Ottawa

How extreme cold warnings vary across Canada

Toronto and Ottawa had identical wind chill forecasts Friday morning, but one region got an extreme cold warning from Enviroment Canada and the other did not.

Toronto and Ottawa had identical forecasts, but only one got a warning

The extreme cold warning threshold varies by region: it's –30 in southwestern Ontario, –35 in eastern Ontario and –40 in Alberta and northern Ontario, for example.

On Friday, people in both Ottawa and Toronto were struggling under another cold day with temperatures that could cause frostbite. 

Ottawa was a touch colder, but both cities faced a windchill that made it feel like –32 C. 

Toronto had an extreme cold warning from Environment Canada, while Ottawa did not.

Dave Phillips, senior climatologist at Environment and Climate Change Canada, said the department keeps average temperatures in mind when it sets thresholds for warnings.

"Their average winter weather is a little bit more cold, so a threshold for issuing an extreme cold warning would be different in southern Manitoba, would be different in the Ottawa Valley, than it would be in the Toronto area," he said.

Environment Canada has different standards for when a cold weather alert is triggered. At -30 C, Toronto has the lowest threshold for an alert in Canada. (Evan Mitsui/CBC)

In southern Ontario, including Toronto, the wind chill or temperature has to be forecast to hit –30 for at least two hours before an alert is issued. In Ottawa, it has to hit –35, which is the same standard as coastal B.C. and Atlantic Canada. 

In Montreal, the temperature has to fall a little further still to –38, but that won't cut it in northern Ontario and most of the Prairies where it has to fall to –40 before the alarm is sounded. 

And in Nunavut and the Arctic islands, it has to fall all the way to –55 before the agency issues an alert.  

Phillips said the agency takes in mind that certain weather is much less expected in some parts of the country, and people are less prepared.  

"They may not own the garments — the balaclavas and the snow pants and the parkas and long underwear, for example — where they certainly would in the north and so they are probably better equipped to handle those kind of cold conditions," he said. 

In Yukon the weather has to hit -50 C for an alert to be issued. (Submitted by Luc Garceau)

The standards also apply to other warnings. The agency tells Torontonians to bundle up at a warmer temperature than anywhere else in the country, but it doesn't trigger a heat warning there nearly as quickly as it would elsewhere. Fog has to be forecast to last for 18 hours in Atlantic Canada before an alert is issued, but only six in the rest of the country. 

Phillips said the warnings are meant to tell people to take extra precautions, and you can't do that all the time. 

"You don't want to issue an extreme cold warning every day of the year. People will tune you out. They just won't take precautions."

With files from Andrew Foote