US: Adverse winter weather forecast across northwestern regions through at least Jan. 4

Adverse winter weather is forecast across parts of the northwestern US through at least Jan. 4. A Pacific system will bring another round of locally heavy coastal rains and higher elevation snow to the northwestern US and Rockies through Jan. 4. Ongoing coastal rain, a lower elevation mix of rain and snow, and higher elevation snow will begin to ramp back up late Jan. 2 as another system moves into the Pacific Northwest, bringing additional moisture to the coast and inland. Heavy rainfall is likely for upslope regions along the coastal ranges of southwestern Oregon and northern California and inland along the Sierra in northern California through Jan. 3. Some isolated instances of flooding will be possible. Heavy, accumulating snowfall is expected in the Cascades and Sierra and the northern Rockies Jan. 3 before spreading into the central Rockies Jan. 4 as the system continues inland. Snowfall totals of more than 0.3 meters (1 foot) are likely for the higher mountain peaks. A mix of light to moderate rain and some snow will pass inland through the Great Basin Jan. 3, with little to no accumulations expected.

As of late Jan. 2, the National Weather Service (NWS) has issued winter storm warnings across northeastern California and northern Montana. Winter weather advisories are in effect across most of the rest of the affected area. Officials could update and extend the coverage of the weather alerts over the coming days.

Snow accumulations are likely across the affected region, especially at higher elevations. Lesser accumulations are possible where sleet and freezing rain mix with the snow, and precipitation is less intense. In addition to the heavy snow, strong wind gusts will likely lead to periods of blowing and drifting snow in some areas. Sporadic power outages could occur throughout the affected region.

The winter weather will likely disrupt ground and air transport across the region. Traffic and commercial trucking delays are probable along regional highways. Dangerous and challenging driving conditions are likely on secondary and rural roads in the affected states as maintenance crews prioritize clearing major routes. Authorities will probably close stretches of highways if driving conditions become too hazardous. Flight delays and cancellations are likely due to ground stops and deicing operations at regional airports.