Wednesday, 20 November 2013

Chinooks: The Good, the Bad, and the Windy

There are a lot of different ways in which weather can ruin your day. You can suffer through ridiculous heat waves, frigid cold, hurricanes, tornadoes, and hale the size of soft balls. The worst part about it all is that predicting the specific behavior of weather patterns is difficult verging on impossible. The last thing you want is to be surprised when you walk out your front door… That is of course unless you live on the Eastern edge of the Rocky Mountains in North America.

The weather on the leeward side of the continental divide is variable to say the least. In Canada, residents of Alberta can vouch for the fact that summers are short and mild while winter can go on for decades and flash freeze the hair on your head. Indeed, the people of the prairie come from a hardy stock. Occasionally, though some of them get to cheat their way out of winter for a few days at a time.




Chinooks (also known as foehn winds) are a Calgarian’s best friend. Over the course of a few hours, these warm winds can rush in from the mountains and lift the temperature from sub-zero to nearly tropical.  Examples of potent Chinooks seem to break all the rules of Canadian winter. During the winter of 1962 the town of Pincher Creek, Alberta was greeted by a Chinook that caused the mercury to rise by an astounding 41°C (74°F) in one hour resulting in a day-time low of -19°C and a high of 22 (-2 to 72°F). In February 1992, Claresholm, Alberta experienced a high of 24°C (75°F), one of the highest February temperatures ever recorded in Canada. These Chinooks are certainly impressive, but bragging rights in the warm winter wind department go to the town of Loma, Montana where on January 15, 1972 the temperature fluctuated by 58°C (103°F) from a low of -48 to a high of 9°C (-54 to 49°F).




For those of us who live beyond the reach of Chinooks, this is all clearly unfair. Obviously the people in Alberta and Montana and the handful of other places along the continent’s spine that experience nature’s equivalent of a “Get Out of Jail, Free” card have made some deal with Satan. Alas no, the science behind Chinooks is relatively straightforward. 





As warm, moist air from the Pacific rushes up the western edge of the Rockies, temperatures fall and water is dropped off in the form of snow. The remaining dry, cold air crests the mountains and (in the manner of cooled gases) begins to rapidly fall down the leeward side. As the air falls it gets crunched together (becomes denser) and the temperature rises dramatically. It is the same thing that happens in a piston when air compressed so rapidly that it heats up to the point of exploding, only far more agreeable for people who get in the way.




Rapidly condensing air does have its side effects, it must be said. Though it might not feel like it on the level of everyday experience, wind is very heavy stuff.  If you weighed a column of air 1 meter (3.28 feet) in diameter that extended to the top of the atmosphere you could come up with a figure of about 10 tons (22,000 lbs). Consequently, as cold air plummets down the side of a mountain, it tends to pick up speed. Chinooks can reach hurricane speeds. On November 19, 1962 a Chinook blasted through Lethbridge, Alberta at a speed of 171 km/hr (106 mph).





Summer weather in January is a perk that is not taken lightly in the great white north, but having your house blow away will put you at a powerful disadvantage when the arctic air mass reasserts itself, as it inevitably does. There may be a lot of give and take when it comes to Chinooks, but a little heat in the dead of winter is a pretty cool thing.



1 comment:

John Forrester said...

You've picture the details of good,bad and windy weather very nicely.Your details can clearly make one understand about the Celsius, Fahrenheit and the resulting factors as well with many more things. Rain gauges, data loggers, wind meters are kind of cabled weather stations for official use.