Canada, US: Severe weather forecast across parts of southwestern Canada and the northwestern and western US through at least early Nov. 23

Severe weather is forecast over parts of southwestern Canada and the northwestern and western US through at least early Nov. 23. A powerful storm system is expected to move into the region from the Pacific over the coming days, bringing rainfall to coastal areas, strong winds across the region, and snowfall over elevated parts of the affected area Nov. 19-20. An associated front is then expected to bring extremely heavy downpours to northern California Nov. 20-23. The main threat from the storm in Canada is expected to be strong winds, with winds gusting up to 120 kph (75 mph) possible around the Pacific coast in British Columbia. Strong winds are also expected in the northwestern and western US, as well as heavy mountain snow over the Pacific Northwest and increasingly heavy rainfall over northern California. Flooding is possible in areas where heavy rainfall occurs and hazardous travel conditions are likely in areas where more wintry precipitation falls due to slippery roads and reduced visibility caused by blowing snow. Strong winds may cause property damage and power outages.

As of early Nov. 19, Environment Canada has issued red heavy rainfall warnings (the highest level on a three-tier scale) and grey special weather statements for strong winds across parts of southwestern and western British Columbia.

The US National Weather Service (NWS) has issued blizzard warnings for parts of central and northern Washington and winter storm warnings for parts of central and northern Washington, southern Oregon, and northern California. Winter weather advisories are in place for parts of eastern, southern, and western Washington, far northern Idaho, central and northern Oregon, and northeastern California. High wind warnings and advisories are in place across much of the affected area and flood watches, avalanche warnings, and freeze warnings are in place across parts of northern and north-central California. Hurricane-force wind, storm, and gale warnings are in place for coastal waters off the northwestern and western coast.

The NWS's Weather Prediction Center has forecast a high risk of excessive rainfall (the highest level on a four-tier scale) across parts of northwestern California Nov. 21-22 and a moderate risk of excessive rainfall for surrounding areas of northwestern California and into far southwestern Oregon Nov. 20-22. There is a slight risk of excessive rainfall for other parts of northern and northwestern California and far southwestern Oregon Nov. 19-23.

Officials could update and extend the coverage of weather alerts over the coming hours.

The storm system could produce rounds of heavy precipitation, including rain and snow, and strong winds across the affected area. Where precipitation falls as rain, flash, and areal flooding is possible. Such flooding is possible in low-lying communities near watercourses and other large bodies of water, as well as in urban areas with easily overwhelmed stormwater drainage systems. Sites located downstream of large reservoirs may be subject to flash flooding after relatively short periods of intense rainfall. Precipitation could fall as snow in elevated parts of the affected area over the coming days. Wind gusts could cause blowing and drifting snow; decreased visibility is likely in these areas.

Floodwaters and related debris may render some bridges, rail networks, or roadways impassable, impacting overland travel in and around the affected area. Flooding in urban areas could also result in significant traffic congestion. Heavy snow will likely make driving hazardous in mountainous areas; authorities could implement temporary road closures or detours in such locations.

The disruptive weather will likely cause some delays and cancellations at airports in the region. Flooding or snow could block regional rail lines; freight and passenger train delays and cancellations are possible in areas that see heavy rainfall and potential track blockages.

Disruptions triggered by inclement weather and resultant hazards, such as flooding or strong winds, could persist well after conditions have improved - it could take days before any floodwaters recede and/or officials clear debris. If there is severe damage to infrastructure, repair or reconstruction efforts may result in residual disruptions.