Above: Image © Savushkin, iStockphoto.com

This time of year, we're all dreaming of warmer weather, but some lucky students will live their dream a bit quicker — with a March Break down south. The rest of us will have to shiver through our time off with only thoughts of May to keep us warm.

There is a place in our cold country though, where students don't have to choose between long waits or expensive flights to warm up. A place where between the morning trek to school and the morning walk home, the temperature can jump from -20°C to +20°C.

I know what you're asking — where is this glorious place, how does this magical event happen, and how can we get it to happen in Winnipeg?

The quick answers are these — Alberta, Chinook Winds, and unfortunately for 'peggers, we can't.

Now for the scientific answer.

Chinook winds are a type of wind that comes to Alberta, over the Rocky Mountains, about 30 days a year. A Chinook is a warm, dry wind that can melt and evaporate snow at such a rate that it is a popular myth that the term Chinook means "snow eater" (it doesn't, it's actually the name of the native people who lived in the area).

Did you know? Chinook winds can cause an entire foot of snow to disappear in a day.

Although they can't happen in Winnipeg, Chinook winds do happen in other areas. They are called foehn winds in Europe, and are typical of rain shadows. A rain shadow is caused when wet winds blow off the ocean into a mountain range. To move over the range, the winds must rise, dropping rain and losing temperature on the windward side of the range.

Did you know? In Canada, British Columbia hosts the windward side of the Rocky Mountains, which explains the high amount of rainfall in Vancouver and the temperate rainforest.

Once over the mountain, wind is dry and, due to adiabatic warming, it warms quickly coming down the leeward side of the mountains, bringing unseasonably warm weather with it. In Canada, Alberta is on the leeward side of the Rocky's, which explains the reduced precipitation in this particular rain shadow.

Did you know? On January 15, 1972, Montana experienced the greatest jump in recorded temperatures: from -48°C to 9°C.

What's what now? Adiabatic who? Ok, you caught me trying to sneak that one by. Adiabatic warming refers to the warming or cooling rates of expanding or compressing air. As air from the ocean rises over the mountains and meets the lower pressure from the altitude, it expands and gets colder. As it moves down the leeward slope and meets the higher pressure, it compresses and warms up.

The term adiabatic means that this change in temperature has nothing to do with the nearby surroundings. Add to this the act that the dry adiabatic rate is faster than the moist adiabatic rate, and bam! Wind coming down from the Rocky's manages to warm up, despite the deep-cold environment.

So while this new knowledge may not warm you up, don't feel too badly about not living in Alberta — just imagine the amount of layers those poor students have to be prepared with! With the potential 40 degrees of temperature jump, they have to be ready with toques and tanks!

Learn More!

Check out this interactive demonstration of Chinook winds

References:

Christopherson, R. W. (2001). Elemental Geosystems. New Jersey: Prentice Hall.

Ritter, Michael E. The Physical Environment: an Introduction to Physical Geography. 2006.

First published February 19, 2009

Rebecca Spring

I am a science communication graduate. I work at an environmental organization in Toronto. In my free time, I am learning Spanish so I can travel and work in South America.


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