textproduct: Seattle/Tacoma

SYNOPSIS

Upper level trough over Western Washington keeping cool unsettled weather over the area through tonight. Next system arriving Tuesday. A much stronger, atmospheric river based system arrives Wednesday and Wednesday night bringing heavy snow to the mountains and rain and locally windy conditions to the lowlands. The wet weather pattern will remain intact into the weekend.

SHORT TERM /TODAY THROUGH WEDNESDAY/

Scattered showers persist this morning, with convergence activity waning in NE King County. Some rain and snow mixed showers could be possible through the morning, becoming more rain based this afternoon. No other major forecast changes have been made this morning, and the rest of the previous discussion can be found below. An update to the aviation sections has also been provided.

Scattered showers continuing this evening. Shower activity decreasing overnight as a weak upper level ridge moves in ahead of the next frontal system. Another convergence zone possible over Skagit or Snohomish county moving into the Cascades overnight. Heaviest snowfall in the mountains with the convergence. Another 7 to 9 inches possible. Outside of the convergence new snow amounts mostly in the two to five inch range. Lows Tuesday morning in the upper 20s to mid 30s.

Snow levels will be near the surface Tuesday morning but shower activity will be minimal. Rain out ahead of the next system reaching the coast in the afternoon spreading inland late in the day. Highs again in the mid 40s.

Rain over the entire area Tuesday night into Wednesday. Snow heavy at times in the mountains. Snow levels between 1000 and 1500 feet Tuesday night rising to 2000 to 3500 feet Wednesday. This will be the beginning of prolonged period of significant snows in the mountains. Lows in the mid 30s to lower 40s. Highs in the lower 50s.

Winter storm warning remaining in effect until 5 am Tuesday for the Cascades from North King county northward. An additional 8 to 16 inches of new snow possible with the higher amounts near Stevens Pass.

Winter weather advisory in effect for the remainder of the Cascades through Tuesday afternoon for the possibility of 6 to 10 inches of new snow.

A winter weather advisory remains in effect for the Western Strait of Juan de fuca for possible 1 to 4 inch snow accumulations in the Lake Crescent area and along Highway 101 heading towards the north coast.

A winter weather advisory is also in effect for the foothills and valleys of Snohomish and Northern King county with the convergence zones producing up to six inches of new snow through Tuesday morning.

A winter storm watch remains in effect for the Cascades and Olympics from later Tuesday into Friday for another 2 to 4 feet of new snow possible. Blizzard conditions are also possible later Wednesday into Wednesday night. Felton

LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/

System moving through Wednesday night with a strong winds possible along the coast and Strait of Juan de Fuca into Whidbey Island. Windy conditions elsewhere. Its possible a blizzard warning may be needed for the Cascades.

Potential atmospheric river arriving Thursday with the river aimed at Western Washington at least through Friday. Snow levels will rise but not too much, into the 3500-4500 foot range. New snow totals will be measured in feet not inches.

Models in fairly good agreement that a weak upper level ridge will build offshore cutting the atmospheric river off and pushing the system south of the area Saturday. The break in the precipitation will be short lived with another front approaching Sunday.

Extended models beyond day 7 are in good agreement with another atmospheric river reaching the west coast Monday into Tuesday. Some solutions have this feature north of the area and some have it right over Western Washington. Heavy snow in the mountains and rain in the lowlands followed by a warm heavy rain is a scenario where the rivers will need watching. Felton

AVIATION

Zonal flow aloft through the TAF period. Post- frontal onshore flow persists at the surface. VFR across most terminals so far this morning. Puget Sound terminals (KBFI, KPAE, KSEA) may continue to see instances of MVFR cigs due to convergence zone activity meander across King/Snohomish counties before petering out around 15-18z. Mostly VFR into the day on Monday as well but can't rule out intermittent low cigs/vis from passing showers. A convergence zones looks to redevelop again between 22z Monday and 00z Tuesday, likely bringing MVFR cigs to KPAE again. Breezy S/SW winds increasing during the afternoon to 20-30 kt then decreasing after 00z.

KSEA...A mix of VFR/MVFR cigs due to a convergence zone until 15-18z. Afterwards, mainly VFR throughout the rest of the day aside from brief low cigs/vis from passing showers. S/SW winds this morning between 8-10 kt, increasing Monday afternoon with gusts up to 25 to 30 kt possible. Gusts decrease around 00-02z Tuesday. NBM shows 40- 50% chance of MVFR cigs redeveloping after 00z Tuesday as due to convergence zone activity reemerging. A mix of VFR/MVFR again into Tuesday morning.

33/McMillian

MARINE

Mostly onshore flow through midweek and likely strong at times. This has resulted in SCA being in effect through the Strait of Juan de Fuca. West winds will also remain elevated for the Coastal Waters before easing briefly by Monday night. A stronger weather system will move across the waters Wednesday into Thursday, resulting in additional headlines. Confidence is increasing in gale force winds on Wednesday for the Coastal Waters, with the probability of gales wind gusts ranging between 50 to 70% for the interior waters on Wednesday. Winds will remain elevated, but slowly ease Thursday into late week.

Seas will range 9 to 12 feet through Tuesday. Seas will then build Wednesday to 14 to 17 ft over the Coastal Waters before falling between 10 ft by Thursday morning and remain that way through the remainder of the week.

McMillian

HYDROLOGY

Heavy precipitation, combined with rising snow levels, will bring increased flows on the Skokomish River beginning later Tuesday. It will be a tough call on the Skokomish River with snow levels only rising to around 3500 feet. The current river forecast has the Skokomish going over flood stage Wednesday. Elsewhere, river levels will rise, however, additional river flooding is not expected over the next seven days. Felton

SEW WATCHES/WARNINGS/ADVISORIES

WA...Winter Storm Warning until 5 AM PDT Tuesday for Cascades of Snohomish and Northern King Counties-Cascades of Whatcom and Skagit Counties.

Winter Storm Watch from late Tuesday night through Friday morning for Cascades of Pierce and Lewis Counties- Cascades of Snohomish and Northern King Counties-Cascades of Southern King County-Cascades of Whatcom and Skagit Counties.

Winter Weather Advisory until 5 PM PDT Tuesday for Cascades of Pierce and Lewis Counties-Cascades of Southern King County.

Winter Weather Advisory until 11 AM PDT Tuesday for Foothills and Valleys of Snohomish and Northern King Counties-Lake Crescent Area Including US 101-Western Strait of Juan de Fuca.

Winter Storm Watch from Tuesday afternoon through Friday morning for Olympics.

PZ...Small Craft Advisory until 5 PM PDT this afternoon for Grays Harbor Bar.

Small Craft Advisory until 11 PM PDT this evening for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory until 5 PM PDT Tuesday 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.