Series of Storms to Bring Snow, Ice, Rain and Wind to Northwest

December 2,2015

An active weather pattern continues into December as multiple rounds of snow, ice, rain and wind are targeting much of the Northwest.
A number of different watches, warnings and advisories have been issued by NOAA's National Weather Service (NWS) across the region for the snow, ice and wind impacts that are expected from the stormy weather, stretching from Washington to northern California.
(MORE: 1 Million Lose Power in Destructive Northwest Storm)

Winter Weather Alerts

Through 12 p.m. PST Thursday, the NWS has posted a freezing rain advisory for parts of the Columbia River Gorge, Hood River Valley, as well as locations below 2,500 feet along the southern Washington Cascades. New ice accumulations of 1/10 to 1/4 of an inch are possible into Thursday.
(MORE: What Ice Accumulation Means)
Across parts of interior Washington and Oregon, winter weather advisories and winter storm warnings have been issued, for a combination of light to moderate snow and ice over the next few days.
(Forecast: Medford | Portland | Seattle)
In addition to the winter weather alerts, high wind warnings have been issued for portions of coastal and southern Oregon. Wind gusts as high as 70 to 90 mph are expected in some of these areas, particularly on the coast, through Thursday. High wind warnings and wind advisories are in effect for coastal northwest Oregon and coastal Washington for strong winds into Thursday.

First Storm Arrived Tuesday Night-Early Wednesday

The first in the series of impactful weather systems arrived in the region Tuesday night into early Wednesday.
Freezing rain accumulations of a half inch thick were reported near Skamania, Washington. In Oregon, Troutdale saw ice accumulations of up to one quarter inch thick.
Ice and snow in eastern Oregon from the storm forced school cancellations in Hermiston, Pendleton, Umatilla, Boardman, Milton-Freewater and elsewhere, The Associated Press reported. Icy roads in the Columbia River Gorge also closed or delayed schools on both sides of the Oregon-Washington line.

Next Storm Brings High Winds, Ice, Rain and Snow Through Thursday

Forecast Winds Thursday

A sharpening pressure gradient ahead of the next storm system will bring strong winds to much of the region on Thursday.
While widespread wind gusts over 30 mph can be expected from the Pacific Northwest to northern Rockies, favored terrain may experience much higher winds. Gusts to 70 mph may impact much of the Cascades, while winds could reach 90 mph in gusts along the southern coast of Oregon. Portions of northwest Oregon and western Washington could see gusts up to 65.
As of Wednesday night, power outages had already been reported due to high winds on Snoqualmie Ridge.

Thursday's Forecast

In addition to the winds, some ice and snow will persist across interior parts of Oregon and Washington. Across northern California, some much needed precipitation, falling in the form of rain across the lower elevations, is likely. Snow will move into the northern Sierra Nevada Thursday afternoon into early Friday. A winter storm warning has been issued by the NWS for parts of the northern Sierra, where snowfall rates of 1-2 inches per hour could impact Donner Pass on I-80.

Heavier Rain Possible Over the Weekend

Although conditions should gradually improve on Friday with just a bit of light precipitation across the Northwest, the next round of active weather may return as soon as Saturday.
The current thinking is that some locally heavy rain may reach western Washington and the coast of Oregon on Saturday. Some lighter precipitation may reach in the mountains in the form of snow.
Precipitation could continue into Sunday, although the heaviest of rain is expected to fall early in the weekend. Even more rain may move into parts of the Northwest early next week as the stormy pattern continues.

Forecast Rain and Snow Through Sunday

When all is said and done, a swath of 3 to 5 inches of rain is possible from the northern coast of California, to the Oregon coast and much of western Washington.
Locally heavier rainfall totals will be possible along the immediate coast and in higher elevations.

Unsettled Atmospheric Setup

An active pattern is likely to prevail through the first week of December, especially once a stubborn cutoff area of low pressure over the central U.S. ejects eastward through Thursday.
That cutoff low, which spawned both Winter Storm Cara and Winter Storm Delphi, has led to a stagnant weather pattern across the Northwest in recent days.
Now that it's moving out, several ripples of energy in the upper atmosphere will be able to dive from the northeastern Pacific Ocean across the Northwest and pivot through the region relatively quickly.

A look at the upper level pattern across the northern Pacific Ocean and western North America.

As often is the case with storm systems in the region, particularly in the cool season, this means strong winds and locally heavy precipitation favor coastal areas. While some snow is still expected across the mountains, precipitation totals will be fairly limited due to the speed of the storm systems, ultimately limiting the snowfall potential.
The jet stream pattern may support more storminess into next week, but it is far too early to get into specifics.
For the latest information on this complex setup, regularly check back to weather.com for updates.
MORE: Northwest Powerful Wind Storm, Nov. 18, 2015