACROSS THE LOWLANDS, WITH UP TO AN INCH OR TWO FOR THE COAST AND
MOUNTAINS. RISING SNOW LEVELS BACK UP TO AROUND 4500-5000 FT
WILL ALLOW FOR RAIN AT THE PASSES. NO MAJOR HYDROLOGIC IMPACTS
ARE EXPECTED WITH THIS SYSTEM, BUT IT WILL PRIME THE SOIL AND
THE RIVERS FOR WHAT WILL COME NEXT WEEK.
A STRONG 100-125 KT JET (AT 500 MB) WILL BECOME AIMED AT WESTERN
WASHINGTON STARTING ON MONDAY AND CONTINUING THROUGH WEDNESDAY.
ACCOMPANYING THAT WILL BE A PLUME OF SIGNIFICANT MOISTURE;
PRECIPITABLE WATER VALUES WILL REACH UP TO 1-1.5", WHICH IS
250-300%+ ABOVE NORMAL FOR THIS TIME OF YEAR. MODELS ARE SHOWING
INTEGRATED VAPOR TRANSPORT VALUES REACHING OR EXCEEDING 750-1000
J/KG DURING THIS TIME PERIOD. NEEDLESS TO SAY, A LOT OF WATER
WILL ACCOMPANY THIS ATMOSPHERIC RIVER HEADED THIS WAY. HEAVY
RAIN WILL BEGIN TO ARRIVE EARLY ON MONDAY AND CONTINUE THROUGH
EARLY TUESDAY. THE MAIN MOISTURE PLUME LOOKS TO BRIEFLY SINK
SOUTHWARD ON TUESDAY, ALLOWING FOR A BRIEF LULL IN THE HEAVY
RAIN BEFORE ANOTHER PUNCH OF MOISTURE BRINGS BACK THE HEAVY RAIN
ON WEDNESDAY. IN THIS PERIOD, THE LATEST RAINFALL TOTALS PUT
AROUND 3 TO 5 INCHES ACROSS THE INTERIOR LOWLANDS, 4 TO 6 INCHES
ALONG THE COAST, AND 8 TO LOCALLY 12+ INCHES ACROSS THE
MOUNTAINS. FLOODING IS LIKELY; NOT JUST THE RIVERS, BUT ALSO
URBAN/SMALL STREAM FLOODING AS WELL. MORE DETAILS ON THE
HYDROLOGIC IMPACTS ARE BELOW IN HYDROLOGY. WHILE THE FORECAST
TREND IN QPF CONTINUES TO INCH UPWARD, THINGS CAN CHANGE, SO IT
IS PERTINENT TO STAY TUNED TO THE LATEST UPDATES.
LASTLY, MODELS ARE STARTING TO SHOW INDICATIONS OF ANOTHER
WEATHER SYSTEM BRINGING SIGNIFICANT PRECIPITATION LATE THURSDAY
INTO FRIDAY. WHILE IT MAY NOT BE AS MUCH AS WE'LL SEE FROM
MONDAY-WEDENSDAY, WITH SATURATED SOILS AND RIVERS ALREADY
RUNNING VERY HIGH, THIS RAIN MAY PROLONG OR EXACERBATE THE
HYDROLOGIC IMPACTS EXPECTED BY MID-WEEK.
AS TYPICAL IN A RAINY/ATMOSPHERIC RIVER SETUP, TEMPERATURES
THROUGH THE WEEK WILL REMAIN SLIGHTLY ABOVE NORMAL, WITH HIGHS
GENERALLY IN THE LOW TO MID 50S AND LOWS IN THE 40S.
