A WEATHER STAT THAT GOES ON SUMMER HOLIDAY
You hear about wind chill in winter, but it happens at this time of year, too
It’s a hot summer, and every single day the “humidex” says it feels hotter than the temperature. But does something ever make a summer day feel cooler?
What happened to the windchill calculation that makes every winter day feel colder than the actual temperature, Postmedia wondered Thursday as the temperature rose. There’s still wind in summer, isn’t there?
We asked David Phillips, senior climatologist at Environment Canada, and he surprised us by giving the cool idea a warm reception.
The trick, he says, is to find the right kind of wind — or to make it yourself through smart architecture.
Point one is to stay in the shade, he says. The official temperature is taken in shade, and sunshine may raise the air temperature above body temperature (37 C). Wind that hot just blows heat at you and makes you feel worse, like air from an oven.
“Below that, then the skin temperature would benefit from the wind blowing.” That’s because it dries perspiration, “and when moisture leaves your skin that’s a cooling factor.”
In Canadian forecasts of summer weather, “we don’t really factor in wind,” he said. “We have the humidex, and I don’t know in the States, where they have heat indexes and ‘sizzle’ indexes, whether they factor in wind.
“It’s not something that is explored” by Environment Canada. “But ... the wind does provide some relief on a hot day.
“When you go for a walk and there’s no breeze at all, you truly feel it.”
Which brings Phillips to the topic of southern countries that build breezeways.
“When I go to meetings or conferences in tropical countries, I notice that the hotel is wide open. There are no doors (to the outside). You walk right through, and the buildings will allow a funnelling effect. They take a regional breeze and will speed it up.
“Architects in hot countries understand what can provide comfort.
“And you also see in places like Savannah, Georgia, where they have big porches that overhang to get you out of the sun, but also as breezeways they are really critical.”
The University of Arizona renovated a dilapidated house on campus in 2011 and discovered that it applied this principle. Built in 1906, the house had a central living room that stretched the full length of the house and opened to the outdoor air at both ends. This created a breezeway cooling the home. The university said it’s a design feature called a zaguan that people in Mexico and the U.S. Southwest have used for centuries.
The wind explains why the air can paradoxically seem less comfortable at night, even though the temperature falls, Phillips said.
In the daytime there’s wind because the sun warms air and makes it rise, a process called convection. At night the air doesn’t rise.
“People say to me, why is it so oppressive at night when the temperature has fallen to 22 from 32? (It’s because) the ventilation is less.” Windows can be wide open and no cool air comes indoors. As well, the relative humidity is higher, “so it’s more saturated, more clammy.”
This summer is warmer than the past three summers, Phillips said. We aren’t setting heat records, but it has been consistently hot, without much rain. And when a cold front moves in, it’s only a drop of a few degrees instead of being dramatically cooler and stormy.
“It (the high) is only dropping down to 28 or 27. It isn’t dropping to 20 or 21. It shows that the cold air which might trigger thunderstorms is lacking.”
Since June began, Ottawa has had 27 days when the temperature reached 29 C. Last year for the same period there were 10 days of 29 C or higher.
We’re due for a cold front Friday evening, but the high on Saturday is still forecast to be 27 C.