"It's going to be a really difficult 48 hours in Metro Vancouver," cautions Environment Canada meteorologist Brian Proctor.
That's due to precipitation headed to Vancouver in the form of snow, rain, and freezing rain.
"It's this transition from the snow to the rain that's going to be really problematic," Proctor says.
Traffic peril brought by freezing rain
Freezing rain occurs when snow falls through a warm layer of air and melts, but then lands in freezing temperatures at ground level and turns to solid ice.
"It reaches the ground as a supercooled liquid droplet," Proctor says.
In this case, the Lower Mainland is expecting a warm Pacific storm to make landfall over the next 24 hours, while the area is still covered in an Arctic air mass that's travelled down from Yukon. Interior cities are seeing temperatures as low as the mid -40s right now.
After several days of subzero temperatures, the ground itself is frozen, and covered in snow, meaning any liquid that lands on it will freeze.
At first, more snow will fall, then freezing rain, then rain. Ice pellets may also be mixed in.
That transition will be fast, happening over a period of about two days starting tonight, Dec. 22, Proctor says.
"There'll be mixed rain and snow conditions by the end of the day in Vancouver," he says.
That means potential havoc on the streets.
'Utter peril' for transportation system due to freezing rain
"Any time you see freezing rain it throws the transportation system into complete and utter peril," says Proctor. "It's really problematic."
He advises people to stay home. If they can't he suggests people travel with a safety kit to help them in any scenario they may find themselves in.
Another meteorologist, Matt MacDonald, who works with the province, shared concerns in a post on social media that the Fraser Valley will be particularly hard hit by this weather event with the potential for 30 hours of freezing rain, calling the expected road conditions "horrific."
"The rain falling into the icebox that is the Fraser Valley will freeze on immediate contact with the ground/roads/bridge decks/power lines/structures and create an instantaneous coating of sheer ice," he wrote.
Proctor says the freezing rain will be worse for the Fraser Valley.
"The further you go (east) into the Fraser Valley the more difficult that transition is," he says, noting the next 36 to 72 hours will be particularly bad for areas in the Fraser Valley.
Structural concerns
Proctor notes a secondary concern will be roofs as things warm up. The snow will be capped with freezing rain and then regular rain will pool, adding significant weight.
On top of that, gutters may be plugged with debris, ice or snow, meaning water will be stuck on roofs leading to "structural failures."
"Make sure gutters are as clear as you can get them," Proctor says.
He also cautions people who are going out to clear the snow as the rain arrives.
"That snow can be very, very heavy," he warns, noting heart attack events tend to rise during these situations.
"Dress appropriately and take breaks."
