An ‘Omega block’ is behind Europe’s heat wave — can it happen in Canada?

The heat wave has pushed temperatures as much as 18 degrees Celsius above their seasonal average, according to the Reuters Climate Monitor.

A deadly heat wave slowly boiling western Europe this month is being driven by a weather pattern known as an Omega block, which scientists say could become more common around the world — including in Canada.

The heat wave has pushed temperatures as much as 18 C above their seasonal average, according to the Reuters Climate Monitor. Hundreds of people have died, including at least 40 in France who have drowned while swimming to escape the heat, according to officials.

“Over the region studied, this heat wave is the most severe ever recorded,” the World Weather Attribution group of climate scientists said in an analysis Friday.

Here’s what to know about an Omega block, and whether climate change is to blame.

An Omega block gets its name from how the pressure systems appear on a weather map, which resembles the Greek letter “Ω.”

In Europe’s case, a bulge of warmer high pressure has settled over the affected countries, with low pressures on either side of it — the Atlantic coast to the west, and parts of eastern Europe at the opposite end.

The warmer air gets stuck or “blocked” within that structure, as opposed to normal conditions where the jet stream carries weather systems from west to east.

“Because you’ve got this high pressure system sitting there in the centre, you have a very stable and very warm air mass because the heat is moved northward into that area,” Gordon McBean, a professor emeritus in weather and environmental studies at Western University, said in an interview.

Omega blocks typically last between three and 10 days, but can sometimes persist for weeks.

Countries including Spain, France and Germany have been seeing hot and dry conditions. Because the high pressure also suppresses the formation of clouds, there’s been little relief from the sun.

France recorded its hottest-ever temperature of 43.8 C in the small southwestern town of Pissos on Wednesday.

That day was the hottest day for the entire country on record, according to the Meteo France weather agency, which said the average temperature measured at 30 French weather stations across day and night reached 30 C  for the first time ever.

Saarbruecken, a German city near the French border, broke the national temperature record on Friday at 41.3 C.

Regions in the low-pressure areas flanking the heat wave, meanwhile, are more likely to see cooler, rainy conditions.

Britain has been been caught in the middle of the high and low pressure systems, with intense heat in the south and east and cooler temperatures in the north and west, according to the UK Met Office.

Still, forecasters extended a red alert for heat Friday after the temperature in Suffolk, England, reached 37.3 C, marking the hottest June day the country has ever seen.

Yes — and it’s already happened this year.

Meteorologists at the Weather Network say an Omega block was responsible for a late May heat wave in parts of Alberta, Saskatchewan and Manitoba. Much of the region saw highs reaching 35 C.

Another Omega block was also behind the record-smashing 21 C high that Saskatchewan reported in January 2024, the network said.

McBean said Omega blocks can be predicted with fairly high confidence before they occur, noting it’s one of several extreme weather patterns that are becoming more frequent in recent years.

The World Weather Attribution analysis said the European heat wave would ​have been “virtually impossible” without human-caused climate change.

A similar heat wave in the same month 50 years ago would have been around 3.5 C cooler than this ​one, the scientists said.

The analysis added the past week’s high nighttime temperatures were 100 times more likely to occur than they would have been two decades ago.

That’s because of the rising baseline of global temperatures made possible by greenhouse gas emissions.

The European heat wave is also occurring around the five-year anniversary of the deadly heat dome that scorched British Columbia and the Pacific Northwest of the U.S. in 2021, which saw more than 600 deaths in the province alone.

McBean said it’s important for people and officials to be aware of the increasing frequency of such heat events and to prepare accordingly.

“These are situations that are leading unfortunately to death (and) economic cost of significant amounts, and these are going to increase in the future,” he said.

“We need to adapt our ways of dealing with them,” he added, from improved warning systems to ensuring homes and buildings are designed with cooling in mind.