Rapid-fire storms with rain, snow and wind to hammer northwestern US during mid-December
By Alex Sosnowski, AccuWeather senior meteorologist
December 14, 2018, 11:36:58 PM EST
A series of storms will train across the northwestern United States and British Columbia into next week with periods of heavy rain, fog, mountain snow and gusty winds.
While a stormy pattern of this nature can occur a few times during a typical winter, there will still be some negative impacts with the greatest being on travel.
While a continuous fire hose effect is not forecast, the extent and magnitude of impacts are likely to increase as saturation occurs through progressively deeper layers of the ground and snow piles up over the high country from each storm.
The storms will arrive approximately every 24 to 36 hours through next Thursday.
Enough rain can fall with each storm to cause urban and small stream flooding, especially along the Interstate 5 corridor to the western slopes of the Cascades, over the Olympic Peninsula and Vancouver Island.
There is also the potential for mudslides and other debris flows.
Through next Thursday, there is the potential for 15-20 inches (380-500 mm) of rain in parts of western Washington and British Columbia with 5-10 inches of rain for parts of western Oregon and 3-5 inches of rain in coastal Northern California.
"Since freezing levels will generally be higher with most of the storms, when compared to the storm from Dec. 10-12, most of the heavy snow will fall above pass levels through next week in the northwestern U.S. and in southern British Columbia," according to AccuWeather Senior Meteorologist Dan Pydynowski.
"There will still be a couple of occasions where it snows and causes wintry driving over the passes as snow levels will tend to fluctuate with each storm and over the course of the storm train," Pydynowski said.
Heavy snow will generally be restricted to elevations above 5,000 feet during the pattern, with some variation.
The threat for heavy snow at higher elevations has resulted in a high risk for avalanches in the western slopes of the Cascades.
One of the bigger and stronger storms in the train may hit from Sunday to Sunday night.
Download the free AccuWeather app for the timing and duration of the rain as well as when snow may reach the passes.
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The storm train will translate to yards (meters) of snow for ski country and will help to ease long-term dryness and drought in eastern Washington, western and northern Oregon, northern Idaho and in part of Northern California, even though the Cascades and Coast Mountains will filter out a great deal of the moisture.
The fluctuating freezing levels, gusty winds and snowdrifts over the ridges will raise the risk of avalanches over the high country as the pattern continues.
Some rain and ridge-top snow will reach areas such as Spokane, Washington; Pendleton, Oregon; and Redding, California.
Accompanying the storms will be periods of gusty winds that will be most prominent along the coast and through the passes. Gusts from each storm, on average, will range from 40-50 mph, but they are likely to be locally higher with any storm. One or two storms during the pattern could hit with gusts of 50-70 mph.
The combination of periodic heavy rain, gusty winds and episodes of fog will lead to slow commutes for motorists. Expect airline delays as the storms affect the airports in the region, especially Seattle-Tacoma International Airport, Washington, and Vancouver International Airport, British Columbia.
Most of the rain and high-country snow will stay well north of San Francisco and Sacramento, California. However, there may be a brief episode of moisture that moves quickly through during the pattern and could dampen these areas and in part of Southern California.
The storm toward the end of this weekend may have the best chance of pushing rain and mountain snow into part of Southern California.
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