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High-impact winter weather is 12 hours away: Details here

Digital writers

Wednesday, November 8, 2017, 9:38 AM - Wednesday morning was a little frostier for many across southern Ontario, a harbinger for the real cooldown that is to come -- along with snow showers and snow squalls that are expected to be brief, but hefty.

"While the upcoming lake effect event will not bring crippling snowfall totals due to the relatively short duration (due to high pressure and drier air quickly moving in behind the cold front), we expect the snow squalls will be locally intense for several hours with strong winds Thursday evening and into the overnight in the traditional snow belts – and the bands will reach into parts of the GTA," Weather Network meteorologist Dr. Doug Gillham says.

Weather Highlights

• System starts as rain in the southwest Thursday, switching to a mix, then snow showers by late evening
• Lake effect snow squalls set up Thursday evening into Friday morning off of Georgian Bay and Lake Huron
• Worst-hit areas will see brief, but intense bursts, potentially reaching into the northern GTA
• Very cold temperatures Thursday night into Friday and Saturday morning, raising risk of flash freeze
• Weak clipper will bring the threat for rain and snow showers Saturday night and Sunday

Snow will begin as early as Wednesday evening for regions east of Lake Superior to the Quebec border, lasting through Thursday, which is when it will begin in earnest for the south.

The system starts as rain in the southeast, reaching the GTA by Thursday afternoon, then transitioning first to a rain-snow mix, then to flurries, but the late evening. Later Thursday, the system's cold winds over open lake water will make for at-times intense lake-effect snow, developing overnight Thursday into Friday as temperatures fall lower than -5oC.

"Lake effect snow squalls will diminish late Thursday night and Friday as high pressure with dry air builds in – but flurries will linger well into Friday southeast of Lake Huron and Georgian Bay, Gillham says.

The flurries are, at the moment, expected to be intense, but relatively short-lived. Still, it will make for a difficult drive for the the worst-hit areas.

"Under the most persistent bands, I expect that we will see 15-30 cm of snow and the bands of lake effect snow will extend into parts of the GTA – potentially including Newmarket, Aurora, Markham and Ajax. Travel will be hazardous along part of the 400 and 404," Gillham says.

Temperatures, it should be stressed, will plunge overnight, such that daytime highs on Friday are likely to not reach zero, and cold records are in danger of being broken both on Thursday and Friday night.

With temperatures dropping so precipitously, forecasters are warning of flash freeze potential on roads and overpasses.

"Temperatures recover a few degrees for Remembrance Day with some sun, but still well below seasonal despite some sunshine," Gillham says. "A weak clipper will bring the threat for rain and snow showers Saturday night and Sunday."

What causes lake-effect snow? Watch below:

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