Another vigorous storm to dump more rain, mountain snow on Pacific Northwest

By Kyle Elliott, AccuWeather meteorologist
December 11, 2018, 11:29:42 PM EST

Following Sunday’s rainy, damp and chilly weather in the Pacific Northwest, an even stronger storm system will bring heavy rain and copious mountain snow to the region through Tuesday night.

Although residents in Seattle and Portland, Oregon, experienced an abnormally dry first week of December, the monthly rainfall deficits will be effectively erased this week.

The storm system that arrived Tuesday morning will continue to push inland over the northern Rockies through Wednesday.

The worst conditions in the coastal areas of the Northwest will continue through Tuesday night.

Static NW Into Tuesday Night

Not only will rain soak the Interstate-5 corridor from Seattle to Portland and snow bury the Cascades, but winds may also be strong enough to cause localized tree damage and power outages.

“Wind gusts of 40 mph are likely in the entire I-5 corridor from Portland to Salem and Seattle, with gusts up to 45 mph at the coast,” AccuWeather Senior Meteorologist Dave Houk said.

Rainfall amounts of 1 to 2 inches will be likely in Seattle and Portland, with up to 3 or 4 inches possible near the Washington coast.

Because severe to extreme drought is gripping a large portion of Oregon, according to the latest United States Drought Monitor, the rain will come as a welcome sight and help to fill up reservoirs across the state.

However, stream and river flooding concerns will ramp up farther north across western parts of Washington, where rainfall amounts are forecast to be highest.

At the very least, motorists will face treacherous travel conditions and have to contend with standing water on interstates and secondary roadways.

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While rain dampens coastal areas, a healthy dose of snow is expected to fall in the Cascades and northern Rockies through Wednesday.

The current snowpack in the Washington Cascades is well below normal for this time of year, according to the U.S. Department of Agriculture Natural Resources Conservation Service.

“While the snowfall will be good news for winter sports enthusiasts and ski resorts, it can create travel difficulties over the mountain passes,” AccuWeather Meteorologist Renee Duff said.

Around a foot of snow is forecast to bury I-90’s Snoqualmie Pass, and a slick covering of snow can even fall on I-5’s Siskiyou Summit in Oregon by Tuesday night.

Motorists should be sure to reduce speed when traveling in heavy snow or on snow-covered roadways in order to reduce the risk of spinouts and accidents. Motorists should check with state highway departments for vehicle restrictions when venturing over the passes.

Download the free AccuWeather app to find out how much rain or snow is expected this week in your location.

Farther inland, strong winds are forecast to occur along the eastern slopes of the northern and central Rockies, associated in part with this storm as a Chinook wind event unfolds.

"Gusts to 80 mph are possible from western and central Montana to north central Colorado, beginning Tuesday night and lasting to Wednesday night in some locations," according to AccuWeather Senior Meteorologist Alex Sosnowski.

"Gusts this high pose a danger to motorists and may cause property damage," Sosnowski said.

Residents of the Northwest will barely have time to catch their breaths behind this system before the next storm comes ashore Wednesday night into Thursday.

NW regional 12.12 PM

In fact, the stormy pattern is expected to persist through the weekend and into next week as additional storm systems target the Northwest on an every-other-day basis.

"There seems to be at least five or six storms lined up, like a train, set to slam into the Northwest through the middle of next week," Sosnowski said.

"While this many storms in that short of time are not unusual for the region, they can still pack a punch and have significant negative impact on travel, commerce and shipping in the region prior to Christmas."

As much as 12 inches of rain and over 4 feet of snow may fall in the hardiest-hit locations by the middle of next week with the stormy weather pattern showing no signs of ending in the near future.

That type of rain and snowfall can lead to flash flooding and mudslides, as well as raise the risk of avalanches over time.

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