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Latest mild spell bringing messy mix of rain and snow to Ontario this week

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An approaching storm will force southern Ontarians to add an umbrella to their winter gear for later this week

Across the country this week, Canadians are saying good-bye to the deep freeze that settled in during the first half of February, but along with these mild conditions, some wild weather is pushing through the eastern half of the country.

Frigid temperatures and punishing wind chills had spread across the country again over the past two weeks. The prairies endured even more extreme cold and wind chills, while central and eastern Canada put up with repeated shots of snow and even freezing rain. Even along B.C.'s coastline, where at this time of year usually sees what the rest of the country would consider spring weather, temperatures in the first week of the month dropped below freezing, and actually put the words 'wind chill' into the local forecasts. It's been enough to get even the most winter-loving Canadian thinking "enough already!"

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Now, a warm-spell is creeping its way across the country. B.C. saw it first, with a return to their typical winter weather (mild and rainy), and it spread across the prairies next, delivering them from the deep freeze over the weekend. The rest of the country will enjoy it over the next few days as well, but these weather conditions are never without their caveats in a Canadian winter. A storm passing through the US Northeast dumped around 10 centimetres of snow across southern Ontario overnight on Monday, from Windsor through the Greater Toronto Area. It was more added to what's already blanketing the region and just enough to make Tuesday morning's post-holiday commute that much less fun.

The storm that brought that dumping of snow is pressing on to the east tonight, hitting southern Quebec, New Brunswick and most of the US Northeast, as it sets its sights on Nova Scotia and the rest of the Maritimes for Wednesday. It's not alone, though.

Two more storms following along directly on its heels are setting up to merge over Ontario for Thursday and Friday. A special weather statement issued by Environment Canada is warning of powerful winds from this combined storm, with heavy rain through southwestern and central Ontario, and snow, freezing rain and rain in eastern Ontario and the Ottawa valley. A separate statement for northern Ontario is advising of the potential for heavy snow north of the lakes and a mix of snow, freezing rain and rain in northeast of the lakes. The exact track of the storm will heavily influence what areas see snow, freezing rain and rain, so more will be known about this closer to when the storm actually arrives.

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All of this lovely weather is thanks, yet again, to the polar vortex and the jet stream.

The strong, swirling vortex of cold that's over the Arctic during winter has weakened this year. As a result, the normally shallow wiggles and dips of the ribbon-like jet stream (the southern 'edge' of this vortex) have become deep, looping dips that drag frigid air far to the south, while on either side of the dip, warm air is being pulled far to the north. The strength of the polar vortex changes from winter to winter, but there's some strong evidence building that the extreme melting of the Arctic sea ice in recent years could be contributing to an overall-weaker polar vortex. The latest additions come out of the Scripps Institute of Oceanography and a presentation delivered at the American Association for the Advancement of Science (AAAS) meeting this weekend by climate scientist Jennifer Francis of Rutger's University. The Scripps study shows how the rapid 'darkening' of the Arctic is contributing to the warming of that region of the world, and Francis' work points to this warming as a direct cause of these deep, looping patterns of the jet stream.

Current Arctic sea ice extent is at the lowest level seen in years, despite the extreme cold the rest of North America has been experiencing. The only years that come close are 2005, 2006 and 2011. Where will it go from here? It's difficult to say. There's still about a month of potential growth. In 2005, there was a spurt in late February and early March, although it was still below average at its greatest extent. In 2006 and 2011, values remained well below average and account for the lowest late February/early March values on record.

(Photo courtesy: The Canadian Press)

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