Pacific Northwest preparing for heavy rain and snowfall as December storms approach

The northwestern United States and southern British Columbia are entering a period of intensified winter weather as a series of storms is set to arrive. While the storm at the end of this week will only provide a preview, meteorologists warn that December could bring substantial flooding, mudslides, and avalanches.

"A modest atmospheric river is expected to accompany the system from Thursday night into Friday," said Brett Anderson, Senior Meteorologist at AccuWeather.

Snow levels are projected to remain mostly above the main mountain passes in the Cascades through early next week, according to Anderson. As the storm moves in on Friday, snow is likely to increase in the Cascades, while inland areas at higher elevations may experience icy conditions and localized snow.

Rain along the coasts of British Columbia, Washington, and northern and central Oregon through Friday is expected to raise the risk of urban flooding, water pooling on roads, and rapid rises in smaller streams.

The storm is anticipated to continue inland, producing significant snowfall from Montana to the northern and central Plains over the weekend, affecting many areas that recently experienced heavy snow. Another system is forecast to arrive by the weekend, bringing additional rain to lower elevations and mixed wintry precipitation across the Washington Cascades.

Pacific Northwest Faces Series of High-Impact Storms

The stormy conditions are expected to persist beyond this weekend. A new storm is projected to move onshore every one to two days next week, potentially causing travel disruptions and impacting daily life across the region.

A system arriving Monday into Tuesday may bring a strong atmospheric river, which could result in heavy rainfall and elevated flooding risk across western Washington and Oregon, according to Kyle Lavery, Storm Warning Meteorologist at AccuWeather.

Later in the week, another storm could signal a broader pattern change, moving southward from the Gulf of Alaska along the coasts of British Columbia, Washington, and Oregon. This may lower snow levels in the Cascades, allowing accumulation at mid-elevations and surrounding hills.

"Between December 12-16, a series of powerful systems could impact the Northwest coast, extending as far south as Northern California," said Joe Lundberg, Senior Long-Range Meteorologist at AccuWeather. "Some storms may even bring snow down to near sea level."

The Pacific Northwest is expected to receive unusually high moisture over the next two weeks, far exceeding historical averages. For example, Seattle normally sees about 5.72 inches of rain in December, but certain areas along the Interstate 5 corridor could receive double that amount. The west-facing slopes of the Olympics, Coast Ranges, and lower Cascades may accumulate 1-2 feet of rain by mid-December.

These conditions will significantly increase the likelihood of flash flooding and mudslides. Mountain regions could see several yards of snow in the high country, raising avalanche risks and contributing to potential flooding and mudslides as temperatures fluctuate.

Author: Olivia Parker