Classic fall storm could bring Ontario's first snowflakes

Ontario is in for a classic fall storm, with heavy rain, strong winds and a sharp drop in temperature that could bring the season's first lake effect snowflakes to southern Ontario.

A large low-pressure system is expected to sweep across nearly the entire province beginning Thursday evening, bringing wet and windy weather. Rain will fall in the Greater Toronto Area and Ottawa overnight, continuing into early Friday.

There may also be a rumble of thunder along the Lake Erie shoreline Friday morning, adding to the unsettling start to the day.

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Rainfall should subside by Friday, but don't put away your umbrella just yet. Scattered showers may persist as the storm moves away.

Behind the system, much colder air will rush south, bringing wind gusts of around 50 km/h and a rapid drop in temperatures, particularly Friday evening. Some inland areas may experience temperatures approaching or below freezing.

The strong winds could also cause higher-than-normal wave heights along the Great Lakes, resulting in rougher conditions along the shorelines.

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The passage of colder air over the relatively warm Great Lakes could lead to lake effect precipitation downwind of Lake Huron and Georgian Bay.

The temperature difference between the chilly air and the warmer lake waters can cause bands of showers. As temperatures fall, some of the precipitation may mix with snow overnight Friday.

However, it is still too early to predict whether the rain will turn to snow and how much of southern Ontario will see it. The forecast is uncertain, but the setup will be worth watching as the first taste of winter could arrive before the weekend.

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