Several inches of rain expected around Western Washington into Saturday

An atmospheric river and the associated warm front will bring some of the strongest winds and heaviest rain of the season so far on Friday and Friday night.

It will rain in most areas at most times of the day Friday and into Friday evening before tapering to showers overnight into Saturday.

With the blast of moisture coming in from nearly due west, the immediate Seattle, Bremerton and Bellevue corridor should receive the least amount of rain from this system, owing to an Olympic Mountain “rain shadow” as the mountain range to the west blocks some of the heaviest precipitation and creates sinking air over the Central Sound.

Still, there will be some rain from time to time in this area.

North and south of the Central Sound, at the coast and in the mountains below 6,000 feet, rain will be very heavy, causing urban flooding from clogged storm drains and river flooding, especially along the Snoqualmie and Skokomish rivers, which should reach moderate flood stage Saturday.

Rainfall range by region:

  • Central Sound (including Kitsap, King, southern Snohomish, northern Pierce): 0.50-1.00″
  • Interior locations north of Everett and south of Tacoma: 1-3″
  • Coast: 2-4″
  • Foothills and west-facing slopes of the Olympics and Cascades: 3-6″ with isolated higher amounts
  • East of the Cascades: light amounts

Winds will gust in the 15-25 mph range Thursday evening into Friday morning with some gusts over 30 mph in spots.

There are wind advisories at the coast and over the Admiralty Inlet area from late Thursday afternoon and early evening until Friday morning. Gusts for these spots will be in the 40-50 mph range.

Overall, the strongest wind looks to start during the daylight hours Friday, and be particularly strong afternoon into mid-evening before subsiding late at night.

Winds around Puget Sound could gust in the 30-45 mph range for many locations, including our cities around the Sound.

This would be the strongest wind in many of these locations so far this fall, and with leaves on many trees still (soon to be stripped clean), that will add to the wind load.

Expect some power outages, tree damage and places where roads are impacted by debris.

At the coast, winds could touch 50 mph on Friday.

Down the Strait of Juan de Fuca and through Whidbey Island, it’ll be gusty Friday, but a late surge of westerly wind to 50+ mph could occur late Friday night into the wee hours of Saturday morning.

This surge of wind could impact parts of western Snohomish and Skagit counties too.

By Saturday morning at daybreak, the strongest winds will be over in most locations, except east of the Cascades.

Rain Thursday night into Friday morning will initially fall as snow at the passes for a few inches, but by daybreak Friday this will turn to rain and wash away any chance of snowy travel.

All locations except perhaps the peaks of the volcanoes will get heavy rain through most of this period.

We have a Winter Weather Advisory in effect for this evening in the North Cascades above 4,000 feet, where we could see 6 to 12 inches of snow before snow levels rise.

The weekend will be showery and colder with highs in the 40s in the lowlands.

We’ll likely have some sun breaks on Saturday but less sun on Sunday. Snow levels will crash down to below 1,500 feet by Sunday, and while precipitation will begin to taper in the lowlands, it will continue to snow heavily in spots in the mountains where a Puget Sound Convergence Zone focuses snowfall.

Sunday, a weak weather system brings some lowland rain and mountain snow once again, but amounts won’t be too heavy.

By Sunday evening, some snowflakes could be seen on higher hills and in the foothills, but generally the snow levels Sunday will be above 750 to 1,000 feet.

Monday through much of next week, snow levels will be below 1,000 feet at times, particularly in the overnight and morning hours.

Some lingering moisture is possible, so spotty areas of rain, a rain/snow mix or snow are possible at just about any time during these days — even in the lowlands.

Right now, it is impossible to pinpoint any chances for greater snowfall than flurries, owing to the lack of moisture expected and general uncertainty outside of the three- to five-day time frame.

Once we get through Friday’s storm, we ought to have a little better of a picture about next week’s very chilly weather pattern.