SEATTLE - The coldest storm system of this fall season will be working across the Pacific Northwest beginning Wednesday night and lasting through the day Thursday.  It promises cold rain through the lowlands, and rain changing to snow in the high country.

The storm isn't particularly potent or moisture-laden, but it is a cold system, with temperatures aloft cooling to well below freezing.  

Showers will begin at the coast and through the Olympics Wednesday afternoon and evening, with showers across the Puget Sound lowlands by Wednesday night.  Showers will persist through Thursday with high temperatures not getting out of the 40s for Seattle, Tacoma, Everett and the rest of the metro area.

Snow likely at Snoqualmie & Stevens Passes, Unlikely To Cause Major Travel Troubles

Since the storm is not extremely strong or rich in Pacific moisture, the amount of snow will not be terribly significant for the passes.  Expect 1-3 inches of snow at Snoqualmie Pass by early Thursday with 2-4 inches at Stevens Pass possible by then.  Light snows will then continue off-and-on through Thursday adding another inch of accumulation.

Flurries or light snow showers in the mountains will persist into the weekend and likely even next week as Western Washington gets stuck in a cold pattern.

Forecast snow levels:

• Wednesday night: 3,500 feet falling to 2,500 feet by Thursday morning
• Thursday-Thursday night: 2,500 feet 
• Friday-Friday night: 1,500-2,000 feet
• Saturday-Monday: 2,500 feet

Since heavy snowfall isn't expected, travel through the passes shouldn't be treacherous.  However, less-traveled roads in the mountains could be icy, especially at or below pass levels where thawing and re-freezing is possible.

Heavier Snowfalls For Higher Elevations And Ski Resorts

Snowfall will be heavier above 5,000 feet through Friday morning, and areas around Paradise and Mount Baker could see snow totals in the six to ten inch range through the end of the week.   A Winter Storm Watch has been issued for the north Cascades, including Mount Baker. 

Ski resorts will also begin picking up good snow amounts toward the summits.

Lowland Rainfall Signals Beginning of "Wettest Month of the Year"

November is, on average, the wettest month of the year for Seattle and the rest of the Western Washington lowlands.  

Rainfall during the month of October was just about on par with average, with Sea-Tac Airport receiving 3.45 inches with a normal of 3.48 inches.  That is significantly drier than last October's 5.24 inches.

While the fall hasn't started off terribly wet, the pattern we're about to enter in November favors significantly higher rainfall.  Normally, we receive just shy of six inches of rainfall in a given November in Seattle, and I would be surprised if we did not equal or exceed that value this month.

Rivers across Western Washington aren't particularly high, as is expected following a fairly typical October, but can rise quickly.   You can keep track of river levels through the season using the National Weather Service's AHPS system.  And, of course, we'll be tracking any river flood events extensively on KIRO 7 and at kirotv.com