Calgary drivers contended with a slippery, slow morning commute on Thursday as the city sits in the middle of a swath of southwestern Alberta that's in the path of a winter weather system.

The snow contributed to 17 collisions on Calgary streets from midnight to 8 a.m., three of them involving injuries.

From 9 p.m. Wednesday to 4 a.m. Thursday, there were 51 crashes, 11 of them causing injuries, Calgary police say.

An upper low from Vancouver Island is expected to continue moving east, dropping 15 to 25 centimetres of snow in Calgary and up to 40 centimetres along the Alberta foothills by the weekend.

"Snow will intensify this afternoon and tonight and continue into Friday before gradually tapering off," Environment Canada said Thursday on its weather alerts website.

Wednesday night saw just 2.2 centimetres accumulate, but the agency says there could be heavy snowfall on Thursday, with five to 10 centimetres falling, and flurries continuing on Friday and Saturday.

Environment Canada says as much as 40 cm of snow could fall along portions of Alberta's foothills by Saturday. (Environment Canada)

"Be prepared to adjust your driving with changing road conditions. Visibility may be suddenly reduced at times in heavy snow," Environment Canada said.

Snowfall warnings are in effect for:

Calgary.

Airdrie, Cochrane, Olds and Sundre.

Cardston, Fort Macleod and Magrath.

Crowsnest Pass, Pincher Creek and Waterton Lakes National Park.

Hinton and Grand Cache.

Kananaskis and Canmore.

Nordegg.

Okotoks, High River and Claresholm.

​Environment Canada said it's keeping an eye on the approaching storm and may adjust its forecasts.

"Snowfall warnings may need to be expanded east later this week as the system develops," the agency said.