A giant storm barreling across Canada and the U.S. is disrupting travel in Canada’s major cities ahead of the holidays.

Air Canada is warning of snow-related cancellations from Friday through Christmas Day at the country’s biggest airport, as well as in Vancouver, Ottawa, Montreal and Quebec City. WestJet said it is canceling flights across Canada Friday, including those in and out of Vancouver and Toronto Pearson International Airport.

“We will be adapting to changes in weather conditions through the day as the storm evolves,” Montreal-based Air Canada said in an emailed statement. A number of flights were “pre-canceled” on Friday “due to the weather, reduced airport capacity and other operational constraints.”

Weather warnings from Environment and Climate Change Canada cover much of the country, part of a massive winter storm that’s causing chaos across the northern U.S. Extreme cold is expected across western Canada, with Vancouver bracing for more snow and freezing rain. High winds, snow and freezing rain are also expected across Ontario and Quebec.

Following WestJet’s announcement of cancellations, the Greater Toronto Airports Authority issued a statement urging airlines to “make every effort to address staffing provisions and crew allocations to deal with ongoing weather disruptions.” About 30 per cent of Friday’s flights in and out of Toronto Pearson have been canceled.

In Montreal, 77 arrivals and departures out of 473 flights out of Pierre Elliott International Airport were scrubbed as of 8:20 a.m. local time, spokeswoman Anne Marcotte said in an email.

Montreal is well equipped to deal with harsh winter conditions, but “unusual events, such as heavy ice or snowfall, may result in flight delays or cancellations,” Marcotte said. “Issues at other airports may also affect flight schedules in Montreal.”