FORECAST CENTRE | April long range pattern

Canadians remain in winter's icy grip (with snow) until May

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Dr. Doug Gillham and Michael Carter

Meteorologists

Friday, April 6, 2018, 12:46 PM - April has arrived, but the first few days of the month have brought temperatures much more typical of winter than spring as arctic air has dominated Canada. Milder temperatures will take hold eventually, but the warming trend will be slow to develop, as a full-on pattern change is still weeks away. In the meantime, what does the rest of April have in store? Read on for all the details, as well as a peek at the month of May.

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This map shows the temperature anomaly, or departure from normal, across North America for the first three days of April.

A blocking pattern over the Arctic has sent the coldest air on the planet relative to normal spilling across North America, centered on the Canadian Prairies. Areas in purple on this map have averaged 10 to 20oC colder than normal to start the month. The reach of the cold has been widespread, with almost all of Canada experiencing below normal temperatures to start the month.

Outbreaks of arctic air tend to be less long-lived in the spring than in winter, but a reinforcing blast of cold will help keep temperatures below seasonal for most of the country into next week. The map bellows shows our high temperature forecast for Friday (April 6th). Once again temperatures in places such as Calgary and Regina will be 15 to 20 degrees colder than normal.

During the weekend the Prairies will not be quite as frigid, but temperatures will still be 10 to 15 degrees colder than normal and below seasonal temperatures will extend all the way to Atlantic Canada.

A warm-up of sorts is on the way for much of Canada next week, but it will be brief and in most places the temperatures will not even make it back to seasonal. Milder Pacific air will spread into British Columbia on Monday and across the Prairies on Tuesday. The map below shows high temperatures for Tuesday. While central Canada is much warmer than this week, these temperatures are still on the cool side of seasonal.

However, during Wednesday and Thursday the next round of arctic air will already by surging south across the Prairies and into northern Ontario. While it will not be nearly as cold as what we have seen this week, temperatures will once again be close to 10 degrees colder than normal.

The most uncertain part of the long range forecast is for southern Ontario and southern Quebec late next week and weekend. The key will be the track of a large Colorado Low. One scenario has a stronger system tracking into the Upper Great Lakes. This scenario would bring heavy snow to parts of northern Ontario, but warm air would surge north into southern Ontario and southern Quebec and eventually reach the Maritimes.

However, if the Colorado Low is weaker and tracks further to the south, these regions will remain chilly with a northeasterly flow into the region and the warm air will remain south of the border.

Second Half of April

Regardless of how the pattern develops for late next week and weekend, it is increasingly evident that colder than seasonal temperatures will dominate much of central and eastern Canada during the third week of April and it looks like we will really struggle to have any persistent warmth during April.

While there will still be some back and forth swings in temperature, the final numbers will be on the cold side of seasonal.

Looking Ahead to May

For a more substantial pattern reversal that brings an extended period of near-to-above normal temperatures, we will have to wait until May. The exact timing of this pattern change is still uncertain, but currently we think that that most of Canada to see near normal or above normal temperatures dominate during the month of May. The most likely region to see above normal temperatures during May looks to be from the Great Lakes to the Maritimes.

Also, keep in mind that “normal” temperatures quickly rise this time of year, gaining a degree every few days. Given that fact, a transition from colder than normal April weather to near normal or above normal temperatures in May will be a rather impressive swing in temperatures.

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