US: Adverse winter weather forecast across northwestern regions through at least Dec. 28

Adverse winter weather is forecast across parts of the northwestern US through at least Dec. 28. Multiple weather systems are forecast to pass over the region, bringing rounds of moderate to heavy lower elevation and coastal rain, an inland lower elevation mix of rain and snow, and very heavy snow to the mountain ranges. Around 7.5-13 cm (3-5 inches) of rain is likely along favorable upslope regions of the coastal ranges of the Pacific Northwest and northern California through Dec. 27, with the potential for some isolated flooding. In the mountains, storm total snowfall of at least 20-30.5 cm (8-12 inches) will be common, with locally higher amounts of more than 0.6 meters (2 feet) possible, especially for the Cascades and ranges of the northern Great Basin and the Rockies. In addition, strong and gusty winds are also expected. Hazardous travel conditions are likely due to reduced visibility caused by blowing snow.

As of late Dec. 25, the National Weather Service (NWS) has issued winter storm warnings across parts of southern and central Idaho, northern and central Utah, northern, western, and central Washington, and far western Wyoming. Winter weather advisories are in effect across 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.