An updated look at the January pattern change

Monday, January 4, 2016, 8:54 PM - Many residents of Canada experienced plunging temperatures to begin the first week of the New Year, with frigid air in place for Ontario and Quebec and more on the way for the Atlantic provinces as well.

The Greater Toronto Area went back to work under extreme cold alerts and wind chills around -25°C. And although some relief from the cold is on the way later this week, the return of milder temperatures will be short lived. A looming pattern change will allow a true arctic outbreak to overrun the country, bringing a more extended period of bitterly cold temperatures next week.

Though this week’s cold snap has brought the coldest air of the season so far, it is only a brief preview of the conditions we expect as we move towards the middle of the month. In the meantime there is some good news: a return to seasonal, and even warmer-than-seasonal temperatures is expected later this week for the east. But by late this week cold air will be begin to reload in the west, as Arctic air begins to take hold.

This will set up a striking contrast across the country for the upcoming weekend. Mild temperatures will linger in the east, but as this image shows, the frigid air mass will be on the march in the west. Areas of purple over B.C., Alberta, and southern Saskatchewan highlight areas where temperatures will be more than 10 degrees colder than seasonal on Saturday. Meanwhile parts of Ontario, Quebec, and the Atlantic provinces will be 10 degrees or more above seasonal, shown in areas of brown and white.

The mild areas won’t stay that way for long however, as the Arctic front makes rapid progress across the country. The exact timing will be refined as we get closer, but as we move into early next week the coldest air aloft will push into the Great Lakes region, eventually spreading as far as the Atlantic provinces by mid-week.

As Arctic air moves in, we expect the ingredients to come together for a significant and extended period of lake effect snow. Water temperatures are still quite warm, from +5 to +7°C, which will provide very strong instability to create snow squalls in favored areas. We’ll also be watching closely for the potential for any storm systems that might develop next week. With cold air in place, any storm that does form has the potential to be a big snow-maker, with the exact impacts depending on its track.

With help from a couple of reinforcing shots of arctic air, cold conditions are expected to persist through at least the end of next week. Beyond that we’ll be watching the pattern closely, to see if frigid temperatures are here to stay, or if we can expect relief from a late-January thaw.