255
FXUS66 KSEW 162305
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
305 PM PST MON DEC 16 2024
SYNOPSIS
AN ACTIVE WEATHER PATTERN IS EXPECTED TO IMPACT
THE REGION OVER THE NEXT ONE TO TWO WEEKS. THE NEXT SYSTEM WILL
MOVE THROUGH THE AREA TUESDAY INTO EARLY WEDNESDAY BRINGING
WIDESPREAD MODERATE LOWLAND RAIN, GUSTY WINDS, AS WELL AS MOUNTAIN
SNOW AND FREEZING RAIN. ADDITIONAL WARM AND WET SYSTEMS WILL MOVE
THROUGH THE REGION THROUGH NEXT WEEKEND AND BEYOND, GRADUALLY
INCREASING THE RISK OF RIVER FLOODING.
SHORT TERM /TONIGHT THROUGH THURSDAY/
WIDESPREAD STRATIFORM
PRECIPITATION HAS ENDED ACROSS WESTERN WASHINGTON WITH JUST A FEW
ISOLATED AREAS OF SHOWERS MOVING NORTHEAST ACROSS THE REGION.
THE NEXT WEATHER SYSTEM WILL BEGIN TO IMPACT THE REGION
OVERNIGHT, WITH A LEADING BAND OF LIGHT TO MODERATE PRECIPITATION
SPREADING OVER SOUTHWESTERN WA BEFORE DISSIPATING. THIS WILL BE
FOLLOWED BY A MORE POTENT WARM FRONT THAT WILL SPREAD FROM SW TO
NE ACROSS THE REGION LATER TUESDAY MORNING THROUGH TUESDAY
AFTERNOON. MODERATE TO OCCASIONALLY HEAVY RAINFALL IS EXPECTED
ACROSS MUCH OF THE REGION WITH THIS SYSTEM AS WELL AS RAPIDLY
INCREASING SNOW LEVELS (GENERALLY FROM 2000-2500 FEET RISING TO
7000-8000 FEET). RAINFALL COULD RESULT IN AREAS OF STANDING WATER
DURING THE TUESDAY AFTERNOON/EVENING COMMUTE. MEANWHILE, AT THE
PASSES, EASTERLY WINDS WILL KEEP TEMPERATURES COOL. THIS WILL
RESULT IN A GRADUAL TRANSITION OF PRECIPITATION FROM SNOW TO
FREEZING RAIN AND EVENTUALLY RAIN ALONG AND EAST OF THE CASCADE
CREST TUESDAY AFTERNOON THROUGH WEDNESDAY MORNING. WHILE THE MOST
LIKELY SCENARIO IS ICE ACCUMULATIONS ON THE ORDER OF 0.1-0.2
INCHES AT PASS LEVEL, HIGHER AMOUNTS ON THE ORDER OF 0.5 INCHES
CANNOT BE RULED OUT DEPENDING ON HOW LONG THE SUBFREEZING
TEMPERATURES REMAIN AT THE SURFACE. A WINTER WEATHER ADVISORY HAS
BEEN ISSUED BOTH FOR THE SNOW AT THE ONSET OF THIS SYSTEM AS WELL
AS THE FREEZING RAIN THROUGH EARLY WEDNESDAY MORNING.
THIS SYSTEM WILL ALSO BRING BREEZY TO WINDY CONDITIONS ACROSS THE
AREA. CURRENTLY THE STRONGEST WINDS ARE EXPECTED ALONG THE CENTRAL
AND SOUTHERN COAST WHERE GUSTS TO AROUND 45 MPH ARE EXPECTED,
MAINLY ALONG THE COASTAL COMMUNITIES. A WIND ADVISORY HAS BEEN
ISSUED FOR THIS AREA.
FORTUNATELY, THE RISK OF COASTAL FLOODING WILL DECREASE TUESDAY.
HOWEVER, A SLIGHTLY UPTICK IN RISK IS POSSIBLE WEDNESDAY AS THE
SURFACE LOW MAKES ITS CLOSEST APPROACH TO WA. STILL, ANY FLOODING
CURRENTLY APPEARS AS IF IT WOULD PEAK IN THE MINOR CATEGORY WITH
HIGH TIDES WEDNESDAY. THE RISK THEN VERY SLOWLY DECREASES THROUGH
THE REST OF THE WEEK.
TRANSIENT RIDGING LOOKS TO MOVE ACROSS THE REGION LATE WEDNESDAY
INTO THURSDAY MORNING, KEEPING THIS PERIOD RELATIVELY DRY.
HOWEVER, THE BREAK WILL BE SHORT-LIVED AS THE NEXT WAVE BEGINS TO
SPREAD PRECIPITATION ACROSS NW WA BY THE AFTERNOON.
