textproduct: Seattle/Tacoma

SYNOPSIS

A weak ridge overhead will maintain mostly dry conditions with a few showers across the southeast portions of the area tonight. The next disturbance will cross the area on Wednesday, bringing additional snow to the mountains and rain to the lowlands. After some shower linger later in the week, especially across the north, a trend toward cool and drier conditions emerge over the weekend and continue into the first half of next week.

SHORT TERM /TODAY THROUGH THURSDAY NIGHT/

Western Washington remains on the fringe of an elongated frontal system spanning down into Oregon. High clouds and light showers will continue to push to the southeast out of Lewis County tonight. Otherwise, outside of some low clouds in the mountains, much of the northwestern portions of the area remain under mostly clear skies tonight, except for a few clouds streaming in from the north. Low temperatures tonight in the mid 30s to around 40.

Another weather system will being to move in early Wednesday morning and persist across the area through early Friday. While most of the precipitation will be focused through British Columbia, the area will be on the southern fringe of this system. The majority of the precipitation will be focused on the northern Olympic Peninsula/northern Pacific coast, and the north Cascades, primarily north of Stevens Pass. Through Friday morning, up to 1 ft of snow will be possible mainly in the higher-elevation back country and at Mt. Baker Ski Area. At Stevens Pass, 4-6" is the expected range. With snow levels rising about 3500 ft on Thursday, Snoqualmie Pass will allow for a period of rain, which will limit expected accumulations and impacts there.

Wednesday and Thursday will be similar in terms of the temperatures and the winds. Highs will in the upper 40s to low 50s. Lows in the mid 30s to low 40s. Winds will be breezy, with speeds 15 to 25 mph with gusts 25 to 35 mph possible. Winds will begin to taper off Thursday afternoon.

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LONG TERM /FRIDAY THROUGH TUESDAY/

Ensemble guidance remains in good agreement suggesting another round of high pressure building over the region as an upper low cuts off over California late this week into the weekend, promoting a trend toward drier and cooler weather as the air mass dries out and skies clear. Most likely temperatures drop to around the freezing mark in the city centers and into the upper 20s elsewhere.

AVIATION

West to northwest flow will persist aloft with weak troughing aloft. Clouds over the southeastern portion of the area will continue to depart to the southeast tonight. Clouds will also begin to fill in overnight across the area as the next system moves in from the north. Precipitation will be mainly be confined to to the mountains, but this will bring in enough moisture for MVFR cigs to develop across most of the area. Models are beginning to hint that even IFR cigs or areas of patchy fog may also be possible going into the hours near sunrise Wednesday morning. Improvement to VFR will be slow through the morning but a return is expected by Wednesday afternoon.

Northerly winds will ease tonight before switching to light southerly overnight, increasing up to 8 to 15 kt by Wednesday morning. Gusts up to 20 to 25 kt will be possible.

KSEA...VFR conditions will prevail through late this evening. Increased moisture from an incoming weather system will allow for ceilings to redevelop and lower. The current most likely scenario is a solid MVFR deck, but if we remain scattered/broken overnight that may introduce areas of lower cigs and isolated areas of fog. Probabilities for IFR cigs are generally at around 5-10% between 11-17Z Wed and 20-30% for MVFR. A slow improvement to VFR is expected through the late morning Wednesday. North winds have started to ease this evening and will switch to the south overnight. Winds will increase through the morning, up to 8-15 kt with gusts up to 20 kt by 18-21Z Wed.

MARINE

Marine conditions have largely subsided today with weak high pressure temporarily over the waters. Winds will likely increase through the Strait of Juan de Fuca over the next few hours and persist into Wednesday with low-end advisory speeds developing overnight. Expect a possible area to expand later Wednesday across the northern coastal waters as well as the Strait into Thursday as a stronger disturbance passes across southern B.C. Seas will also build near to 10 ft with a mix of a larger westerly swell and a smaller southerly wave group.

HYDROLOGY

No river flooding is expected during the next seven days.

SEW WATCHES/WARNINGS/ADVISORIES

WA...Winter Weather Advisory from 4 AM Wednesday to 4 AM PST Friday for Cascades of Snohomish and Northern King Counties- Cascades of Whatcom and Skagit Counties.

PZ...Small Craft Advisory until 4 PM PST Wednesday for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.