Southern B.C. braces for heavy rain as atmospheric river makes landfall

An atmospheric river has made landfall in southern British Columbia, prompting Environment and Climate Change Canada to issue rainfall warnings for Metro Vancouver and Vancouver Island.

The storm is expected to deliver up to 150 millimetres of rain over parts of Vancouver Island while Vancouver and the Fraser Valley are forecast to see between 50 and 100 millimetres Monday.

The weather service says the rain will turn to snow at higher elevations before easing Tuesday morning.

Environment Canada is warning drivers on the Sea to Sky Highway from Squamish to Whistler, and the Coquihalla Highway from Hope to Merritt, to be cautious due to heavy rains and potential snow raising the risk of flooding and landslides along the routes.

While the storm is expected to be weaker than the series of atmospheric rivers that caused massive flooding and landslides that killed five people in November 2021, the precipitation could bring localized flooding, landslides and washouts near rivers and creeks, Environment Canada warned.

To mitigate flood damage, the province deployed sandbags to 27 local governments, including Indigenous communities, according to a statement from B.C.'s emergency management ministry.

Up to four million sandbags and 32 kilometres of tiger dams could be deployed to protect homes and public buildings, if required, the statement said.

Residents are advised to clear perimeter drains and gutters of debris and move possessions from low-lying areas to higher ground to prevent flood damage.

The B.C. River Forecast Centre initially issued a high streamflow advisory for the South Coast, indicating river levels are expected to rise rapidly, and upgraded that to a flood watch Monday morning. 

The atmospheric river combined with the recent snow pack and warm temperatures is cause for concern as it could contribute to unpredictable water level changes, according to the notice.

Jonathan Boyd, a hydrologist with the centre, says localized flooding could occur but catastrophic flooding is unlikely.

“The atmospheric river is there but it doesn’t seem to be as intense, not as long lasting, as the one from November 2021. The other major difference is that it was very wet the two months leading up to the flood events,” said Boyd.

Boyd went on to say that this past summer, and parts of September and October, were dry and the most recent significant rainfall hit the region nearly a month ago.

“That’s working in our favour in the sense the river systems are low and not necessarily at a high level and the ground's less saturated than it was in November 2021.” 

The atmospheric river also triggered a winter storm warning for the B.C. Interior, with up to 25 centimetres of snow forecast for Yoho National Park, Rogers Pass and Eagle Pass.

Farther south the snow is expected to turn to rain with between 75 and 100 millimetres projected to fall in the southeastern Kootenay region through to Thursday morning.