LONG TERM /FRIDAY THROUGH MONDAY/
THE LONG TERM PERIOD WILL BE
CHARACTERIZED BY A MEAN TROUGH JUST OFFSHORE, DIRECTING A SERIES
OF WAVES ACROSS THE REGION FRIDAY THROUGH AT LEAST EARLY NEXT
WEEK. EACH WAVE WILL HAVE THE POTENTIAL TO HAVE A GOOD TAP OF
MOISTURE PRODUCING ATMOSPHERIC RIVER CONDITIONS. WITH EACH
SUCCESSIVE WAVE, THE RISK OF MORE WIDESPREAD RIVER FLOODING AND
LANDSLIDES WILL INCREASE. AT THIS POINT IN TIME, IT'S DIFFICULT TO
PIN DOWN EXACTLY WHEN AND WHERE THESE CONCERNS WOULD BE GREATEST.
BUT FOR THE MOMENT, THE SUNDAY TIMEFRAME HAS THE HIGHEST POTENTIAL
FOR HEAVY PRECIPITATION AND STRONG WINDS.
IT'S ALSO WORTH NOTING THAT THE CPC WEEK-2 OUTLOOK IS CURRENTLY
HIGHLIGHTING A MODERATE (40%) RISK OF HEAVY PRECIPITATION, HIGH
WINDS, AND HEAVY MOUNTAIN SNOW THROUGH MOST OF NEXT WEEK.
-WOLCOTT-
AVIATION
SOUTH TO SOUTHWESTERLY FLOW ALOFT OVER W WA TODAY WITH
AN UPPER LEVEL TROUGH JUST OFF THE COAST AND GRADUALLY CREEPING
EASTWARD. SOUTH TO SOUTHEASTERLY SURFACE WINDS GENERALLY 5-10 KTS.
PAE IS RUNNING A LITTLE FASTER, MAINLY 10-15 KTS WITH GUSTS UP TO 25
WHILE HQM DIFFERS IN BOTH DIRECTION AND SPEED, EASTERLY AT 8-12 KTS.
MIX OF MVFR TO VFR CIGS OVER THE AREA THIS AFTERNOON. TERMINALS THAT
ARE REPORTING VFR HAVE SEEN MOST OF THE LOWER CLOUDS LIFT WITH ONLY
MID TO HIGH LEVEL CLOUDS IN PLACE. THAT SAID, FOR MVFR LOCATIONS,
LOW CLOUDS STILL LINGERING A BIT LONGER THAN EXPECTED, ALTHOUGH
CONDITIONS ARE STILL EXPECTED TO LIFT BY EARLY EVENING AND REMAIN
THERE INTO TONIGHT. CLM AND PWT PROVING STUBBORN WITH IFR
CONTINUING...AND WITH LITTLE PROGRESS BEING MADE, IT IS POSSIBLE
THEY MAY ONLY RECOVER TO MVFR UNTIL FALLING AGAIN TONIGHT AHEAD OF
THE NEXT INCOMING SYSTEM. SAID INCOMING SYSTEM COMBINED WITH PLENTY
OF LOW LEVEL MOISTURE FROM EARLIER RAINS WILL BRING CIGS AREAWIDE
BACK DOWN INTO AT LEAST MVFR TONIGHT, WITH PRECIP TUESDAY KEEPING
THEM THERE FOR THE REMAINDER OF THE TAF PERIOD.
KSEA...VFR CONDITIONS IN PLACE THROUGH THIS EVENING. CIGS ERODING
OVERNIGHT DOWN INTO MVFR AFTER 06Z AS NEXT SYSTEM BEGINS TO IMPACT
THE AREA, LOWERING FURTHER TO LOW-END MVFR AS RAIN BECOMES MORE
CATEGORICAL BY LATE TUESDAY MORNING. SURFACE WINDS REMAINING LARGELY
SOUTHEASTERLY FOR THE TAF PERIOD WITH SPEEDS 5-10 KTS, BUT IT IS
WORTH NOTING THAT THERE IS A 5-HOUR WINDOW OF EASTERLIES AFTER 01Z
THIS EVENING.
18
MARINE
NO WIND-DRIVEN HEADLINES IN PLACE AT THIS TIME, HOWEVER
SEAS OVER THE COASTAL WATERS, ESPECIALLY THE OUTER COASTAL WATERS,
REMAIN RIGHT AROUND THE THRESHOLD, OR JUST A LITTLE OVER, FOR SCA
FOR WAVES...AND AS SUCH, THAT HEADLINE WILL REMAIN IN PLACE.
