Temperatures are soaring, so why no heat alert?
Toronto has been sweltering for the past couple of weeks with no reprieve in sight, but the city has yet to issue an official heat alert.
George Matsumura, a spokesperson for Toronto Public Health, said there are a number of factors besides the heat to consider when deciding whether to issue a heat alert.
Those factors include wind speed, dew point, humidity and cloud cover, as well as the number of consecutive hot days.
Just because it’s 39C outside doesn’t mean an alert will be issued. If it’s 39C, there’s no wind, and there is a “humid, moist, tropical air mass,” though, it is likely that there will be an official alert.
“It’s not a simple thing,” he said.
Matsumura said the key factor in a heat alert is mortality. When it’s difficult to breathe outside due to heat and humidity, older people and small children, as well as others with health concerns like diabetes, can be in serious danger.
While there have been no official alerts this month, there hasn’t been much of a break from the heat so far this summer. Toronto has had 4 mm of rain this month, and July generally gets about 74 mm on average, said Peter Kimbell with Environment Canada.
“It’s been almost two and a half weeks now with very little rain, so the question becomes ‘How long can we go with very little rain?’”
He said there might be a chance of some rain Sunday or Monday, but can’t say so for sure.
This hot dry weather makes a lot of people grumble about heat waves. The city’s term for heat waves is “extreme heat alert,” of which there have been none so far this year. There were 11 last year, compared with only two in 2009.
“We don’t have a very well-defined criteria for a heat wave,” Kimbell said.
“There are varying definitions. The best I can say is it’s going to be sunny and warm the next few days with a good bout of heat and uncomfortable conditions this weekend. Before then we’ll have more pleasant weather where we can sleep at night — lows will be 15, 16, 17 degrees.”
Kimbell added that there is no real explanation for why heat waves happen, other than to say:
“Weather is inherently variable.”
Last year there were 11 extreme heat alerts, compared with only two in 2009.
--Sarah Ratchford, Staff Reporter