912
FXUS66 KSEW 180247
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
747 PM PDT TUE MAR 17 2026
SYNOPSIS
AN ATMOSPHERIC RIVER WILL REMAIN STATIONED OVER WESTERN
WASHINGTON THROUGH THE WEEK, MAINTAINING WARM AND WET CONDITIONS.
WITH SNOW LEVELS AROUND 8000 FEET, RIVER FLOODING DUE TO HEAVY
RAIN AND SNOWMELT REMAINS POSSIBLE FOR MUCH OF THE CASCADES.
CONDITIONS WILL COOL DOWN AND DRY OUT BRIEFLY OVER THE WEEKEND
BEFORE ADDITIONAL SYSTEMS BRING IN ACTIVE WEATHER NEXT WEEK.
SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/
AN ATMOSPHERIC RIVER WILL CONTINUE TO PULL IN WARM, MOIST AIR
FROM THE DEEP PACIFIC, RESULTING IN STEADY RAINFALL ACROSS
WESTERN WASHINGTON OVER THE NEXT SEVERAL DAYS. THE WARMER AIR
HAS ALLOWED SNOW LEVELS TO RISE AS HIGH AS 8000 FEET, WITH
NEARLY ALL PRECIPITATION OVER THE MOUNTAINS FALLING AS RAIN. THE
HEAVIEST RAIN WILL BE FOCUSED OVER THE OLYMPIC PENINSULA AND
CASCADES, WHERE UPWARDS OF 6 TO 10 INCHES OF RAINFALL ARE
POSSIBLE BETWEEN TODAY AND FRIDAY. THE RAIN-ON-SNOW AND SNOW
MELT WILL CONTRIBUTE TO SIGNIFICANT RUNOFF IN ADDITION TO THE
INCOMING RAINFALL, INCREASING THE RISK OF RIVER FLOODING OVER
THE MOUNTAINS. THE LOWLANDS ARE ALSO ON TRACK TO SEE 1 TO 2
INCHES OF RAIN THROUGH FRIDAY, WHICH MAY RESULT IN ROADWAY
PONDING AND LOCALIZED NUISANCE FLOODING. THE RISK FOR LANDSLIDES
WILL ALSO INCREASE TOWARDS THE END OF THE WEEK AS A RESULT OF
THE INCOMING RAINFALL AND SNOW MELT. FOR MORE INFORMATION ON
RIVER FLOODING, SEE THE HYDROLOGY SECTION BELOW.
IN ADDITION TO WET CONDITIONS, WESTERN WASHINGTON WILL SEE MILD
TEMPERATURES FOR THE REST OF THE WORK WEEK WITH HIGHS IN THE MID
TO UPPER 50S ACROSS THE LOWLANDS. OVERNIGHT LOW TEMPERATURES
WILL ALSO REMAIN ELEVATED, WITH LOWS BOTTOMING OUT AROUND 50
DEGREES FOR MUCH OF THE LOWLANDS. SOUTHERLY WINDS WILL ALSO
REMAIN BREEZY AT TIMES THROUGH FRIDAY, WITH GUSTS RANGING
BETWEEN 20 TO 35 MPH. THE STRONGEST WINDS WILL OCCUR ALONG THE
PACIFIC COAST AND FROM EVERETT NORTHWARDS ACROSS THE INTERIOR.
LONG TERM /FRIDAY THROUGH TUESDAY/
BY FRIDAY NIGHT, A
TRAILING COLD FRONT BEHIND THE ATMOSPHERIC RIVER SYSTEM WILL
PUSH THE BULK OF THE REMAINING PRECIPITATION SOUTHWARD TOWARDS
SOUTHERN OREGON. TEMPERATURES ACROSS WESTERN WASHINGTON WILL
COOL OFF SEVERAL DEGREES, WITH SNOW LEVELS LOWERING TO
1500-2500 FEET. LIGHT SNOW WILL LINGER OVER THE MOUNTAINS INTO
SATURDAY AND SUNDAY AS THE LOWLANDS BRIEFLY DRY OUT UNDER
CLOUDY SKIES. MODELS REMAIN IN GOOD AGREEMENT OVER ANOTHER WET
WEATHER SYSTEM MOVING INTO THE REGION BY THE START OF NEXT WEEK,
THOUGH THE DETAILS REMAIN FAIRLY UNCERTAIN.
