Canada Day hit 65-year humadex high

Here’s something that you might not believe at first: Summer days aren’t getting any hotter in Ottawa.

“Summer highs are actually less extreme than they were 70 years ago” said Rolf Campbell, a local weather expert, who has for years been tracking and analyzing Ottawa weather statistics and runs the @ YOW_Weather account on Twitter.

“Speaking from a purely statistical point of view, there’s no obvious gain (in temperatures), and if you want to be technical about it, it looks like there might be a slight decrease.”

But here’s something that you definitely will find easier to believe: This long weekend has seen record-breaking heat in Ottawa.

On Canada Day, the humidex hit 47.2 — the highest ever recorded in the City of Ottawa since it started tracking humidex levels in 1953. On Monday, the temperature let up — but only a bit: the humidex still hit 44.7, good enough to tie it for the 10th hottest day by humidex.

What’s most unusual, said Campbell, is both the duration of the heat wave we’re in — “in the last 30 years, only four have had a heat wave this long,” he said — and how all-consuming it is, with night bringing no relief.

One of the unique features of this particular stretch of hot weather is how hot the mornings have been.

“What I found interesting about specifically today is the morning temperatures,” Campbell said. Monday morning was the hottest morning that the city of Ottawa has ever recorded. Hourly temperature records only go back to 1953, but the temperatures recorded at 8 a.m., 9 a.m., 10 a.m., and 11 a.m. were all the hottest on record.

One partial reason for this, he said, was because the air has gotten moister than usual in the past couple of years. Moist air is harder to cool down and heat up, so heat stays more stable throughout the day, and into the night, than it does on drier days.

Over the last 100 years or so, the amount of rainfall in Ottawa has been increasing, and it has had the effect of shifting our climate, slightly. “We’re getting a little bit more of a maritime climate,” Campbell said. It’s a subtle shift, he said, but “it’s a little bit less continental. We’re getting a little bit more air from a southern direction.”

That means we’re getting more air coming up from the southern United States and the Gulf of Mexico, which is warmer and more humid than the more temperate air from the west.

With similar heat forecast to continue through the week, Ottawa could be looking at a once-in-ageneration heat wave, which Environment Canada defines as three or more days over 32 degrees. We could be in the midst of a stretch of as many as seven days with temperatures that high.

“The last time that happened was in 1944,” Campbell said.

And while it’s unusual, don’t expect to be rewarded with coolerthan-normal days after riding out this current equatorial stretch. Campbell’s prediction is to get used to the heat this year.