CBC Ottawa climatologist Ian Black says about 10 to 15 centimetres of snow are expected to fall in the Ottawa-Gatineau region overnight and Friday.
Environment Canada on Thursday issued special weather statements for all of southern Ontario. It calls for mainly snow to fall north of a line from Kincardine to Barrie to Ottawa.
South of that line, precipitation is more likely to be freezing rain or ice pellets, the weather agency said.
By 3 p.m. Thursday, freezing rain warnings were issued from Huron to Belleville and Kingston.
Environment Canada is calling for a low of -6 Thursday night, and it expects periods of snow to start falling after midnight. The snow will continue Friday with about five to 10 cm expected to fall. The temperature is expected to hover around -6 C Friday.
By Friday night, the weather agency expects some ice pellets to begin to fall along with the snow, with a low temperature of -8 C.
More potent storm expected Saturday night, Sunday
"After a break Saturday another more potent storm approaches southern Ontario Saturday evening into Sunday," the weather agency posted on its website.
"This next storm system is expected to tap into moisture from the Gulf of Mexico. There is a risk that this could be a major ice storm for an appreciable swath of southern Ontario."
Environment Canada said there's "considerable uncertainty" about where the storm will have the most impact, "but it appears that areas along the Highway 401 corridor have the greatest likelihood for significant freezing rain amounts."
Holiday travel is expected to be significantly impacted. The weather agency said it would continue to monitor the situation and would issue warnings as necessary.
So far, Environment Canada is calling for a mix of sun and cloud Saturday with a 40-per-cent chance of flurries, a low of -13 C and a high of -8 C.
On Sunday, snow is expected with a low of -10 C and a high of -6 C.