15
AVIATION
STRONG WESTERLY FLOW ALOFT WILL CONTINUE TONIGHT ACROSS WESTERN
WASHINGTON AS A MOIST AIR MASS CONTINUES TO FUNNEL RAIN INTO THE
REGION AHEAD OF A STALLED FRONTAL BOUNDARY OVER BRITISH COLUMBIA.
MOST TERMINALS ARE REPORTING VFR CONDITIONS AT THE TIME OF THIS
WRITING WITH ONLY HQM, PWT AND PAE CURRENTLY REPORTING MVFR/IFR
CONDITIONS. IT IS WORTH NOTING THAT TERMINALS CURRENTLY REPORTING
VFR DO HAVE FEW-SCT CLOUDS AT MVFR/IFR LEVELS AND HAVE BOUNCED BACK
AND FORTH FROM VFR TO MVFR AT TIMES THIS AFTERNOON. AS PRECIP
PERSISTS, ADDING MORE LOW-LEVEL MOISTURE TO THE AREA, WIDESPREAD
MVFR TO IFR CONDITIONS ARE EXPECTED TO EMERGE BETWEEN 03-06Z THIS
EVENING AND PERSIST FOR THE REMAINDER OF THE TAF PERIOD. PERSISTENT
PRECIP WILL ALSO IMPACT VISIBILITY THROUGHOUT THE CWA, INTRODUCING
LIMITATIONS FROM TIME TO TIME. SOUTHERLY WINDS GENERALLY 5-10 KT.
BREEZY CONDITIONS EXPECTED FROM PAE NORTHWARDS WITH SUSTAINED SPEEDS
10-15 KT AND GUSTS 20-25 KT.
KSEA...CURRENTLY REPORTING VFR CIGS, HOWEVER GIVEN THE PATTERN OF
RISING AND LOWERING CIGS EARLIER THIS AFTERNOON, DIFFICULT TO PUT
TOO MUCH STOCK IN HOW LONG THESE HIGHER CIGS WILL CONTINUE. MVFR
CONDITIONS EXPECTED TO EMERGE BY 06Z AND IF CURRENT RADAR TRENDS
HOLD UP, WITH LIGHTER ECHOES EXPECTED OVER THE TERMINAL IN THE NEAR
TERM, THIS TIMING MAY BE ON TRACK. IN AGREEMENT WITH INHERITED
FORECAST THAT THE THREAT FOR IFR CONDITIONS, WHILE NOT GONE
ENTIRELY, SEEMS LOW WITH LOW-END MVFR CONTINUING TO BE FAVORED AS
PRECIP PICKS UP OVERNIGHT. WILL CONTINUE TO MONITOR MODEL OUTPUT
BEFORE MAKING DECISION FOR 06Z TAFS. S/SW WINDS 5-7 KT THIS EVENING
AND OVERNIGHT BEFORE INCREASING TO 8-10 KT WEDNESDAY MORNING.
29/18
MARINE
SOUTHERLY FLOW WILL CONTINUE ACROSS THE WATERS INTO WEDNESDAY AS A
FRONTAL BOUNDARY REMAINS STALLED IN BRITISH COLUMBIA. AS A RESULT,
SMALL CRAFT WINDS AND GUSTS WILL CONTINUE ACROSS INTERIOR WATERS
TODAY AND INTO WEDNESDAY MORNING. IN ADDITION, A SMALL CRAFT
ADVISORY CONTINUES ACROSS THE COASTAL WATERS FOR SEAS. SEAS WILL
CONTINUE TO EASE TONIGHT AND EXPECTED TO BE BELOW 10 FT BY WEDNESDAY
MORNING. SMALL CRAFT WINDS ARE LIKELY ACROSS THE COASTAL WATERS
WEDNESDAY NIGHT INTO THURSDAY, WITH CURRENT PROBABILITIES GREATER
THAN 80%. A COLD FRONT WILL MOVE OVER AREA WATERS ON FRIDAY THROUGH
SATURDAY. AS THE FRONT PASSES THROUGH THE STRAIT OF JUAN DE FUCA ,
THERE IS THE POTENTIAL (45-70% CHANCE) FOR SMALL CRAFT WINDS FOR THE
WESTERN AND CENTRAL STRAIT.
