108
FXUS66 KSEW 172343
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
343 PM PST TUE DEC 17 2024
SYNOPSIS
ACTIVE WEATHER WILL REMAIN FOR THE NEXT SEVERAL DAYS
ACROSS WESTERN WASHINGTON. AN ATMOSPHERIC RIVER WILL BRING
HEAVIER RAIN, GUSTY WINDS, AND MOUNTAIN WINTER WEATHER TODAY
THROUGH EARLY WEDNESDAY. ADDITIONAL SYSTEMS WILL MOVE ACROSS THE
AREA AT TIMES INTO THE BEGINNING OF NEXT WEEK.
SHORT TERM /TONIGHT THROUGH FRIDAY/
WE'RE WELL INTO A PERIOD
OF ACTIVE WEATHER IN THE PNW. AN OCCLUDED LOW CENTER JUST WEST OF
HAIDA GWAII IS STEERING A WEAK ATMOSPHERIC RIVER INTO WESTERN
WASHINGTON WITH PWAT VALUES UP TO 1.20-1.30" GIVEN RECENT RAP
ANALYSIS. THIS FEATURE IS EXPECTED TO PERSIST INTO WEDNESDAY
MORNING WITH UP TO 2.00-4.00" INCHES OF RAINFALL FOR THE CASCADES
AND 3.00-6.00" FOR THE OLYMPICS. 1.00-3.00" IS AT PLAY FOR THE
COAST WITH LOWER AMOUNTS (0.50-2.00") FOR THE INTERIOR LOWLANDS
WITH RAIN SHADOWING HELPING TO TRIM DOWN THOSE TOTALS. HYDROLOGIC
FLOODING ALONG THE SKOKOMISH RIVER IS HAPPENING WITH MORE
INFORMATION PROVIDED BELOW IN THE HYDRO SECTION.
ALONG WITH RAINFALL, WINTRY PRECIPITATION IS ONGOING IN THE
MOUNTAINS WITH SNOW FALL UP OF 4.00-8.00" EXPECTED FOR THE PASSES
THIS AFTERNOON. HOWEVER, A WARM FRONT CURRENTLY ALONG THE COAST
WILL SPREAD INLAND THIS EVENING. THE PSL WIND PROFILER AT FORKS
SHOWS SNOW LEVELS NEAR 8,000 FT ON THE WESTERN FRINGE OF THE
OLYMPICS. THIS WARM COLUMN OF AIR EXTENDING TOWARDS THE CASCADES
WILL ACT IN CONCERT WITH COLD, SHALLOW AIR AT THE PASSES PROVIDED
BY EASTERLY WINDS. THIS SET UP WILL BRING A PERIOD OF FREEZING
RAIN THIS EVENING INTO TONIGHT UP ON THE MOUNTAINS. AN ONSHORE
SWITCH WILL BRING WARMER SURFACE TEMPERATURES TO THESE PARTS,
ALLOWING WARMER RAIN TO RETURN. ICE ACCUMULATIONS UP TO 0.10-0.20"
OF AN INCH IS POSSIBLE FOR TONIGHT AT THE PASSES.
WIND WILL ALSO BE OF CONCERN THIS AFTERNOON INTO EARLY WEDNESDAY
MORNING. THE SUB 990MB SURFACE LOW JUST WEST OF HAIDA GWAII HAS
HELPED TO TIGHTEN GRADIENTS AS IT INTERACTS WITH SURFACE HIGH
PRESSURE OVER THE INLAND NORTHWEST. AS A RESULT, A WIND ADVISORY
HAS BEEN ISSUED FOR ALL OF WESTERN WASHINGTON LOWLANDS BEGINNING
THIS EVENING INTO EARLY WEDNESDAY MORNING. HREF GUIDANCE INDICATES
A LARGE SWATH OF THE PROBABILITY FOR WIND GUSTS EXCEEDING 45 MPH
AROUND 70-80%. GUSTY WINDS COULD BLOW AROUND UNSECURED OBJECTS. A
HIGH WIND WARNING IS IN EFFECT ALONG THE COAST AS HREF
PROBABILITIES OF GUSTS EXCEEDING 55 MPH ARE PINGING AROUND 70-80%.
PRETTY SIGNIFICANT. DAMAGING WINDS CAN BLOW DOWN TREES AND POWER
LINES WITH WIDESPREAD POWER OUTAGES EXPECTED FOR AREAS IN THE HIGH
WIND WARNING FROM CAPE ELIZABETH TO LA PUSH, AND ALONG THE
IMMEDIATE COASTLINE. WINDS SHOULD SUBSIDE INTO WEDNESDAY MORNING.
