Chinook

Katherine is standing at the window, looking out at the snowfall. It's been snowing all morning, periods ranging from thick and heavy to light wisps. But it's here, and the Chinook wind has gone, the cold Arctic air creeping back over southern Alberta, the chill of winter once again falling over the land.

Most people who haven't experienced it really don't understand what a Chinook, or more properly a Chinook wind, really is. Leonardo Dicaprio experienced his first when he was here filming a movie last year, fearfully attributing the dramatic weather change to global warming. He didn't realize that these weather patterns which bless Calgary with wonderfully warm days in the midst of an icy winter have been happening for tens of thousands of years.

The Chinook wind is a wind off the Pacific Ocean, heavy with moist air, which rises up the slopes of the Rocky Mountains. As the air rises, it loses its moisture as rain or snow. Pressure from more air coming behind pushes the air mass continually higher and higher, until, now a dry, warm air mass, it tumbles down the eastern slopes of the Rockies, funneling through the river valleys, blasting out over the flat prairies, raising temperatures dramatically in a period of hours, or even minutes.

Calgary and environs sit right in the path of this wind, right in the midst of the Bow River Valley, a natural funnel, concentrating the winds near the mountains and exploding them over the plains at forces sometimes nearing hurricane levels. These winds have been known to blast windows out of office towers, flip over trucks on the freeway, and melt a foot of snow in little more than a few hours.

Coastal sailors know of these winds, and their cousin the Katabatic Winds. Katabatic winds are cold air masses rushing down from glaciers, typically out to sea. Adiabatic air masses are warm, rising winds which climb inland over the mountain tops. Both produce rugged air over inland waters, sometimes dangerous enough to destroy boats and bring death to the crews, both hit the ground hard, pushing down trees and destroying buildings. Both happen in BC and Alberta.

I'm glad to see a Chinook. I love the warmth, the sun, the arched cloud patterns which rarely rain. Unfortunately the Chinook turns the streets into muddy slush, the playgrounds into puddled pools of melt. Fortunately the cold returns soon after, sometimes bringing fresh snow, turning the melt into ice and, when there is no snow, drying out the roads.

I love the weather, here, at sea, on the coast, in the mountains. It's forever changing, forever renewing, forever molding our life, and our planet.