Snow fell in Ottawa on Monday night, masking the ice below from the day's flash freeze and causing slippery conditions.

The low overnight temperature, which had been expected to reach -23 C with a windchill of -33, hit -18 C with a windchill of -30.

Environment Canada issued a snowfall warning at 8:18 p.m., saying 10 to 15 cm could fall Monday evening. That followed a weird weather day in which hours of freezing rain and rain was followed by a sudden temperature drop that led to a flash freeze warning.

Rideau Canal 5th freezing rain puddle lake closed Monday Jan. 6 2014

The Rideau Canal Skateway was closed Monday after hours of freezing rain and rain flooded the ice. (Ryan Gibson/CBC)

Dozens of people in Ottawa were treated in hospital for injuries after falling on the ice Monday, as hours of freezing rain followed by dropping temperatures made for slippery conditions on sidewalks and roads.

Ottawa Hospital's Civic campus treated 40 people injured after falls on the ice, while paramedics said they have responded to nine calls and treated four people, including two who were sent to hospital with head injuries.

Laurier Avenue was also closed between Metcalfe and Elgin streets after a water main broke, sending water gushing into the street.

The freezing rain began at about 10 p.m. Sunday and had changed to rain by 4 a.m. The rain had stopped by 9 a.m. as the temperature hit 2 C, down from 6 C earlier in the morning.​

The flash freeze began late Monday morning as the temperature dropped about four degrees in just 40 minutes, from 2 C at 10 a.m. to -2 C by 10:41 a.m., Environment Canada reported. It dropped to -8 C by Monday afternoon, when a flash freeze warning finally ended.

City of Ottawa crews clearing slush puddles freezing rain Monday Jan. 6 2014

City crews were busy clearing slush, puddles, snow and ice off roads Monday morning before temperatures dropped. (Sherry Aske/CBC)

At the Ottawa airport, dozens of departures and arrivals were cancelled and dozens more were delayed.

The Rideau Canal Skateway was closed due to poor, wet conditions, as was the Rink of Dreams at city hall and most of the region's ski hills.

Ottawa police logged 12 collisions from 10 p.m. Sunday to 5 a.m. Monday. From 5 a.m. to 5 p.m., 27 collisions were reported.

The poor conditions forced the National Capital Commission to reschedule a partial closure of the Portage Bridge for electrical work. It was supposed to happen Monday but has been put off to Wednesday.

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