Oregon is defined by its geographic and climatic contrasts, meaning whether it snows in December depends entirely on the specific location and elevation. The state is broadly divided into climate zones, with the towering Cascade Range serving as a distinct barrier. This barrier separates the mild, wet conditions of the west from the cold, arid environment of the east, ensuring a wide variety of winter weather.
Snowfall Patterns in Western Oregon Lowlands
The majority of Oregon’s population resides in the low-elevation regions west of the Cascade Mountains, including the Willamette Valley and the immediate Coast. The influence of the Pacific Ocean creates a maritime climate that keeps winter temperatures relatively mild. This moderating effect means that most December precipitation falls as rain, often accompanied by cold, persistent fog in the valleys. The average December snowfall in the Willamette Valley, including major cities like Portland and Salem, is typically a light dusting, averaging around 1.4 inches. When snow does occur, it usually results from a specific weather pattern that pulls cold air from the interior, and the snow generally melts quickly.
Reliable Snow in the Cascade Range
The Cascade Range is the definitive location for reliable December snowfall, with high elevations acting as a massive sponge for Pacific moisture. Above approximately 4,500 feet, the ground is consistently covered with snow starting in early December, establishing a deep snowpack that lasts well into spring. This elevation receives the heavy, wet snow crucial for winter recreation. December accumulation is significant; areas like Government Camp near Mount Hood record a monthly average of over 51 inches of new snow. High-altitude sites such as Crater Lake Park average over 90 inches in December, providing the snowpack that feeds major ski resorts and serves as a vital water reservoir.
High Desert and Eastern Oregon Climate
East of the Cascade crest, the climate shifts into the high desert and arid plateau environment. While this area is colder than the Willamette Valley, its December snowfall is often lighter and drier due to the rain shadow cast by the Cascades, which blocks much of the Pacific moisture. For example, Bend in Central Oregon sees an average of about 5.3 inches of snow in December. Temperatures in this region are much colder, often dropping into the low 20s or teens. These lower temperatures lead to frequent deep freezes, making the snow that does fall lighter and more powdery.
Navigating Oregon Mountain Passes in December
Travelers planning to cross the mountains in December must be prepared for winter driving, as the high-elevation passes are guaranteed to have snow and ice. The Oregon Department of Transportation (ODOT) frequently implements chain requirements on major routes, including Interstate 5 over the Siskiyou Summit and highways like US 20 (Santiam Pass) and US 26 (Government Camp). These regulations are legally binding and enforced. All vehicles are required to carry traction tires or tire chains when traveling through designated mountain pass zones. For most passenger vehicles, traction tires may be used in lieu of chains under typical conditions, but chains must still be carried. Before any journey, checking the ODOT TripCheck website is necessary to determine the current road conditions and specific chain requirements.