Weather Warning: Three atmospheric rivers for B.C. over the next week


Weather warnings are once again in effect for parts of Vancouver Island and the BC South Coast, due to a parade of potentially serious atmospheric rivers.

“Three atmospheric rivers within a week and at this point, the Saturday system does look very significant,” says Environment Canada and Climate Change warning preparedness meteorologist Geoff Coulson.

“The way it’s gone this fall is really adding insult to injury, not only the number of atmospheric rivers we’re dealing with but the potential amounts some of them could be giving.”

The first storm — Wednesday night into Thursday — could bring 100 to 150 mm of precipitation to the west coast of Vancouver Island and up to 100 mm to the North Island.

But the next atmospheric river, Saturday into Sunday, is expected to be even stronger, and Tuesdays could be even worse.

It’s the last thing the Island and province needs, after devastating flooding.

“This is a major concern, especially due to the vulnerabilities from the previous event,” says Jonathan Boyd, a hydrologist with the River Forecast Centre.

A high streamflow advisory has been issued for Vancouver Island and because these atmospheric rivers are the type known as a pineapple express, pulling in sub-tropical moisture, temperatures and freezing levels will rise.

“There’s the risk of rain on snow so you could see another potentially 20 to 80 mm of water equivalent going into the river systems, just from the melting of the snowpack,” Boyd says.

It’s been a record fall for rainfall. The last two months have been the rainiest period in the last 80 years in Greater Victoria with back-to-back and very intense atmospheric rivers.

“We’re talking about many of these atmospheric rivers with lengths of over 2,000 kilometres, widths of around 800-900 kilometres wide,” Coulson explains.

“And what’s most important is the depth of that atmosphere where that moisture is. Three to four kilometres of very moist air associated with these atmospheric rivers and that’s what gets realized as rain and snow.”

In case you were wondering, the term atmospheric river isn’t new — it was coined in the 90s to describe a long and narrow stream of water vapour in the atmosphere.

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