B.C.'s South Coast bracing for atmospheric river with up to 100 mm of rain possible

Environment Canada has issued another weather warning for the South Coast of British Columbia.

An atmospheric river event is expected to melt weeks' worth of snow at a rapid rate which could trigger localized flooding.

“Heavy rain will develop early this afternoon as the first system arrives and continue until Wednesday afternoon as additional systems impact the coast,” a warning posted by Environment Canada Tuesday morning said.

Most parts of Metro Vancouver and the Fraser Valley are expected to see 75 to 100 millimetres of rain.

“The heaviest hit areas of Metro Vancouver are going to be the North Shore mountains. That's where you could see easily 150 millimetres or even more of rain,” said Bobby Sekhon, of Environment Canada.

Sekhon says that amount of rain is significant when combined with melting snow and ice already on the ground.

“We can certainly get more moisture added to the river systems causing higher flows in the rivers and streams, but also overland flooding,” Sekhon told CTV News.

He says localized flooding is possible in areas with poor drainage like flat agricultural land.

The rain is expected to arrive in three pulses.

It’s expected to start Tuesday afternoon and continue until Wednesday afternoon.

However, Environment Canada says the snow is deep enough on the mountains to absorb moisture.

“The high elevation snowpack is well established at this point, it should be able to absorb a lot of the rainfall up there,” said Sekhon.

He says conditions are much better than they were back in November when B.C. saw widespread flooding.

“November was unprecedented. We've never seen, you know, quite that sort of situation leading to such catastrophic destruction in parts of the south coast and even parts of the southwest Interior,” said Sekhon.

However, weeks worth of built up snow and ice is expected to melt aggressively which could cause washouts near rivers, creeks and culverts.

“The rainfall itself you know this would probably show up as being a fairly run-of-the-mill moderate storm event that we’ve seen a half dozen times or more this season,” said Dave Campbell, of the River Forecast Centre.

Heavy downpours can cause flash floods and water pooling on roads, so drivers are being urged to slow down and drive for the conditions.