How chinook winds bring warmth to southern Alberta

Calgary almost broke a 101-year-old temperature record for Valentine's Day as chinook winds continue to bring warm winds to southern Alberta this week.

• If yousnap a great chinook picture, send it to calgaryphotos@cbc.ca

The forecast was for a high of 13 C, which would have topped the previous record high of 12.2 C reached on Feb. 14, 1916, according to Environment Canada meteorologist Kirk Torneby.The temperature only got to 11.9 C in Calgary on Tuesday.

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While the temperature spikes aren't always so dramatic, chinooksare more frequent than you might think.

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Torneby says calculations done by his Environment Canada colleague, Dave Phillips, showed that Calgary sees about 25 chinook days per meteorological winter which is December, January and February.

"So that's about one every three or every four days," he said.

But it's not quite an exact science, Torneby admits, since it's difficult to quantify exactly what sets a chinook apart from any other winter warm-up.

Chinooks hard to define

"It's hard to define a chinook, per se," he said.

"Basically a chinook is when warm, and very dry wind blows down the eastern slopes of the Rockies."

The warming effect can be very dramatic, with temperature swings of 20 to 30 degrees not uncommon, Torneby said.

Warm air gliding off the mountains creates the chinook'stell-tale arch, revealing a strip of skyalong the horizon between the ground and a straight line ofcloud cover.

"There's a bit of a wave that develops in the atmosphere, a subsidence wave that creates a very sharp line on it," Torneby said.

"And why they call it an arch?I guess if you look at it from a satellite imagery, there's a very sharp definition closer to the Rockies, and it kind of spreads out as it gets further to the east."

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In North America, the weather phenomenon is most pronounced in southwestern Alberta.

But similar wind patterns give people in other parts of the world a break from winter, Torneby says.

In Switzerland, they call it foehn. And in Argentina, it's known as zonda.

"I think in North America, chinook is the name they gave it because it coincides with an Aboriginal name of snow eater," he said.

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