How an atmospheric river flooded British Columbia and led to floods and landslides

Canada’s west coast is known for its rainy fall weather, but the storm recently experienced by the Fraser Valley in British Columbia was one of the record holders.

A meteorological system called the “atmospheric river” flowed through the southwestern corner of the province and over two days caused strong winds and nearly record rainfall, causing massive flooding and landslides.

Hope, Merritt and Princeton, which were particularly hard hit, received 100-200 millimeters (or more) of rainfall. And all highways connecting Vancouver to the rest of the province have been closed due to wash-downs and landslides, isolating the city from the rest of Canada, at least along the road, with significant economic impact.

An atmospheric river is a strip of warm, moist air hundreds of kilometers long and hundreds of kilometers wide, bordered by a large cyclonic system of low pressure.

The term was applied to bands of moisture-related weather systems that move inland from the Pacific Ocean. The atmospheric river can reach the coast anywhere between southeast Alaska and Northern California.

Due to the large amount of moisture carried by these weather systems, the term has become a metaphor for a land river. However, atmospheric rivers are not carried along the canal like a real river, and colossal amounts of rain can fall over large areas.