Ottawa and parts of eastern Ontario are under a freezing rain warning as slick roads and sidewalks are cancelling buses and creating dangerous driving conditions.

The freezing rain, which held off overnight, is expected to begin during the afternoon rush hour on top of the more than 13 cm of snow that landed at the Ottawa airport Monday into Tuesday, according to CBC Ottawa climatologist Ian Black.

The precipitation is expected to last late into the evening, Black added, before turning to rain.

Environment Canada said a "low pressure system from Colorado will bring in another surge of moisture" leading to between three and six hours of freezing rain.

"Most areas will likely receive one to three millimetres of freezing rain, with higher amounts near five millimetres possible over the Ottawa Valley," according to Environment Canada's forecast.

Snow clearing in anticipation of freezing rain

City of Ottawa crews were busy overnight clearing snow off the roads and sidewalks in anticipation of the freezing rain. The overnight parking restriction was lifted Tuesday morning.

School buses were cancelled for the Upper Canada District School Board, the Catholic District School Board of Eastern Ontario and all English school buses in Renfrew County. Buses were also cancelled for all French-speaking public schools in Ottawa.

Exams were pushed back one day at those school boards.

Ottawa's English-speaking public and Catholic school boards do have buses running and exams are running on schedule, as do those school boards in Gatineau and western Quebec.

The weather forced the Limestone District School Board in Kingston, Ont., to dismiss students early. School buses were scheduled to pick up the students between 11 a.m. and noon Tuesday.

All afternoon exams were to be moved to Thursday, except for Sharbot Lake High School where exams will go Wednesday.

Ottawa police said they logged more than 100 crashes Monday due to the snowfall. There were no serious injuries, however.