294
FXUS66 KSEW 181021
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
321 AM PDT WED MAR 18 2026
SYNOPSIS
ATMOSPHERIC RIVER WILL REMAIN OVER WESTERN WASHINGTON THROUGH
FRIDAY. THE RIVER WILL MOVE OUT FRIDAY NIGHT. ZONAL FLOW ALOFT
OVER THE WEEKEND WITH A WEAK SYSTEM BRUSHING THE AREA. A WARM
FRONT WILL BRING STEADY RAIN BACK TO WESTERN WASHINGTON TUESDAY.
SHORT TERM /TODAY THROUGH FRIDAY/
SATELLITE IMAGERY SHOWS ATMOSPHERIC RIVER OVER THE NORTHERN HALF
OF WESTERN WASHINGTON EARLY THIS MORNING. RAIN SHADOW IN THE
CENTRAL PUGET SOUND HAS GOTTEN STRONGER IN THE LAST COUPLE OF
HOURS BRINGING ABOUT AN END TO THE RAIN BETWEEN TACOMA AND
EVERETT. UNDER CLOUDY SKIES TEMPERATURES WERE MILD, MOSTLY IN
THE LOWER 50S, AT 3 AM/10Z.
ATMOSPHERIC RIVER REMAINING AIMED AT MOST OF WESTERN WASHINGTON
THROUGH FRIDAY. THE RIVER WILL SAG SOUTH LATER TODAY INTO
TONIGHT. RAIN WILL REDEVELOP OVER THE SOUTHERN PORTION OF THE
AREA THIS AFTERNOON AND EVENING AND CONTINUE INTO FRIDAY. THE
RAIN SHADOW WILL ALSO GIVE WAY WITH SO MUCH MOISTURE IN THE AIR
MASS LATER THIS MORNING WITH RAIN AT TIMES FOR THE CENTRAL PUGET
SOUND INTO FRIDAY. EARLY MODEL RUNS INDICATED AN INCREASE IN THE
MOISTURE FRIDAY BUT THE CURRENT FORECAST HAS IVT VALUES BETWEEN
500-700 KG/M/S UNTIL THE RIVER MOVES OUT OF THE AREA. FRONTAL
BOUNDARY STALLED TO THE NORTH THROUGH THE PERIOD KEEPING BREEZY
CONDITIONS AT TIME OVER THE NORTHWEST INTERIOR. SNOW LEVELS
BETWEEN 7000 AND 8500 FEET THROUGH FRIDAY. NOT MUCH CHANGE IN
TEMPERATURES WITH HIGHS IN THE MID 50S AND LOWS IN THE MID 40S
TO LOWER 50S. RECORD HIGH MINIMUM TEMPERATURES ARE POSSIBLE
TODAY. FELTON
LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/
COLD FRONT MOVING THROUGH FRIDAY EVENING BRINGING ABOUT AN END
TO THE ATMOSPHERIC RIVER. RAIN GIVING WAY TO SHOWERS WITH SNOW
LEVELS DROPPING QUICKLY DOWN TO AROUND 4000 FEET. BREEZY
CONDITIONS WITH THE FRONTAL PASSAGE.
LITTLE CHANGE IN THE MODEL SOLUTIONS FOR THE WEEKEND WITH ZONAL
FLOW ALOFT OVER WESTERN WASHINGTON AND A WEATHER SYSTEM MOVING
BY TO THE NORTH. THIS WILL KEEP A CHANCE OF SHOWERS IN THE
FORECAST. SNOW LEVELS CONTINUING TO DROP BOTTOMING OUT BETWEEN
1500 TO 2000 FEET SATURDAY NIGHT INTO SUNDAY MORNING. MOISTURE
WILL BE LIMITED KEEPING NEW SNOW AMOUNTS IN THE MOUNTAINS AT A
MINIMUM.
BEST CHANCE AT A COMPLETELY DRY DAY MONDAY WITH SOME WEAK UPPER
LEVEL RIDGING OUT AHEAD OF THE NEXT FRONTAL SYSTEM. TIMING ON
THIS FEATURE HAS SLOWED DOWN A LITTLE BUT THE WARM FRONT IS STILL
TIMED INTO THE AREA TUESDAY BRINGING RAIN BACK INTO THE
FORECAST. HIGHS NEAR 50 WITH MID 50S POSSIBLE MONDAY. LOWS WILL
COOL SIGNIFICANTLY BEHIND THE FRONT WITH THE COLDER LOCATIONS
BELOW FREEZING SUNDAY AND MONDAY MORNINGS. INCREASING CLOUDS
MONDAY NIGHT KEEPING LOWS IN THE MID 30S TO LOWER 40S. FELTON
AVIATION
STRONG WESTERLY FLOW ALOFT WILL CONTINUE ACROSS WESTERN WASHINGTON
AS A MOIST AIR MASS CONTINUES TO FUNNEL RAIN INTO THE REGION AHEAD
OF A STALLED FRONTAL BOUNDARY OVER BRITISH COLUMBIA. A MIX OF MVFR
AND TEMPO IFR/LIFR CONDITIONS IN LIGHT TO MODERATE RAIN WILL PERSIST
THROUGH THE DAY.
