As Ontario braces for a major storm, Toronto's expected to get off light — here's why

As parts of Friday evening, Torontonians are expected to face far less snowfall — and wake up to even less of it in the morning, meteorologists tell the Star. Toronto's geographical location and its urban development mean the city is often spared the worst of winter storms while enjoying a more temperate climate than the rest of the province, experts say.

Here's why — and what Torontonians can expect from the Friday. Dave Phillips, a senior climatologist for Environment Canada, said a six hour long storm will hit Toronto around 6 p.m. EST Friday, delivering five to ten centimetres of snow. That being said, residents can expect to wake up Saturday to just a dusting of white, Phillips continued, as warmer overnight temperatures should turn the snowfall into rain, melting most of the accumulation.

"It's sort of a rain sandwich," he said. "We're going to start with snow, then rain. So that snow will be assaulted by all that rain and the warmer temperatures, (melting most of it)." As cooler morning temperatures lead to light snowfall early Saturday, "we might see a dusting of snow in the morning," Phillip continued, "even though we're likely to see over 10 cm (overall in Toronto)." In contrast, hard hit areas including the Ottawa valley are expecting 15 to 30 cm of snowfall, he added.

Chris Scott, chief meteorologist for The Weather Network, told the Star people in the Greater Toronto Area could see "quite dramatic" differences in snowfall depending on where in the city they live, with regions along Lake Ontario like Scarborough down through Burlington expecting no more than five centimetres of "heavy, wet snow." "However, by the time you get north of highway seven, you're likely to see over ten centimetres," he continued.

Lighter, lake effect snow is expected through Saturday going into Sunday, he said. According to Scott, Toronto often sees less snowfall and warmer temperatures than the rest of the province because of its proximity to Lake Ontario and its relatively low altitude. Because the lake is still liquid, its vast reserves of water help to regulate the temperature of the surrounding area, Scott explained.

In the winter, the wind blowing off the lake is warmer than the surroundings, helping to raise temperatures. This is why there's such a dramatic difference in expected snowfall as you approach the lake, he said. "Another factor is elevation," Scott said. "Most people (understand) that when you go up, you get colder." Because Toronto is geographically lower than other parts of the province, it is usually warmer, he said: "By the time you get up to the Niagara Escarpment, you tend to lose about a degree just because of that elevation change." According to Phillips, the urban heat island effect also plays a role.

City infrastructure, from roads to buildings to bridges, tend to absorb and re release heat at greater quantities than natural environment, causing more developed areas to become warmer on average than rural locales. That said, the heat island effect doesn't apply to Friday's storm, Scott added, as the system is expected to overpower the effect through "heavy precipitation." On the flip side, our proximity to the lake can backfire should a cold, eastern wind blow across the water.

As the cold temperatures pass through the humid air above the water, it can pick up the water vapour and turn it into snow — what's known as lake effect snow, Scott said. Rare, lake effect snow can result in Toronto seeing more snowfall than the rest of the province, as , when the city logged more snow than anywhere else in the province.

"As is normally the case, with (Friday's) storm, Toronto might be in the lower end of snowfall — but it doesn't mitigate the fact that there is real impact for everyone to come tonight," Scott said..