A surprise storm dumped a record amount of snow on Calgary in time to make Thursday's morning and evening commutes a slow, slippery slog.

The total accumulation of about 23 centimetres beat the record for snowfall on April 10, which was set in 1912 at 15 centimetres.

More than 20 centimetres of snow fell in just a few hours on Thursday.
(Glenn Francey/CBC)

The storm had already dumped 15 centimetres by 10 a.m. The sun peeked through for a few hours just after noon, and then the snow returned in full force by late afternoon. All of it caught residents and forecasters off-guard.

"It really only affected Calgary and the immediate surrounding area," explained CBC News meteorologist Kalin Mitchell. "You can kind of compare it to sort of like a thunderstorm. And the weather models are notorious for missing small-scale events such as this."

Emergency medical services and the fire department were called to about 30 vehicle collisions, but no major injuries were reported.

Several city buses were involved in accidents, mostly where cars slid into them, said Calgary Transit spokesman Ron Collins.

"Certainly, in some communities that are hilly we've got some issues with buses trying to manoeuvre uphill," he said. "In a lot of the areas of town, traffic has crawled to a stop almost and so our buses are also obviously caught in traffic just like everybody else."

Calgary buses had a hard time navigating hills and slippery roads Thursday morning.
(Glenn Francey/CBC)

The city asked drivers to slow down especially around intersections, bridge decks, ramps and overpasses as traffic came to a virtual standstill on many major roads.

Additional crews were called in to help plow and salt city roads.

"Plows were out there. I had graders out there. I had the trucks putting down the salt and we just couldn't keep on top of it, it was coming down so hard and so fast," said Ryan Justin, the city's manager of road maintenance.

Two semi-trailers jackknifed near the HeatherGlen Golf Course in Strathmore.

Many flights were delayed or cancelled.

Children make their way to school in Calgary in Thursday's heavy snowfall.
(Chris Bolin/Canadian Press)

"There's going to be the residual effect for the rest of the day as airlines catch up with their schedules," said Bryce Paton, spokesman for the Calgary Airport Authority.

By late Thursday, taxi and tow-truck companies were reporting waits of up to three hours.

City officials are watching for flooding risks if there's rain, as well as for rapid freezing, which could block water basins.

The fire department is reminding people to extend the downspouts from their eavestroughs to divert melting snow from their roofs and away from their homes to reduce the chances of basement flooding.

Forecasts are calling for temperatures to climb to 20 C this weekend in Calgary.