Christmas storm to bring rain, heavy snow to southern Ontario

Digital Writers
·3 min read
Christmas storm to bring rain, heavy snow to southern Ontario
Christmas storm to bring rain, heavy snow to southern Ontario

A complex winter storm is taking aim at southern Ontario, starting as heavy rain and transitioning to heavy snow over the course of Christmas Eve, with some parts of the region in for up to 20 cm of snow by Christmas Day, including some of the GTA, though eastern Ontario remains as snow. A more detailed look at the timing of this system, below.

WEATHER HIGHLIGHTS:

  • Widespread rain for southern Ontario Thursday morning into the early afternoon hours before areas across the west transition over to wet snow on the backside of the system

  • Transition to snow for the GTA expected during the later afternoon and evening hours. Heavy rainfall continues east of the GTA and for all of eastern Ontario and southern Quebec

  • Brief period of mixing or freezing rain late Thursday east and northeast of the GTA

THURSDAY: RAIN CHANGES TO SNOW AS COLD FRONT SLAMS THROUGH THE REGION

From its overnight beginnings, this system's rainfall will cover much of southern Ontario by the morning of Christmas Eve, accompanied by a surge of very mild air, as temperatures climb into the high single digits, with a few spots potentially even reaching double-digit values.

In all, much of the GTA will be in the 5-20 mm range, but eastern Ontario will be deluged with 30-50 mm throughout Friday morning.

ONRain (7)
ONRain (7)

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However, things get complicated when an Arctic cold front slams into the region through the day Thursday, bringing a changeover from rain to snow through the afternoon, as a developing surface low keeps moisture locked in place.

The Greater Toronto Area should see that switchover during the late afternoon or early evening hours, though there is still some uncertainty with the exact timing of that transition.

The heaviest snow looks to continue through the overnight, with the potential for a messy transition zone east of the GTA into cottage country that could include a swath of freezing rain.

"There will be a very tight gradient in snow totals on the eastern side of the cold air boundary, and the exact position of this gradient is still uncertain, especially for eastern parts of the GTA," Weather Network meteorologist Michael Carter says.

Eastern Ontario, including the Ottawa Valley, will stay as rain into Christmas morning.

SIGNIFICANT SNOW THREATENS SOUTHERN ONTARIO CHRISTMAS MORNING

Through Christmas Day, a widespread 10-20 cm is possible, including for most of the GTA, though there is still uncertainty about the exact location of the highest amounts.

Ontario snow
Ontario snow

Even after the system snow comes to an end, Christmas Day will be blustery and cold under the influence of Arctic air, with lingering flurries and bursts lake-effect snow expected for the usual snow belt areas.

It will still be cold for Boxing Day with bands of lake-effect snow continuing southeast of Georgian Bay and Lake Huron.

EastXmasLakeEffect
EastXmasLakeEffect

By Sunday we'll see the fair and seasonal conditions return, but also watching the potential for widespread snow early next week across southern Ontario and into southern Quebec.

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Check back as we continue the monitor the forecast leading into Christmas.