Potentially Crippling Snowstorm for Seattle, Portland

Major snowstorms have missed most major cities in the U.S. so far this winter, but a gathering storm is about to plaster the Pacific Northwest, including cities that don't normally see much snow, including the Seattle and Portland metro areas. Forecasts for Seattle call for up to a foot or more of snow to fall during the next few days. The heaviest snow is expected to fall Tuesday night through Wednesday, with more snow possible later this week. 

Computer model snowfall forecast for the Seattle area, ending early Thursday. Credit: Cliff Mass weather blog.

Considering that Seattle typically sees just 5.9 inches of snow during an entire winter, this storm is likely to cause major problems for the city. According to the National Weather Service, snow amounts at Sea-Tac airport could surpass anything seen since November 1985. Forecasters are trying to determine if/when the snow will change to rain at lower elevations, which would affect snowfall amounts. This is especially likely to take place in Portland, Ore., and other areas south of Seattle, but depending on the track of the storm, precipitation could remain all snow in Seattle.

Here's University of Washington weather blogger Cliff Mass' take on the situation on Monday:

“Cutting to the chase, Seattle may well get 6+ inches of snow during the next two days. SW Washington could get more. The mountains, particularly the central Cascades southward could get feet—like 3-4 feet.  In short, one of the biggest events we have had in years…

There has been some hype about this event…it is NOT going to be as bad as December 1996.  I remember that well.  We had two snowstorm the last week in December and I had 21.5 inches on the ground at my house.  Then it got very warm and windy and heavy rain rapidly melted the snow.  Just a disaster, with collapsed roofs and slope failures.”

Mass posted an update today that downgraded the snowfall forecast for Seattle to between 2-5 inches, but noted that a shift in the storm track would push that back up. 

“Folks this is a very difficult forecast.  Everything depends on getting the track of the low exactly right…first to decide where the rain/snow changeover will be and secondly to get the amount of precipitation right.”

Computer model forecast showing a plume of Pacific moisture aimed at the Pacific Northwest, fueling the developing winter storm. Credit: Cliff Mass weather blog.

Even more snow — to be measured in feet — will pile up in the Cascades and Bitterroots mountains, and the snow will eventually roll eastward into Montana, Idaho, and Wyoming. The longer-term weather pattern looks wetter for northern California, which is good news, since much of the state has been experiencing an extraordinarily dry start to 2012.

Track the storm: 

National Weather Service Seattle
liff Mass' Weather blog
ING 5 TV (Seattle)
National Weather Service Portland, Ore.
KATU TV (Portland, Ore.)
KGW TV (Portland, Ore.)