Sam Reynolds / McGill Tribune

Last week, as unusually hot temperatures hit Montreal, McGill students flocked to green spaces all over campus, trading winter coats for shorts and tank tops.

The peak of the hot spell hit on March 21, with the temperature reaching 25.8 C degrees, according to Environment Canada.

Wednesday’s high exceeded the record high temperature for March 19 by 10 degrees. 

“Beating a record by 10 degrees is unheard of,” Frédéric Fabry, professor of atmospheric and oceanic sciences, said. 

The unusual weather was caused by a combination of the mild winter and a north-south intrusion of a strong air current in the upper atmosphere called the jet stream,  which blocked cooler weather from reaching the east coast. 

Fabry explained that most Montreal weather travels west to east, driven by the jet stream. Occasionally the usual path of the current is disrupted by north-south air currents. When this happens, the weather gets trapped in place while the current is disrupted. This phenomenon is referred to as a block.

“We just happened to be on the right side [of the block],” Fabry said, referring to the fact that warm weather hovered over Montreal while snow continued to fall in western Canada and heavy rains pounded Texas, causing flooding. 

In a normal Montreal March, deep snow would have cooled the warm air that travelled north from the Gulf of Mexico. The mild winter, caused in part by the fact that cold Arctic air stayed farther north in Canada than usual, meant the snow was thinner on the ground and melted quickly without significantly cooling the temperature.

Fabry stressed that while there is plenty of evidence of gradual warming, this stretch of weather should not be considered proof of global warming. He pointed out that despite the mild winter in eastern Canada, Eastern Europe experienced much colder temperatures than usual.

Meteorologists can see weather coming a week or so in advance by watching air currents and monitoring the weather conditions upstream. However, predicting the types of combinations of complex phenomena that resulted in the unprecedented warm spell last week is a difficult task.

Although websites like The Weather Network were predicting warm weather, the temperatures exceeded expectations. The bout of warm weather, which brought a snow-free St. Patrick’s Day, was a pleasant surprise for most.

Frostbite, an on-campus ice cream shop, sold so much ice cream that they had to close briefly to wait until more stock arrived. The unprecedented melt also surprised the city of Montreal, which responded by starting street cleaning operations much earlier than usual this year.

In the coming week, the weather is expected to cool down again. Optimistically, Fabry pointed out that one last unexpected frost could kill off the mosquito larvae, making for a much more pleasant summer.