Monster U.S. storm system heading for Ontario, Prairies

A nasty storm system making its way north from the United States is expected to give the Prairies their first taste of winter, although a tornado watch in southwestern Ontario should end Tuesday afternoon.

This, while Toronto was expecting temperatures near 22°C and Ottawa, up to a balmy 19°C.

Parts of southwestern Ontario near Windsor are under tornado watch, while the Sarnia area remains on severe thunderstorm watch as the same cold front that led to tornado reports in Chicago on Tuesday morning enters the region. In Chicago, air traffic at O'Hare International Airport was affected by the strong winds.

Peter Kimbell, a warning preparedness meteorologist at Environment Canada, said the tornado watch would likely end late Tuesday afternoon. The watch also had residents on alert in parts of Michigan and Ohio, Kimbell said.

The same weather pattern, which originated over Minnesota, is expected to give southwestern Manitoba and southeastern Saskatchewan a significant dose of snow. Snowfall warnings remained in effect late Tuesday afternoon in many areas of those provinces.

Upwards of 10 centimetres of snow was forecast for Regina, while some areas of the province in higher elevations might see snowfall totals of about 25 centimetres. Occasional blowing snow is also in the forecast for that region.

The weather system, however, is resulting in mild temperatures in southern and eastern Ontario.

The mercury was expected to hit 22°C in Toronto on Tuesday and top out at 16°C Wednesday.

In Ottawa, there was an expected high temperature of 19°C Tuesday, with a second consecutive day of mild weather forecast for Wednesday.

Some Prairie regions, such as Winnipeg, were also anticipating higher-than-normal temperatures on Tuesday. Residents there were expecting temperatures of about 14°C for Tuesday, before temperatures dipped back toward the freezing mark for the rest of the week.

Kimbell said the type of system is not that rare, but the strength of the current pattern is what sets it apart.

"Autumn snow periods are not uncommon (for the Prairies), but the depth of this system is unusual," he said. "It's unusually strong for this time of year.

"We don't see many storms (like this) throughout the whole winter, so to have one in late October is unusual. We'd see one or two of these in November, December or January, but it's early and it's very deep.

"It will last a few days, but when I say deep, it means the central pressure is very low, which means there's a very strong pressure gradient, which (leads) to a lot of wind."

"For all of southern Ontario, wind is going to be a factor later (Tuesday) as that cold front comes through," he said. "The winds will shift and increase quite a bit, with gusts of up to 70 km/h, maybe even 80.

"If this storm were to occur in November, it would be a much different scenario with (more) snow impacts. We're doing well (in Ontario) just to have these warm temperatures and wind. It could be a lot worse if the time was a month or two later."