IF THOSE IMPACTS AREN'T ENOUGH, COASTAL FLOODING IS AN ISSUE AS AN
ADVISORY IS IN EFFECT FOR THE COAST FOR MINOR FLOODING THROUGH
THIS EVENING. ADDITIONAL MINOR FLOODING IN POSSIBLE TOMORROW FOR
SAN JUAN COUNTY AND THE NORTHERN INTERIOR AROUND HIGH TIDE.
AS MENTIONED, RAINFALL AND WIND IS EXPECTED TO TAPER OFF INTO
WEDNESDAY AS A COLD FRONT PUSHES EAST OF THE CASCADES. HOWEVER, A
CONVERGENCE ZONE MAY LINGER ACROSS SNOHOMISH AND NORTHERN KING
COUNTIES WEDNESDAY MORNING FOR A BRIEF PERIOD OF HEAVIER RAINFALL
AFTER THE FRONTAL PASSAGE. UPPER-RIDGING WILL ALLOW FOR A BRIEF
SPELL OF DRIER WEATHER WEDNESDAY EVENING. BUT OF COURSE, IT WON'T
BE LONG LASTING AS DETERMINISTIC GUIDANCE HAS A WEAK FRONT
ENTERING ON THURSDAY WITH LIGHT RAIN. WE'LL RINSE AND REPEAT
THURSDAY NIGHT INTO FRIDAY WITH A SIMILAR PATTERN. HIGH
TEMPERATURES WILL TOP OUT IN THE 50S WITH LOWS GENERALLY IN THE
40S WITH SOME UPPER 30S IN THE SHORT TERM FORECAST.
MCMILLIAN
LONG TERM /SATURDAY THROUGH TUESDAY/
RIDGING BUILDS FURTHER ACROSS
THE INTERMOUNTAIN WEST INTO SATURDAY. HOWEVER, WESTERN WA WILL BE
ON THE WESTERN FRINGE OF THE UPPER RIDGE, ALLOWING FOR POPS LATER
IN THE WEEK. A FRONTAL SYSTEM MOVES TOWARDS THE PACIFIC NORTHWEST
LATER SATURDAY INTO SUNDAY, INCREASING THE RISK FOR LOWLAND RAIN
AND HIGHER ELEVATION MOUNTAIN SNOWFALL. THE ACTIVE PATTERN WILL
THEN CONTINUE INTO NEXT WEEK AS HIGHLIGHTED BY THE CPC WEEK-2
HAZARD OUTLOOK FOR A MODERATE RISK IN HEAVY PRECIPITATION, HIGH
WINDS, AND HEAVY MOUNTAIN SNOWFALL.
MCMILLIAN
AVIATION
SOUTHWESTERLY TO WEST FLOW ALOFT AS A FRONT MOVES
THROUGH W WA THIS AFTERNOON. STEADY RAIN HAS BEGUN MOVING
THROUGHOUT THE AREA TERMINALS, WITH CONDITIONS VARYING BETWEEN
MVFR/IFR. LOCALIZED SPOTS OF LIFR HAVE BEEN POSSIBLE WITH LOWER
VISIBILITIES DUE TO HEAVIER RAIN PASSING OVER TERMINALS. THIS
WILL CONTINUE TO BE THE TREND THROUGHOUT THE EVENING AND INTO THE
OVERNIGHT AS RAIN WILL LIKELY REDUCE VISIBILITIES AT TIMES BETWEEN
3-5SM, KEEPING CONDITIONS MVFR/IFR INTO WEDNESDAY MORNING.
SOUTHERLY WINDS WILL ALSO START TO INCREASE LATER THIS EVENING
STARTING WITH COASTAL TERMINALS, WITH THE HIGHEST WINDS EXPECTED
AT KHQM WITH GUSTS UPWARDS TO 40-50 KTS. SUSTAINED WINDS NEAR THE
INTERIOR TERMINALS RANGING AROUND 15 TO 25 KTS AND GUSTS UP TO 35
TO 40 KTS.
KSEA...MVFR CONDITIONS AT THE TERMINAL THIS AFTERNOON
AS MORE WIDESPREAD STEADY RAIN IMPACTS THE TERMINAL. WITH THIS
STEADY RAIN, CAN EXPECT VISIBILITY RESTRICTIONS RANGING FROM
3-5SM. A BOUNCE AROUND TO MVFR/IFR IS POSSIBLE THROUGHOUT THE
EVENING AND INTO WEDNESDAY MORNING AS RAIN PERSISTS. SOUTHERLY
WINDS WILL INCREASE LATER TONIGHT INTO WEDNESDAY MORNING, WITH
SUSTAINED WINDS 15 TO 25 KTS AND GUSTS POSSIBLE UP TO 30 TO 40
KTS. THE HIGHEST WINDS WILL PEAK AROUND 05Z-09Z, WITH WIND SPEEDS
GRADUALLY DECREASING BY 12Z WEDNESDAY.
