Canada, US: Severe weather forecast to continue across parts of southwestern Canada and the northwestern and western US through at least Nov. 24 /update 1

Severe weather is forecast to continue over parts of southwestern Canada and the northwestern and western US through at least Nov. 24. A second powerful storm system in less than a week is expected to move into the region from the Pacific Nov. 22-23, bringing rainfall to coastal areas, strong winds across the region, and snowfall over elevated parts of the southwestern and western British Columbia in Canada and the Pacific Northwest in the US. The previous storm that impacted the region Nov. 19-20 brought widespread power outages affecting hundreds of thousands of people and some disruption to air, ground, and maritime transport; similar disruptions are likely during the passing of the coming storm system. Further south, an associated atmospheric river is expected to continue to bring extremely heavy downpours to northern California, as well as heavy snowfall to areas further inland. Winds gusting up to 110 kph (68 mph) are possible in exposed coastal areas of British Columbia, snowfall accumulations of more than 30 cm (12 inches) are possible in elevated areas of northern and east-central California, and rainfall totals of up to 25 cm (10 inches) are possible in parts of northern California. Flooding is likely in areas where sustained 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. 22, Environment Canada has issued red snowfall warnings (the highest level on a three-tier scale) for parts of south-central British Columbia and red wind and grey special weather statements for strong winds for southwestern and western parts of British Columbia.

The US National Weather Service (NWS) has issued flood warnings, watches, and advisories across parts of northern California and southwestern Oregon. Winter storm warnings are in place across parts of eastern and northeastern California and high wind warnings and advisories have been issued across parts of northern California and the Pacific Northwest. Storm, gale, and hazardous sea warnings and high surf advisories 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. 22 and a moderate risk of excessive rainfall for surrounding areas of northern California and into far southwestern Oregon Nov. 22 and isolated pockets of northern California late Nov. 22-23. There is a slight risk of excessive rainfall for other surrounding areas of northern California and far southwestern Oregon Nov. 22-23.

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

The storm system could produce further 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.