Weather extremes show that winter hasn’t given up just yet

With record-breaking cold in the prairies and a winter storm watch in effect for most of southern Ontario, you wouldn't know that it's spring yet, regardless of what the calendar says.

Residents of Alberta, Saskatchewan and Manitoba have had to layer on the extra winter clothes this week as a frigid arctic air-mass pushed south earlier this week, causing overnight temperatures to plummet. Several temperature records were broken on Monday morning in central Alberta and Saskatchewan, some going back to the 1940s, and more record-breaking temperatures have been seen in Saskatchewan on Tuesday and Wednesday morning as well.

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The most extreme cases were Edmonton International Airport on Monday morning, which reached a temperature of -20.0°C, breaking the previous record of -16.4 degrees from 2002, and Regina on Tuesday morning, which shattered the April 9, 1948 record of -15.6 by dropping to -20.5°C. That's not even including the wind chill, which likely made these temperatures feel closer to -30.

Further to the east, residents of southern Ontario have been dealing with a soggy week so far, with a thunder and lightning show added in on Monday night, just for effect. This wet weather is due to a series of low-pressure systems moving through the northeast, but as the cold air over the middle of the continent starts to push eastward, things are expected to get very messy throughout southwestern, south-central, and eastern Ontario on Thursday and Friday.

Heavy rainfall warnings are in effect for regions from Windsor to Haldimand (south of Hamilton), including Sarnia and London. According to Environment Canada: "Some locations within the rainfall warning have already seen in excess of 30 or 40 mm of rain as of this morning. Total rainfall amounts of 50 to 80 mm are expected before Friday."

The rest of the southern part of the province, from the shores of Lake Huron, through Toronto and the GTA, and reaching all the way east to Ottawa, Cornwall and the western St. Lawrence River Valley, is under a Winter Storm Watch.

"Poor travel conditions are expected over the duration of this event," the forecasters wrote. "In particular, the Thursday morning commute may be challenging with icy conditions on untreated roads for areas from the Greater Toronto area westwards to Lake Huron. And it may be even more problematic for the evening rush hour. Of greater concern is the risk of widepsread power outages due to downed tree limbs and power lines due to significant ice accumulation combined with northeast winds gusting to 60 km/h. There is a risk that this could be a major ice storm for an appreciable swath of Southern Ontario. Mixed precipitation is expected to persist into Friday (especially for Eastern Ontario) followed by a gradual improvement."

So, what happened to the start of spring? Last year, we were setting record-breaking warm temperatures at this time, and now this year we're seeing the opposite.

Partly to blame is a large-scale weather pattern called the Arctic Oscillation. Similar to how the South Pacific experiences shifts between El Niño and La Niña, with widely differing weather patterns for North America as a result, the Arctic Oscillation waxes and wanes over the Arctic and North Atlantic, causing the 'jet stream' to alternate between a fairly sedate flow over the north and making sudden extreme dips to the south.

At some times — in its 'positive phase' — this weather pattern causes the jet stream to stick closer to the Arctic, and southern parts of Canada experience consistent warmer weather. At other times — in its 'negative phase', like it's doing now — the oscillation causes the jet stream to dip far to the south, dragging cold arctic air far down over western and central Canada and the United States in the process. Further east of this frigid air-mass, the pattern pulls warmer air far to the north, causing much more mild temperatures (until the whole weather pattern eventually moves on to the east, of course).

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Residents of the prairies will be catching a break going into the weekend, as temperatures warm up a bit. As for east of there, it's going to be a bumpy end to the work week for Ontario, and residents of southern Quebec should unpack their winter clothes and shovels again, as they're in for a snowy weekend.

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