Environment Canada has issued rainfall warnings for B.C.’s south coast with an atmospheric river in the forecast for the weekend.
The storm system will bring heavy downpours beginning late Friday night.
“Once that rain comes in, it’ll just quickly ramp up. And through Saturday, the rain intensity is going to be most likely at its highest, and that will continue for pretty much the entire day on Saturday,” said Colin Fong, a meteorologist for Environment Canada.
Fong says it will feel like the region is being hit with a firehose with two pulses of heavy rain.
The storm will taper off Sunday afternoon as the atmospheric river pushes southeastward and weakens.
The rainfall amounts will vary widely across the region.
Sixty to 75 millimetres are forecast over central sections of Metro Vancouver, while higher amounts up to 120 millimetres can be expected over Howe Sound and higher terrain of northern sections of Metro Vancouver.
Southern parts, including Surrey and Richmond, may see about 30 to 50 millimetres.
It will dry out on Monday, but that’s not expected to last.
“Big picture-wise, we are still looking at pretty much an active wet pattern through next week,” said Fong.
Heavy downpours can cause flash floods and water pooling on roads.
Environment Canada is reminding drivers that if visibility is reduced while driving, turn on your lights and maintain a safe following distance.
“When it comes to such a short-duration, high-intensity event – when it comes to atmospheric rivers –we’re always concerned about flooding,” explained Fong.
Avoid fast-moving water
The B.C. River Forecast Centre has issued a high streamflow advisory for the south coast, including Vancouver Island.
Advisories are put in place when river levels are rising or expected to rise rapidly, but no major flooding is expected.
“We’re expecting streamflow peaks Saturday into Sunday, depending on the timing of the rain,” said Natasha Cowie, a hydrologist at the centre.
Cowie says the atmospheric river will be atypical and there are a number of favourable factors. Temperatures are cooler so freezing levels are projected to increase, meaning there will likely be minimal snow melt. The snowpack is also more mature at this time of year.
“That established snowpack is going to be somewhat resistant to melt. It’s going to have capacity to absorb some of the water and absorb more of that melt,” explained Cowie.
“We’ve had kind of a quieter period of weather. So they’re not already high, so there’s going to be some capacity within the stream channels as well to absorb that additional runoff input,” said Cowie.
Localized flooding in smaller streams is a possibility this weekend.
“There’s going to be definitely some dramatic rises in streamflows. Even if that doesn’t get to the point of flooding, they’re going to be coming up really quickly,” warned Cowie.
She’s urging people to stay away from riverbanks which could become unstable in the rain.
“If you are walking a pet close to a river, keep a really close eye on them. Keep them leashed and just be very aware and just watch out,” Cowie told CTV News.
She says fast-flowing waters can sometimes be misleading.
“You may not see there may be really active weather going on upstream, and it’s not raining a whole lot where you are, but that can still translate into some pretty big changes and pretty rapid changes in water level and in the velocity of the stream flow,” said Cowie.
An atmospheric river last October caught many people off guard when it became more intense than what was originally forecast.
A man died after he was swept away in the Coquitlam River. His body was found days later by search and rescue crews.
Several homes on the North Shore also suffered flooding and mudslide damage.
Environment Canada says while spring is around the corner, more atmospheric rivers are possible in the near future.
“Spring is no stranger to wet weather here in Vancouver, and I imagine most people aren’t either. So I would just say don’t pack away your rain gear just yet,” said Fong.
