Markham is in line for what could be the heaviest snowfall of the winter so far. Environment Canada issued a yellow snowfall warning on Wednesday, Jan. 14, for Toronto and surrounding regions, including York Region, with snow expected to start Wednesday night and continue into Thursday afternoon.

The weather agency said 10 to 20 centimetres could fall, with reduced visibility and blowing snow. It also warned of a sharp drop in temperature that would bring cold wind chills by Thursday morning.

Cold behind the snow

Environment Canada said the temperature could fall to -9 C on Thursday morning, feeling closer to -22 with the wind chill. The cold was expected to last through the day, with the wind chill still near -16 in the afternoon.

Thursday's morning commute is likely to be impacted by snow.

— Lyndsay Morrison, CTV News Toronto weather anchor

If the forecast holds, it would be the snowiest day of the season in the Toronto area. CP24 reported that the largest one-day total at Toronto Pearson International Airport so far this winter was 12 centimetres, on Dec. 26.

School boards across the GTA were expected to decide on bus cancellations and closures by 6 a.m. Thursday.

A week of swings

The warning followed several days of unusual weather. On Friday, Jan. 9, a special weather statement warned of wind gusts of up to 90 km/h in Toronto, and Pearson recorded a high of 14.1 C. That beat the previous Jan. 9 record of 11.6 C, set in 2008.

The same day, the Toronto and Region Conservation Authority, whose watersheds include the Rouge River system through Markham, issued a watershed conditions statement. It said flooding was not expected, but that rain on frozen ground and melting snow could make rivers rise and run faster than usual for two to three days. It urged people to stay away from rivers, streams and slippery banks.

On Saturday, Jan. 10, Environment Canada placed Markham, Vaughan and Richmond Hill under a special weather statement for freezing rain, with up to two millimetres of ice possible. The agency warned that roads and walkways could become icy and slippery. Pickering, Ajax, Whitby and Oshawa were under a yellow freezing rain warning.

By Tuesday, CP24 meteorologist Bill Coulter was telling viewers to "prepare your parkas" for a much colder pattern starting Wednesday night.