Marine Weather and Tide Forecast for SeaTac, WA

SHORT TERM /TODAY THROUGH FRIDAY/
More rain is moving into western Washington early this morning per the radar imagery. Snow levels will start off high, but will drop late tonight and into early Thursday morning. A Winter Weather Advisory has been posted for the central and southern Washington Cascades that will go into effect later this morning and last into Thursday. Locations above 3500 feet will see between 7-9 inches of snow, with elevations above 4500 feet seeing up to a foot of snow by Thursday afternoon. Snowfall will likely be heaviest across the passes this afternoon into late tonight.

Today will also feature a slightly unstable atmosphere with a low risk of thunderstorms. The best chances will be along the coast, but the Storm Prediction Center has highlighted all of the state for inclusion in the general thunder risk category.
Post frontal convergence zone activity is forecast in the hi-res models starting along the King and Snohomish county border, sinking south this afternoon into southern King County. There is a slight chance (10-15%) of thunderstorm activity within the convergence zone this afternoon.

Conditions dry up for most locations outside of lingering mountain snow showers on Thursday with highs in the 40s. A decaying front will bring more rain and mountain snow to the area on Friday.

LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/
Scattered shower activity will linger on Friday and Saturday, with some breaks in between rounds of rain. A slightly wetter system seems poised to arrive on Sunday as the offshore ridge flattens out and shifts the track more into Washington. Winds will also increase area wide on Sunday and linger into Monday, but the magnitude of the wind speeds are going to vary a bit between now and then, but could suggest stronger winds through the Strait of Juan de Fuca and along the Pacific coast.

Wet conditions are generally favored through the start of next week.

21

AVIATION
Moist southwest flow over western WA this morning with MVFR/IFR conditions along the Pacific Coast as another band of rain moves inland alongside a cold front. Elsewhere, most inland terminals remain low end VFR to high end MVFR. Showers will continue throughout the day with onshore flow and a slight chance of thunderstorms. However, confidence is not high enough to include in any of the TAFs. A convergence zone is expected to set up over the Puget Sound this afternoon, potentially impacting KBFI/KSEA. Shower activity will decrease over the Cascades later this evening.

KSEA...VFR early this morning in rain showers and S/SW winds around 6-10 kt. Brief MVFR conditions may develop throughout the morning in heavier rain activity. A convergence zone is favored to form this afternoon and evening, with the potential to bring a northerly wind shift and a few lightning strikes.

15



MARINE
A cold front will cross area waters this morning, with increasing onshore flow this afternoon. The highest winds will be over the coastal waters and through the Strait of Juan de Fuca, where Small Craft Advisories are in effect. Seas will build to over 10 ft Wednesday night and remain elevated through Thursday as a larger swell train reaches the coast. The flow will remain onshore Friday and Saturday, with potential for additional SCA wind headlines as seas ease to around 5 to 7 feet. Additional systems Sunday and beyond may allow seas to build above 10 feet, with additional headlines possible.

33/15

HYDROLOGY
No river flooding is expected over the next seven days.

SEW WATCHES/WARNINGS/ADVISORIES
WA...Winter Weather Advisory until 10 AM PST Thursday for Cascades of Pierce and Lewis Counties-Cascades of Snohomish and Northern King Counties-Cascades of Southern King County.

PZ...Small Craft Advisory until 10 AM PST Thursday for West Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory from 4 PM this afternoon to 10 AM PST Thursday for Central U.S. Waters Strait Of Juan De Fuca- East Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory until 1 PM PST 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.