A massive winter storm is sweeping across the western United States, bringing dangerous snowfall, powerful winds, and treacherous travel conditions to parts of Washington, Oregon, Montana, and Wyoming this week.

The four states are under multiple winter weather advisories through Friday (March 13), with some mountain regions expected to see two to four feet of snow and wind gusts reaching up to 55 mph. Officials are urging drivers to delay all travel if at all possible.

The National Weather Service (NWS) warns that "significant snowfall with periods of heavy snowfall rates will combine with low visibility to create difficult driving conditions." In some mountain passes, conditions could become "difficult to impossible" for drivers.

The hardest-hit area is expected to be the Washington Cascades, where a winter storm watch is in effect from late Tuesday (March 10) night through Friday (March 13) morning. The upper slopes of the eastern Cascades crest — including areas near Easton and Roslyn — could see eight to 14 inches of snow through Tuesday (March 10), with wind gusts up to 40 mph. Later in the week, snowfall totals could climb dramatically, with two to four feet possible in the mountains.

In the south Washington Cascades, including areas near Mount St. Helens, forecasters expect six to ten inches of snow through Tuesday (March 10), along with gusts up to 35 mph, with another round of heavier snow possible as the storm strengthens.

Oregon is also in the storm's path. The north Oregon Cascades — including Government Camp and areas near Lost Lake and Timothy Lake — are forecast to receive four to ten inches of snow between Monday (March 9) morning and Tuesday (March 10) evening, with wind gusts up to 40 mph. Officials warn that bridges and overpasses are especially prone to dangerous icing.

Further east, parts of Montana and Wyoming are also under winter weather advisories. In southern Big Horn County in Montana and the Sheridan foothills of Wyoming, one to three inches of snow are expected, with up to five inches possible in higher terrain through Wednesday (March 11) morning. The nearby Bighorn Mountains could see four to eight inches of snow, and winds may gust up to 30 mph, making travel difficult along US Highway 14.

Weather officials note that even modest snowfall can turn roads deadly as temperatures drop and surfaces ice over quickly. Drivers in affected areas are urged to slow down and exercise caution. Those crossing mountain passes should carry emergency winter kits, including blankets, water, food, flashlights, and tire chains.

Forecasters say the storm system is expected to intensify later this week in the Pacific Northwest, raising the possibility of additional heavy snowfall in the Cascades and continued dangerous travel conditions across the region through at least Friday (March 13).