62
AVIATION
NORTHWEST FLOW ALOFT WILL CONTINUE TONIGHT AS A FRONTAL SYSTEM
PUSHES INLAND ACROSS WESTERN WASHINGTON. CONDITIONS ARE PRIMARILY
A MIX OF IFR TO MVFR ACROSS THE MAJORITY OF THE AREA TERMINALS THIS
EVENING WITH A CONVERGENCE ZONE CONTINUING OVER SNOHOMISH COUNTY,
WHICH WILL BRING ADDITIONAL POST- FRONTAL SHOWERS AND GUSTY WINDS
ACROSS THE REGION TONIGHT (MAINLY IMPACTING KPAE). FORECAST MODELS
ALSO SHOW AREAS OF LOW LEVEL WIND SHEAR EAST OF THE OLYMPIC
MOUNTAINS AND OVER THE CASCADES, BUT IS NOT EXPECTED TO IMPACT THE
WESTERN WASHINGTON TERMINALS. LOCALIZED BRIEF IMPROVEMENTS TO VFR
WILL STILL BE POSSIBLE THIS EVENING IN THE POST-FRONTAL AIRMASS,
HOWEVER EXPECT MORE WIDESPREAD MVFR CONDITIONS FOR MOST TERMINALS
INTO SATURDAY MORNING. SHOWER ACTIVITY WILL INCREASE AGAIN OVERNIGHT
INTO SATURDAY MORNING. S/SW SURFACE WINDS WILL PEAK TONIGHT, BUT
REMAIN BREEZY INTO SATURDAY, WITH GUSTS GENERALLY RANGING BETWEEN 20
TO 30 KTS FOR MOST AREAS, THOUGH LOCALIZED GUSTS TO 35 KTS WILL BE
POSSIBLE IN SOME SPOTS AS WELL.
KSEA...MVFR CIGS THIS EVENING, LIKELY PERSISTING INTO SATURDAY
OUTSIDE OF ANY DRIZZLE/SHOWER ACTIVITY. A CONVERGENCE ZONE WILL
CONTINUE OVER THE NORTHERN PUGET SOUND, BUT WILL REMAIN WELL NORTH
OF THE TERMINAL. S/SW WINDS PERSISTING AT 10-20 KTS WILL PEAK
TONIGHT, WITH GUSTS BETWEEN 25-35 KTS POSSIBLE AT TIMES. WINDS WILL
EASE SOMEWHAT INTO SATURDAY, BUT WILL REMAIN BREEZY WITH GUSTS TO 25
KTS AT TIMES THROUGH THE DAY.
MARINE
A WEATHER SYSTEM MOVING INLAND TONIGHT WILL CONTINUE TO BRING
GUSTY WINDS TO THE AREA WATERS INTO SATURDAY MORNING. WESTERLY
GALE FORCE WIND GUSTS WILL REMAIN POSSIBLE INTO EARLY SATURDAY
FOR THE COASTAL WATERS AND WESTERN STRAIT OF JUAN DE FUCA IN ITS
WAKE. A STRONG PUSH OF WESTERLY WINDS IS ALSO LIKELY ALONG THE
STRAIT OF JUAN DE FUCA TONIGHT, WHERE LOCALIZED GUSTS TO 45 KTS
WILL BE POSSIBLE AT TIMES.
STRONGER SOUTHWESTERLY WINDS ARE ALSO EXPECTED ALONG THE SOUTHERN
PORTIONS OF THE NORTHERN INLAND WATERS AND NEAR BELLINGHAM BAY
TONIGHT, WHERE GUSTS TO 35 KTS REMAIN POSSIBLE. GUSTS MAY ALSO
PEAK BRIEFLY AROUND 35 KTS FOR PUGET SOUND AS WELL TONIGHT,
THOUGH EXPECT PREDOMINANTLY SCA WINDS TO PREVAIL FOR THE
MAJORITY OF THE AREA. WINDS WILL SLOWLY SUBSIDE AREA-WIDE ON
SATURDAY. ADDITIONAL WEATHER SYSTEMS ARE EXPECTED OVER THE NEXT
WEEK - THE NEXT BEING ON SUNDAY MORNING, WITH A STRONGER
SYSTEM FOLLOWING ON MONDAY AND TUESDAY. FURTHER HEADLINES WILL
LIKELY BE REQUIRED, WITH POTENTIAL GALES AGAIN WITH THE MONDAY/
TUESDAY WEATHER SYSTEM.