MAZURKIEWICZ
MARINE
A FRONT WILL CONTINUE TO MOVE THROUGH THE AREA WATERS
THIS EVENING INTO WEDNESDAY MORNING, BRINGING ELEVATED WINDS AND
SEAS. SOUTHERLY WINDS WILL CONTINUE TO INCREASE THROUGH THIS
EVENING, WITH GALE FORCE WINDS EXPECTED THROUGH ALL OF THE COASTAL
WATER ZONES, AND ALL OF THE INTERIOR WATER ZONES. THE ONLY CHANGE
FROM THE PREVIOUS FORECAST WAS THE UPGRADE FROM A SMALL CRAFT
ADVISORY TO A GALE WARNING FOR THE PUGET SOUND AND HOOD CANAL
ZONE. THESE SOUTHERLY WINDS WILL TRANSITION WESTERLY ONCE THE
FRONT PASSES WEDNESDAY MORNING, WITH ADDITIONAL HEADLINES LIKELY
NEEDED AFTER THE INITIAL SOUTHERLY WIND DIRECTION.
ACTIVE WEATHER WILL ONLY CONTINUE AS ANOTHER SYSTEM ON THURSDAY
LOOKS TO DELIVER ANOTHER ROUND OF GUSTY WINDS OVER THE COASTAL
WATERS, WITH PERHAPS ANOTHER IMPACTFUL SYSTEM EARLY NEXT WEEK.
COASTAL SEAS WILL BUILD THIS AFTERNOON UPWARDS TO AROUND 13 TO 16
FEET, DECREASING INTO WEDNESDAY BUT REMAINING ABOVE 10 FEET.
LATEST GUIDANCE SEEMS TO BE HINTING AT SEAS REACHING 20 FEET EARLY
NEXT WEEK AS ADDITIONAL SYSTEMS IMPACT THE AREA.
MAZURKIEWICZ
HYDROLOGY
AN ATMOSPHERIC RIVER IMPACTING THE REGION WILL BRING
ABOUT 3 TO 5 INCHES OF RAIN TO THE OLYMPIC PENINSULA AND PORTIONS
OF THE NORTH CASCADES TONIGHT INTO WEDNESDAY AS SNOW LEVELS RISE
TO 7000 TO 8000 FT. AT THIS TIME, ONLY THE SKOKOMISH RIVER IS
EXPECTED TO RISE INTO FLOOD STAGE. HOWEVER, EXPECT OTHER AREA
RIVERS ALONG THE CENTRAL AND NORTH CASCADES TO EXPERIENCE RISES
AND APPROACH ACTION STAGE.
ADDITIONAL INCOMING PRECIPITATION FROM WET SYSTEMS LATER IN THE
WEEK AND INTO NEXT WEEK WILL MAINTAIN THE THREAT OF RIVER FLOODING
ACROSS WESTERN WASHINGTON, BUT MODELS CONTINUE TO SHOW LARGE
DISCREPANCIES AND THE FORECAST REMAINS UNCERTAIN AT THIS TIME.
14
SEW WATCHES/WARNINGS/ADVISORIES
WA...WIND ADVISORY FROM 4 PM THIS AFTERNOON TO 4 AM PST WEDNESDAY FOR
CENTRAL COAST-NORTH COAST-SAN JUAN COUNTY-WESTERN SKAGIT
COUNTY-WESTERN WHATCOM COUNTY.
WIND ADVISORY UNTIL 7 AM PST WEDNESDAY FOR ADMIRALTY INLET AREA.
FLOOD WATCH THROUGH LATE TONIGHT FOR HOOD CANAL AREA-LOWER
CHEHALIS VALLEY AREA-OLYMPICS.
WINTER WEATHER ADVISORY UNTIL 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 UNTIL 10 AM PST WEDNESDAY FOR GRAYS HARBOR
BAR.
GALE WARNING UNTIL 10 AM PST 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-EAST ENTRANCE U.S.
WATERS STRAIT OF JUAN DE FUCA-WEST ENTRANCE U.S. WATERS
STRAIT OF JUAN DE FUCA.
SMALL CRAFT ADVISORY UNTIL 10 PM PST THIS EVENING FOR CENTRAL
U.S. WATERS STRAIT OF JUAN DE FUCA.
GALE WARNING FROM 10 PM THIS EVENING TO 10 AM PST WEDNESDAY FOR
CENTRAL U.S. WATERS STRAIT OF JUAN DE FUCA.
GALE WARNING UNTIL 7 AM PST WEDNESDAY FOR NORTHERN INLAND WATERS
INCLUDING THE SAN JUAN ISLANDS.
SMALL CRAFT ADVISORY UNTIL 7 AM PST WEDNESDAY FOR PUGET SOUND
AND HOOD CANAL.
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