Rainfall warnings for Metro Vancouver and Fraser Valley

Vancouver -

Environment Canada has issued a number of rainfall warnings for the Lower Mainland this weekend.

Seventy-five to 150 mm of rain is expected, depending on what part of the region you’re in.

Howe Sound and the North Shore will be hit the hardest, the warning says.

The downpour is expected to continue into Saturday night with a short break Friday evening.

“Two successive frontal systems will cross the south coast between today and late Saturday night, with high water content associated with an atmospheric river flowing off the Pacific Ocean,” Environment Canada's statement says. 

Armel Castellan, a warning preparedness meteorologist for Environment Canada says an atmospheric river is not like a typical storm, because it feeds moisture up from the subtropics.

“You're basically being sandwiched all of that moisture between a big high pressure off of California, and a huge low pressure in the Gulf of Alaska. And in between the two, you've got this filament of moisture coming up from the southwest towards our coast, and it's really like a fire hose,” Castellan explained.

High winds are also a possibility in some areas.

“The main event is actually overnight into Saturday where the highest intensities of the rain are going to come,”said Castellan. 

Temperatures are expected to climb over the weekend which would lift freezing levels on local mountains near 2,500 metres.

Melting snow would create runoff, which could cause flooding in some areas due to higher water levels in streams.

Heavy downpours can cause flash floods and water pooling on roads.

“If visibility is reduced while driving, turn on your lights and maintain a safe following distance,” wrote Environment Canada.

Drivers are being urged to leave extra time on their commutes over the weekend in anticipation of what could be dangerous road conditions. 

“It's definitely a reminder for everybody to be extra vigilant out there and make sure that you're taking the precautions. Even securing your own home by making sure that you've got your eaves cleared so that you're not dealing with a backlog of water in your gutter system,” said Castellan.

FALLOUT FROM HOT, DRY SUMMER

B.C.’s record-setting summer of hot and dry conditions is expected to play a role in this fall’s storm season.

“A long drought has a hydrophobic tendency for the soil, meaning it no longer can absorb moisture the same way than it does in the wet season,” explained Castellan.

The devastating wildfire season is also expected to have a major impact.

“Then you add on top of it wildfires scarring, in the burn scars, and then you can have essentially a lot of runoff very quickly. So those are things that are of concern. Potential for landslides goes up,” said Castellan.

POSSIBILITY OF INCREASED POWER OUTAGES

BC Hydro says it’s monitoring this weekend’s storm closely and will have increased staffing.

“We're anticipating a lot of rain to fall, and our crews are ready to head out and address any outages that come up at a moment's notice as quickly and as safely as possible,” said Kyle Donaldson, a spokesperson for BC Hydro.

He says last summer’s drought could also cause more outages this fall.

“The vegetation is extremely dry, if not dead in some areas. All of this rain is going to really saturate the ground and could present a problem. With just a little bit of wind, some of these damaged or dead trees could be knocked over a lot easier than in years past,” Donaldson explained.

He says crews will respond to outages as quickly as possible, but is encouraging all British Columbians to have a first aid kit, food and water, extra batteries on hand just in case.

“If you come across a downed power line over the next couple of days, the best thing to do is stay away. Stay at least 10 meters away. Call 911 immediately and you should consider it live,” he warned.

LONG-TERM FORECAST

Looking ahead to the long term forecast, Castellan believes a La Niña is likely coming this winter.

A La Niña is an oceanic and atmospheric event that involves the cooling of surface ocean waters, which may result in colder temperatures and snow.

“It will likely be weak, not too strong. Therefore the impact might not be extreme, but it sure does kind of load the dice if you will, to potential for snow events right down to sea level in places like Vancouver, Victoria and Nanaimo,” Castellan told CTV News.