SEAS WILL BUILD TO 13 TO 18 FEET TONIGHT INTO SATURDAY MORNING,
BEFORE SUBSIDING BACK TOWARDS 8 TO 10 FEET BY LATE SATURDAY
NIGHT. SEAS WILL BUILD AGAIN STARTING LATE MONDAY AS THE NEXT
ROUND OF WEATHER SYSTEMS MOVE INTO THE REGION.
HYDROLOGY
A SERIES OF WET WEATHER SYSTEMS MOVING ACROSS THE REGION WILL
INCREASE THE THREAT OF RIVER FLOODING EARLY NEXT WEEK. WHILE THERE'S
STILL SOME UNCERTAINTY IN THE POSSIBLE PRECIPITATION AMOUNTS WITH AN
ATMOSPHERIC RIVER MOVING INTO THE REGION THE FIRST PART OF NEXT
WEEK, CONFIDENCE CONTINUES TO INCREASE IN HEAVY RAINFALL OCCURING
ACROSS WESTERN WA, ESPECIALLY OVER THE OLYMPICS AND CASCADES.
CONFIDENCE ALSO CONTINUES TO INCREASE THAT A WIDESPREAD RIVER
FLOODING EVENT WILL COMMENCE LATE MONDAY, THROUGHOUT TUESDAY AND
INTO WEDNESDAY, WITH MULTIPLE RIVERS FLOWING OFF THE CASCADES AND
THE OLYMPICS REACHING MINOR, MODERATE, AND MAJOR FLOOD STAGE.
ADDITIONAL PRECIPITATION IS ALSO POSSIBLE THURSDAY INTO FRIDAY,
WHICH WILL KEEP RIVERS ELEVATED THROUGH THE SECOND HALF OF THE WEEK.
UNCERTAINTY DOES REMAIN IN REGARDS TO THE EXACT FLOOD LEVELS AND
STAGES THROUGH NEXT WEEK, AND AS SUCH, IT WILL BE CRITICAL TO
MONITOR THE FORECASTS THROUGH THE NEXT SEVEN DAYS.
THE SERIES OF WET SYSTEMS WILL ALSO START TO ELEVATE THE LANDSLIDE
RISK ACROSS THE REGION THROUGHOUT THE WEEKEND, WITH CONDITIONS
EXPECTED INCREASE RAPIDLY EARLY NEXT WEEK WITH THE ARRIVAL OF AN
ATMOSPHERIC RIVER.
URBAN AND SMALL STREAM FLOODING, AS WELL AS AREAS WITH POOR
DRAINAGE, SHOULD BE ALERT TO THE POTENTIAL FOR LOCALIZED NUISANCE
FLOODING. LOW WATER CROSSINGS MAY BECOME IMPACTED OR IMPASSABLE.
14/62
SEW WATCHES/WARNINGS/ADVISORIES
WA...COASTAL FLOOD ADVISORY FROM 4 AM TO 10 AM PST SATURDAY FOR
LOWLANDS OF WESTERN SKAGIT AND NORTHWESTERN SNOHOMISH
COUNTIES-LOWLANDS OF WESTERN WHATCOM COUNTY-SAN JUAN
COUNTY.
COASTAL FLOOD ADVISORY FROM 5 AM TO 11 AM PST SUNDAY FOR
LOWLANDS OF WESTERN SKAGIT AND NORTHWESTERN SNOHOMISH
COUNTIES-LOWLANDS OF WESTERN WHATCOM COUNTY-SAN JUAN
COUNTY.