KSEA...MVFR CEILINGS IN LIGHT RAIN ARE EXPECTED THROUGH THE DAY WITH
TEMPO IFR THIS MORNING. SOME GUIDANCE IS SUGGESTING SOME BRIEF
IMPROVEMENT TO VFR LATE THIS AFTERNOON, BUT OVERALL CONFIDENCE IN
THIS OUTCOME IS LOW. SURFACE WINDS SOUTHERLY 5 TO 8 KNOTS RISING TO
8 TO 12 KNOTS THIS AFTERNOON. 27
MARINE
PERIODS OF SMALL CRAFT ADVISORY STRENGTH SOUTHERLIES WILL CONTINUE
ACROSS THE WATERS INTO LATE WEEK AS A STALLED FRONTAL BOUNDARY NORTH
OF VANCOUVER ISLAND EVENTUALLY SHIFTS SOUTHEASTWARD ON FRIDAY.
ONSHORE FLOW WILL DEVELOP BEHIND THE FRONT FRIDAY NIGHT INTO
SATURDAY THEN EASE OVER THE WEEKEND AS A BUILDING SURFACE RIDGE
OFFSHORE MOVES INLAND. 27
HYDROLOGY
ATMOSPHERIC RIVER OVER THE AREA STILL EXPECTED TO CAUSE POSSIBLE
FLOODING PROBLEMS FOR RIVERS FLOWING OUT OF THE CASCADES FROM
KING COUNTY NORTHWARD AND THE SKOKOMISH RIVER IN MASON COUNTY.
RAINFALL AMOUNTS OVERNIGHT HAVE BEEN LESS THAN PREDICTED. THERE
IS A FEW ONE INCH BULLSEYES IN THE CASCADES FROM KING COUNTY
NORTHWARD BUT MOST OF THE AREA REPORTING 0.30 TO 0.50 INCHES IN
THE LAST 6 HOURS. IN THE CASCADES SOUTH OF KING COUNTY RAINFALL
AMOUNTS HAVE BEEN 0.30 INCHES OR LESS. OLYMPICS RAINFALL AMOUNTS
ALSO NOT IMPRESSIVE IN THE LAST 6 HOURS, 0.30 INCHES TO 0.50
INCHES.
RAINFALL AMOUNTS FORECAST FOR TODAY THROUGH FRIDAY EVENING, 4 TO
7 INCHES IN THE NORTH CASCADES, 3 TO 5 INCHES FOR THE OLYMPICS
AND THE COAST AND 1 TO 2 INCHES FOR THE INTERIOR. SNOW LEVELS
REMAINING IN THE 7000 TO 8500 FOOT RANGE.
FLOOD WARNINGS WERE ISSUED LAST NIGHT FOR THE SNOQUALMIE RIVER
BOTH NEAR THE FALLS AND AT CARNATION. AT THAT TIME THE RIVER
HAD A CHANCE TO REACH FLOOD STAGE EARLY THIS MORNING. THE LOWER
RAINFALL AMOUNTS OVERNIGHT HAVE SLOWED THE RIVER RISES. STILL
EXPECTING THE RIVER TO REACH FLOOD STAGE JUST LATER TODAY
INSTEAD OF THIS MORNING.
FLOOD WATCH FOR KING, SNOHOMISH, SKAGIT, WHATCOM AND MASON
COUNTIES REMAINING IN EFFECT. RAINFALL RATES IN THE MOUNTAINS
INCREASING LATER TODAY WITH FLOODING POSSIBLE ON BUT NOT LIMITED
TO THE FOLLOWING RIVERS TOLT, SNOHOMISH, PILCHUCK, SKAGIT,
NOOKSACK AND OF COURSE THE FLOOD PRONE SKOKOMISH THURSDAY OR
FRIDAY.
SO FAR IN MARCH SEATTLE HAS HAD TWO ONE INCH PLUS RAIN DAYS (
1.15 INCHES ON THE 11TH AND 1.22 INCHES ON THE 13TH ). IN 81
YEARS OF RECORDS AT SEATTLE-TACOMA AIRPORT THERE HAS ONLY BEEN
ONE MARCH WITH THREE ONE INCH PLUS RAIN DAYS, THE RECORD
SETTING YEAR OF 2014 ( 9.44 INCHES ). THIS YEAR MAKES THE 4TH
MARCH ON RECORD WITH TWO ONE INCH PLUS DAYS. INCLUDING THIS YEAR
THERE HAVE BEEN 23 ONE INCH PLUS RAIN DAYS IN MARCH AT SEATTLE-
TACOMA AIRPORT. FELTON
SEW WATCHES/WARNINGS/ADVISORIES
WA...FLOOD WATCH FROM 1 PM PDT THIS 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 FROM NOON TODAY TO 5 PM PDT THURSDAY FOR
WEST ENTRANCE U.S. WATERS STRAIT OF JUAN DE FUCA.
SMALL CRAFT ADVISORY FROM 4 PM THIS AFTERNOON TO 5 PM PDT
THURSDAY FOR NORTHERN INLAND WATERS INCLUDING THE SAN
JUAN ISLANDS-PUGET SOUND AND HOOD CANAL.
SMALL CRAFT ADVISORY FROM 2 PM THIS AFTERNOON TO 5 PM PDT
THURSDAY FOR ADMIRALTY INLET.
SMALL CRAFT ADVISORY UNTIL 5 PM PDT THURSDAY 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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