Atmospheric river could bring 300 mm of rain, potential flooding to parts of BC

Weather officials are warning residents in British Columbia's South Coast region of another atmospheric river system that could bring storms and elevate flood risks starting Saturday.

Environment and Climate Change Canada says the region is expected to see periods of heavy rain combined with melting mountain snow until Wednesday.

It warns there is an elevated risk of flooding, high river levels and landslides in a zone covering Vancouver, Squamish and the Sunshine Coast as well as the Vancouver Island communities of Nanaimo, Port Alberni, Tofino and Campbell River.

Forecasts call for up to 300 millimetres of rain over five days, with the Howe Sound area expecting as much as 250 mm while Inland Vancouver Island and parts of the Fraser Valley could receive 150 mm and 120 mm respectively.

BC's Ministry of Emergency Management and Climate Readiness says in a release that the storms may also bring winds that could cause power outages, and the province's River Forecast Centre is monitoring streamflow closely.

The centre has placed all of Vancouver Island, the Howe Sound region, the Sunshine Coast and parts of Metro Vancouver and the Fraser Valley under a flood watch, with high streamflow advisories extending east into the Fraser Canyon and north into the central coast.

The narrow bands of heavy precipitation are known as an atmospheric river, which occur frequently in the fall and winter in BC.

One such event in November 2021 led to massive flooding and mudslides that knocked out major road and rail corridors throughout the province, snarling supply chains and triggering gasoline rationing in the Lower Mainland.