Canada hit with record-breaking heat and cold — at the same time. Is this normal?
What differentiates the current situation is the extremes, say meteorologists
This week saw people in Western Canada posting videos of snowfall accumulation to social media, while students in New Brunswick were let out of school early because of the extreme heat as the west experienced record-breaking cold at the same time eastern Canada was sweltering under a heat dome.
On June 19, Alberta set 13 new record low temperatures. About 380 kilometres west of Edmonton, Hendrickson Creek had the biggest drop, with a new daily minimum record of -2.7 C.
That same day, over 100 heat records were broken across the eastern part of the country. Ontario, Quebec and the Atlantic provinces saw jumps in maximum temperatures. While some records were broken by a fraction of a degree, others were as much as 7 C hotter than previous records.
Is this normal?
When asked if such disparity in temperatures across the country was normal, Environment and Climate Change Canada (ECCC) meteorologist Ken Dosanjh said that the short answer is actually: yes.
These fluctuations in atmospheric circulation patterns are normal, he explained. However, he says highs and lows as extreme as the ones we've been seeing are unusual for this time of year.
"It's definitely an abnormal heat event this early in June," he said.
Kerri Lang, a warning preparedness meteorologist for ECCC, pointed out that Canada is a huge country and said it's common to have this "seesaw" pattern of ridge, trough, ridge, trough — which, in the summer, translates to alternating warm and cool temperatures — created by a wavy jet stream.
In March, for example, a low pressure system brought snow to western Canada and unseasonably warm temperatures to southern Ontario and Quebec.
What differentiates the current situation, says Lang, is the extremes. "They're breaking all-time records, so there is something more that's going on," she said.
Atmospheric circulation patterns
Lang explained that a combination of the jet stream, a big high-pressure ridge and the long days of intense sun due to the summer solstice are responsible for what's been happening this past week.
The jet stream is high up in the atmosphere and separates the colder air to the north and warmer air to the south. It typically moves like a river, flowing west to east in a relatively straight line.
But scientists have noticed that the jet stream has become less stable — and less straight. As it dips across the country it makes it hot in the east, which is below the jet stream, and colder in the west, which is above it.
"These jet streams are really important for driving our weather systems," said Dosanjh. "This [current] jet stream, however, isn't uniform and creates things like troughs and ridges."
He describes troughs as cool, wet weather, while ridges are typically made up of air that's drier and more stable.
Ridges are often associated with nicer weather, but can also bring thunderstorms as well — like the ones Toronto saw earlier this week.
Dosanjh said that this week was an extreme case of ridge because of the high pressure that has been centred over North America, causing the heat wave.
Lang says the heat is reminiscent of the 2021 heat dome in B.C. The deadly heat lasted almost a month, with temperatures soaring as high as 49.6 C and wildfires burning throughout the province. Like the current situation, there was also a high-pressure ridge and intense heat from the summer solstice.
That event was at least 150 more likely due to human-induced climate change, attribution studies have shown. Other studies have also called the recent extreme heat in western North America virtually impossible without climate change.
This current ridge is also having an impact on western Canada's trough.
"The ridge in the east is allowing the trough in the west to over the prairies to really persist, which is why they have been kind of feeling that cool effect," said Dosanjh.
He clarified that Western Canada will soon be feeling the effects of a ridge, meaning temperatures will rise but shouldn't be record-breaking.
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