INCOMING WEATHER SYSTEM FOR TUESDAY WILL PROVIDE A BOOST FOR BOTH
WINDS AND WAVES OVER THE COASTAL WATERS, AND HAVE OPTED FOR
EXTENSIONS FOR THE AFTERNOON FORECAST PACKAGE FOR INNER COASTAL
WATERS. FOR THE OUTER COASTAL WATERS, MODELS REMAIN CONSISTENT ON
GALE FORCE WINDS AND AS SUCH HAVE OPTED FOR A GALE WATCH FOR THAT
AREA. INCREASING SOUTHERLIES TUESDAY NIGHT MAY ALLOW FOR AN AREAL
EXPANSION TO INCLUDE AT LEAST THE EAST STRAIT AND ITS ADJACENT
WATERS. SOLUTIONS REMAIN CONSISTENT THAT SCA WINDS SHOULD EMERGE NOT
ONLY FOR THE EAST ENTRANCE, BUT ALSO THE ADJACENT WATERS OF
ADMIRALTY INLET AND THE NORTHERN INLAND WATERS. DID NOT INCLUDE THIS
HEADLINE WITH AFTERNOON ISSUANCE AS IT FALLS JUST OUTSIDE 24-HOUR
THRESHOLD, BUT WILL ADVISE FUTURE SHIFTS ON THIS PROSPECT.
MULTIPLE SYSTEMS ARE EXPECTED TO MOVE OVER THE WATERS THROUGHOUT THE
WEEK KEEPING WAVES ABOVE 10 FT AND MORE WINDS FALLING UNDER SMALL
CRAFT CRITERIA. MODEL GUIDANCE DOES HINT AT ANOTHER STRONG SYSTEM
COMING AT THE END OF THE WEEK WITH WAVES POTENTIALLY BUILDING ABOVE
20 FT AND ANOTHER ROUND OF GALE FORCE WINDS.
18
HYDROLOGY
ADDITIONAL PRECIPITATION THROUGH TUESDAY MORNING
AHEAD OF AN INCOMING ATMOSPHERIC RIVER EVENT WILL CAUSE SIGNIFICANT
RISES TO AREA RIVERS. LATEST DETERMINISTIC FORECASTS SHOW INCOMING
LIQUID AMOUNTS OF 3 TO 5 INCHES OVER THE OLYMPIC PENINSULA BETWEEN
TUESDAY AND WEDNESDAY, WITH UP TO TO 4 INCHES OVER THE CASCADES.
SNOW LEVELS WILL ALSO BE ELEVATED DURING THIS EVENT, LIFTING AS
HIGH AS 7000-8000 FT TUESDAY NIGHT. THIS AMOUNT OF RAINFALL HAS
THE POTENTIAL FOR PRODUCING FLOODING. THE EXACT DETAILS OF THIS
MID-WEEK SYSTEM REMAIN UNCERTAIN, BUT AT THIS TIME THE SKOKOMISH
RIVER IS FORECAST TO ENTER MODERATE FLOOD STAGE ON WEDNESDAY WITH
OTHER AREA RIVERS APPROACHING OR REACHING ACTION STAGE.
ADDITIONAL INCOMING ATMOSPHERIC RIVER PRODUCING PRECIPITATION
TOWARDS THE END OF THE WEEK INTO NEXT WEEK MAINTAINS THE THREAT OF
RIVER FLOODING ACROSS WESTERN WASHINGTON, BUT MODELS CONTINUE TO
SHOW LARGE DIFFERENCES AND THE FORECAST IS UNCERTAIN. JBB/JD
SEW WATCHES/WARNINGS/ADVISORIES
WA...COASTAL FLOOD ADVISORY UNTIL 4 PM PST THIS AFTERNOON FOR CENTRAL
COAST.
WIND ADVISORY FROM 4 PM TUESDAY TO 4 AM PST WEDNESDAY FOR
CENTRAL COAST.
WINTER WEATHER ADVISORY FROM 4 AM TUESDAY TO 4 AM PST WEDNESDAY
FOR WEST SLOPES NORTH CASCADES AND PASSES-WEST SLOPES NORTH
CENTRAL CASCADES AND PASSES-WEST SLOPES SOUTH CENTRAL
CASCADES AND PASSES.
PZ...SMALL CRAFT ADVISORY FROM 10 PM THIS EVENING TO 1 AM PST
WEDNESDAY FOR GRAYS HARBOR BAR.
SMALL CRAFT ADVISORY UNTIL 1 AM PST WEDNESDAY 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 UNTIL 4 PM PST TUESDAY 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.
GALE WATCH FROM TUESDAY AFTERNOON THROUGH LATE TUESDAY NIGHT 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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