Calgary Mayor Naheed Nenshi says it could take days or weeks to deal with damage caused by the second summer snowstorm to hit Alberta this month.

As most Canadians ease into autumn, residents of southern Alberta are contending with massive power outages, downed tree branches and slippery roads after yet another early blast of winter snow.

The amount of damage has not yet been assessed, Nenshi said, but warned cleanup wasn't going to happen overnight.

"We don't have a sense of it yet, but certainly, depending on the part of the city you're in ... I was shocked at the damage," he said, speaking at the city's emergency operations center.

While most schools remained open, some organizations – including the Calgary Zoo – were closed for business.

The snow is weighing down trees, causing branches to snap and take down power lines. Nenshi said the city would likely lose hundreds of mature trees from the wet, heavy snow.

"We are going to see some real damage and that is an extraordinary shame," he said. "I know how hard generations of people in this community have worked to build the tree canopy, but right now our focus is to make sure those fallen ones don't hurt people and don't cause further damage."

About 10 centimetres of snow was expected to fall in Calgary throughout the day Wednesday, in addition to what had accumulated overnight. A heavy snowfall warning was in place for much of the morning, but ended by mid-afternoon.

Calgarians were already busy cleaning up after a first late-summer snowstorm brought several centimetres of snow to the city Monday --  a drastic change in weather conditions from Sunday, when a high of 25 C was recorded.

Wednesday's morning commute was messy, as Calgary police dealt with more than 50 reported crashes.

Power utility ENMAX said it deployed extra crews to deal with power outages, which at one point were affecting about 30,000 people in at least 34 neighbourhoods. The power outages also caused traffic lights to go out.

“Please drive carefully, lots of traffic lights are out,” ENMAX tweeted. “Thanks for your patience on this cold and dark morning!”

As plows and sanders continue to clean up the streets, emergency officials are urging drivers to take extra time due to slippery road conditions. The mayor is also asking commuters to stagger their commute home to ease congestion on the roads.

Calgary Fire has responded to more than 200 calls, while municipal helpline 311 says it’s received nearly 1,400 calls about problems across the city.

Both the public and Catholic school boards say schools will remain open, however, there have been reports that some schools are experiencing power issues.

The Calgary Zoo said it would not be open to the public on Wednesday, after heavy snowfall accumulated on trees and near zoo pathways.

“The safety of our guests, staff and animals is our top priority,” zoo officials said in a statement.