FLOOD WATCH FROM LATE SUNDAY NIGHT THROUGH FRIDAY AFTERNOON
FOR CASCADES OF PIERCE AND LEWIS COUNTIES-CASCADES OF
SNOHOMISH AND NORTHERN KING COUNTIES-CASCADES OF SOUTHERN
KING COUNTY-CASCADES OF WHATCOM AND SKAGIT COUNTIES-CITY
OF SEATTLE-DOWNTOWN EVERETT / MARYSVILLE AREA-EASTERN
KITSAP COUNTY-EASTERN STRAIT OF JUAN DE FUCA-EASTSIDE-
FOOTHILLS AND VALLEYS OF CENTRAL KING COUNTY-FOOTHILLS
AND VALLEYS OF PIERCE AND SOUTHERN KING COUNTIES-
FOOTHILLS AND VALLEYS OF SNOHOMISH AND NORTHERN KING
COUNTIES-FOOTHILLS AND VALLEYS OF THURSTON AND LEWIS
COUNTIES-FOOTHILLS AND VALLEYS OF THE NORTH CASCADES-
FOOTHILLS OF THE WESTERN AND SOUTHERN OLYMPIC PENINSULA-
GRAYS HARBOR COUNTY COAST-ISLAND COUNTY-LAKE CRESCENT
AREA INCLUDING US 101-LOWER CHEHALIS RIVER VALLEY-
LOWLANDS OF LEWIS AND SOUTHERN THURSTON COUNTIES-LOWLANDS
OF PIERCE AND SOUTHERN KING COUNTIES-LOWLANDS OF WESTERN
SKAGIT AND NORTHWESTERN SNOHOMISH COUNTIES-LOWLANDS OF
WESTERN WHATCOM COUNTY-MIDDLE CHEHALIS RIVER VALLEY-
NORTHERN HOOD CANAL-NORTHERN WASHINGTON COAST-OLYMPIA AND
SOUTHERN PUGET SOUND-OLYMPICS-PORT TOWNSEND AREA-SAN JUAN
COUNTY-SHORELINE / LYNNWOOD / SOUTH EVERETT AREA-SOUTHERN
HOOD CANAL-WESTERN STRAIT OF JUAN DE FUCA-WILLAPA AND
BLACK HILLS.
WINTER STORM WARNING UNTIL 10 PM PST SATURDAY FOR CASCADES OF
SNOHOMISH AND NORTHERN KING COUNTIES.
WINTER WEATHER ADVISORY UNTIL 7 PM PST SATURDAY FOR CASCADES
OF PIERCE AND LEWIS COUNTIES.
WIND ADVISORY UNTIL MIDNIGHT PST TONIGHT FOR CITY OF SEATTLE-
LOWLANDS OF PIERCE AND SOUTHERN KING COUNTIES.
COASTAL FLOOD ADVISORY FROM 9 AM TO 3 PM PST SATURDAY FOR
GRAYS HARBOR COUNTY COAST.
WIND ADVISORY UNTIL 7 AM PST SATURDAY FOR ISLAND COUNTY.
PZ...SMALL CRAFT ADVISORY UNTIL 10 PM PST SATURDAY FOR GRAYS HARBOR
BAR.
GALE WARNING UNTIL 4 AM PST SATURDAY 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-WEST ENTRANCE U.S.
WATERS STRAIT OF JUAN DE FUCA.
SMALL CRAFT ADVISORY FROM 4 AM TO 10 PM PST SATURDAY 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-WEST
ENTRANCE U.S. WATERS STRAIT OF JUAN DE FUCA.
GALE WARNING UNTIL 10 AM PST SATURDAY FOR CENTRAL U.S. WATERS
STRAIT OF JUAN DE FUCA-EAST ENTRANCE U.S. WATERS STRAIT
OF JUAN DE FUCA-NORTHERN INLAND WATERS INCLUDING THE SAN
JUAN ISLANDS.
SMALL CRAFT ADVISORY UNTIL 4 AM PST SATURDAY FOR ADMIRALTY
INLET-PUGET SOUND AND HOOD CANAL.
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