As Canadians across the country officially welcome fall, residents in some parts of Alberta should brace for snowfall in the second half of this week.

Calgary could see snow on the ground on Friday through Sunday because of a surge of Arctic air, reports The Weather Network. The Rockies will likely see hefty accumulations of snow through Friday.

Environment Canada’s Dave Phillips predicts western Canada will experience cooler temperatures while the eastern part of the country is in for a relatively warm fall.

“It’s hard to define what fall is,” the agency’s senior climatologist told CTV News Channel on Monday, the first official day of the season.

“We think that in eastern Canada it will be milder than normal, it will be October mild. We might see more wet conditions because of remnants of hurricanes and more storm activity,” said Phillips. “In western Canada, I think they aren’t seeing something as pleasant as that. They’ll see a cooler than normal beginning to fall.”

Before you get your hopes up about a pleasant season in the east, Phillips warns: “fall is a tough season to get accurate. Fall is fickle.”

Last year, he said we had fall weather in September, but October and November were “more winter-like and that made winter feel long.” He thinks this fall season will be better than last.