US, Canada: Adverse weather likely in Northwest, Northern Rockies and Plains, and West, US, and western and northern Canada through Dec. 23 /update 31

Event

Further snow, rain, and possible flooding are likely in parts of the Northwest, Northern Rockies and Plains, and West regions in the US and western and northern Canada through at least Dec. 20. Lingering disruptions are also ongoing in British Columbia, Canada, following severe flooding.

Authorities in British Columbia have extended the provincewide state of emergency through Dec. 28 as recovery efforts are still underway. Officials closed multiple roads and railways throughout the province, including major routes to and from Vancouver, since Nov. 15 due to flooding; most roads have reopened. Additional rainfall could result in flooding or flash flooding on already saturated soil and exacerbate current disruptions.

Government Advisories
A "High Risk" for heavy snow of more than 10 cm (4 inches) is in place across portions of the western US and the Northern Plains through at least Dec. 23. At least 15 cm (6 inches) of snow is possible for the Washington Cascades eastward across northern Idaho into western Montana Dec. 20. An increased likelihood of the same level of snow is likely over the northern Washington Cascades and parts of northern California Dec. 21 and for the Washington Cascades and Olympics southwards along the Oregon Cascades and into northern California through the Sierra Nevada mountains Dec. 22. Snowfall of 15 cm (6 inches) is also likely across parts of northern and central Idaho Dec. 22.

As of early Dec. 20, the US National Weather Service has issued winter storm warnings for parts of central and southern Washington, northern Oregon, and western Montana. Winter weather advisories have been issued for parts of central and southeastern Washington, central, northern, and northeastern Oregon, central Idaho, western and central Montana, far northern Wyoming, and northern California. Avalanche warnings are in place for parts of northwestern Montana and winter storm watches are in place for parts of central California. Flood watches have been issued for parts of western Oregon and freezing fog advisories for parts of western Nevada.

The Meteorological Service of Canada has issued red (the highest level on a three-tier scale) Arctic Outflow warnings for parts of western British Columbia, and red snowfall and blizzard warnings for western parts of Northwest Territories. Blizzard, snowfall, wind, and winter storm warnings are also in place for parts of northern Nunavut. Officials could update and possibly extend the coverage of the relevant weather alerts over the coming days.

Hazardous Conditions
Snow accumulations are likely across the affected area. Lesser accumulations are possible where sleet and freezing rain mix with the snow, and precipitation are less intense. In addition to the heavy snow, strong wind gusts will likely lead to periods of blowing and drifting snow. Blizzard conditions are possible. Sporadic power outages are possible throughout the affected area.

Transport
Multiple sections of highways 1, 5, and 8 and many other roads in British Columbia remain closed due to heavy rain, landslides, and damage. Road reconstruction is underway, and authorities have estimated that Highway 1 will reopen mid-January, and Highway 5 is likely to be reopened early January. Authorities have not provided an estimation for the reopening of Highway 8. Authorities only permit essential travel on Highway 3 between Hope and Princeton and Highway 99 from Lillooet River Road to the BC Hydro Seton Lake campsite access in Lillooet.

Additional traffic and commercial trucking delays are possible along regional highways. Dangerous and challenging driving conditions are also likely on secondary and rural roads in the affected states as maintenance crews prioritize clearing major routes. Flight delays and cancellations are likely due to ground stops and deicing operations at regional airports.

Advice

Monitor local media for updated weather information. Verify road conditions before driving in areas where heavy snowfall is forecast. Allow extra time to reach destinations in these areas and carry an emergency kit and warm clothes if driving is necessary, especially on secondary or rural routes that could become impassable. Plan accordingly for delivery delays if routing shipments by truck through the affected area Confirm flights. Charge battery-powered devices in the case of prolonged electricity outages.

Resources

US National Weather Service
US Road Conditions
Meteorological Service of Canada
DriveBC