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Thermal low over Great Lakes brings bursts of heavy snow to parts of southern Ontario


Staff writers
February 17, 2013 — Roads were slick as a thermal low over Lake Ontario blasted the Greater Toronto Area and Niagara region with snow Saturday afternoon and evening.


The snow made for tough driving conditions.
The snow made for tough driving conditions.

More than 10 cm of snow fell on parts of the GTA as flurries intensified into major snow bursts, with Toronto's Pearson Airport recording 13 cm.

The snow was a result of a thermal low forming over the Great Lakes -- a wintertime phenomenon that happens when cold air gathers over comparitively warmer bodies of water.

Unlike lake-effect snow-squalls, which are driven inland by straight-line winds, thermal lows are guided by slight rotation in the upper atmosphere.

"Because it's such a rare phenomenon, it can be very unpredictable," Weather Network meteorologist Elena Lappo says. 

With snow on the runway, several flights out of Pearson were cancelled Saturday, and more than 100 others were cancelled or delayed on Sunday as well.

Greater Toronto Airports Authority spokesman Scott Armstrong said the leftover cancellations from the snow should be cleared by Sunday evening, although there could be more changes to flight schedules due to poor weather in the U.S.

There were icy road conditions on many of the 400-series highways, and several accidents occurred in the GTA over the course of the storm, with some also reported on Sunday, although an OPP spokesman said he could not estimate how many were weather related.

With overnight temperatures falling below -10C, the City of Toronto issued an extreme cold weather alert to free-up extra resources for the city's homeless population. It was lifted Sunday morning.

The skies above the region were clearer Sunday, but Atlantic Canada was in the grip of another winter storm.

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