29/18
HYDROLOGY
AN ATMOSPHERIC RIVER WILL CONTINUE TO BRING STEADY RAINFALL TO
WESTERN WASHINGTON THROUGH FRIDAY. SNOW LEVELS WILL REMAIN
AROUND 7000-8000 FEET, FALLING AS MOSTLY RAIN OVER HIGHER
TERRAIN. RAINFALL TOTALS OVER THE OLYMPIC PENINSULA AND CASCADES
HAS SLIGHTLY INCREASED, WITH A TOTAL OF 6 TO 10 INCHES OVER THE
OLYMPIC MOUNTAINS AND CENTRAL AND NORTHERN CASCADES THROUGH
FRIDAY. ELSEWHERE, RAINFALL TOTALS AROUND 1 TO 3 INCHES CAN BE
EXPECTED.
THE COMBINATION OF STEADY RAIN, ELEVATED SNOW LEVELS, AND LOW
LEVEL SNOW MELT WILL PUT PRESSURE ON AREA RIVERS INTO THE
WEEKEND. RIVERS IN THE CASCADES FROM KING COUNTY NORTHWARD HAVE
THE HIGHEST CHANCE OF REACHING FLOOD STAGE, WITH THE SNOQUALMIE,
SNOHOMISH, AND TOLT RIVER FORECASTS ALL CREEPING CLOSE TO MAJOR
FLOOD STAGE BETWEEN LATE WEDNESDAY AND THURSDAY. THE SKAGIT
RIVER IS ALSO NOW FORECAST TO FLOOD BY THURSDAY AND RISE TO NEAR
MAJOR FLOOD STAGE BY FRIDAY. IN ADDITION, THE FLOOD- PRONE
SKOKOMISH RIVER IN MASON COUNTY IS FORECAST TO ENTER MINOR FLOOD
STAGE ON WEDNESDAY AND CREST ONCE AGAIN IN MINOR FLOOD STAGE ON
FRIDAY. FLOOD WATCHES REMAIN IN EFFECT FOR MASON COUNTY AND FOR
KING COUNTY NORTHWARD, WHERE FLOODING IS MOST LIKELY TO OCCUR
ON AREA RIVERS LATE WEDNESDAY INTO THURSDAY, WITH IMPACTS
POSSIBLE INTO THE WEEKEND.
THE SNOW MELT FACTOR IS COMPLICATING RIVER FORECASTS, AS THE
MELTING SNOW OFF OF THE MOUNTAINS COULD CONTRIBUTE AN ADDITIONAL
10 TO 15 PERCENT OF THE TOTAL WATER IN THE SYSTEM. THIS ADDED
VARIABLE COULD ENHANCE THE POTENTIAL FLOODING LATER IN THE WEEK.
15
SEW WATCHES/WARNINGS/ADVISORIES
WA...FLOOD WATCH FROM WEDNESDAY AFTERNOON THROUGH FRIDAY AFTERNOON
FOR 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-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 THE NORTH
CASCADES-LOWLANDS OF PIERCE AND SOUTHERN KING COUNTIES-
LOWLANDS OF WESTERN SKAGIT AND NORTHWESTERN SNOHOMISH
COUNTIES-LOWLANDS OF WESTERN WHATCOM COUNTY-SHORELINE /
LYNNWOOD / SOUTH EVERETT AREA.
FLOOD WATCH THROUGH FRIDAY AFTERNOON FOR FOOTHILLS OF THE
WESTERN AND SOUTHERN OLYMPIC PENINSULA-MIDDLE CHEHALIS
RIVER VALLEY-OLYMPIA AND SOUTHERN PUGET SOUND-OLYMPICS-
SOUTHERN HOOD CANAL-WILLAPA AND BLACK HILLS.
PZ...SMALL CRAFT ADVISORY UNTIL 5 AM PDT WEDNESDAY FOR ADMIRALTY
INLET-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-
NORTHERN INLAND WATERS INCLUDING THE SAN JUAN ISLANDS-
PUGET SOUND AND HOOD CANAL-WEST ENTRANCE U.S. WATERS
STRAIT OF JUAN DE FUCA.
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