A weather pattern that favors low pressure systems moving southeastward out of Canada into the northern plains and Great Lakes regions of the United States has characterized January, 2014. These systems are called Alberta Clippers for their place of origin, the province of Alberta in west-central Canada.
Alberta Clippers: Steered By the Polar Vortex
When the polar vortex takes up a position in eastern Canada, as it has this winter, the jet stream flow over central and western Canada is from the northwest, and disturbances within the jet stream spawn fast-moving low pressure systems that dive south and east.
After passing through the midwest, Clippers can take a number of paths, including one that involves rapid development into a major storm along the Atlantic coast.
Alberta Clippers: Normally Light Snow
The Great Plains and midwest are far removed from any source of atmospheric moisture. In the summer, some humid air can reach the area from the Gulf of Mexico; but in the winter months, this source is shut off due to the prevailing flow of air from the west and north. The result is that both Sioux Falls, South Dakota and Minneapolis, Minnesota have monthly melted precipitation totals of less than an inch in January and February.
Even Chicago, which receives lake-effect snow, gets barely four inches total for the two months. The Clippers are able to squeeze some moisture out of the atmosphere, and that moisture is in the form of light, fluffy snow that the wind blows around easily. This means the northern plains and Great Lakes regions may seem like snowy places, but the total accumulation of moisture is minimal.
Alberta Clippers Can Take Different Paths
When a Clipper enters the northern plains, it is embedded in the polar vortex and has a southeastward motion. As it rounds the bottom of the trough (dip in the jet stream) formed by the polar vortex, the Clipper turns eastward through the midwest. From there, it can take one of several paths. Some Clippers turn northeast and head into eastern Canada; others continue east rapidly and disappear into the Atlantic; finally, some, fed by the energy of the warm Atlantic Ocean, intensify into deep low pressure centers and move up the eastern seaboard. We call these Clippers, northeasters (nor’easters to native New Englanders) because the prevailing winds along the coast which bring heavy snow and rain are from the northeast.
The Aftermath of a Clipper
Often, the most troublesome weather associated with an Alberta Clipper occurs after its passage. The winds turn to the northwest and this has two effects:
- The northwest wind ushers in a new surge of cold air. In the case of winter, 2014, with the polar vortex displaced so far to the south, this air is extremely cold — dangerously so.
- The northwest wind blows across the Great Lakes, creating lake-effect snow on the south and east shores. As long as the lakes are not frozen, the cold air blowing over the warm (relatively) lake waters can pick up large amounts of moisture which is then deposited as snow on the windward shores. Cities such as Cleveland and Buffalo are often in the path of snow squalls which can produce snow depths measured in feet.
Alberta Clippers: Weather, Wind, and Snow
If you live in Alberta, you will hardly notice the effects of the Clippers named for your place of residence. But if you live in the northern plains, midwest, or Atlantic coast, you should be aware of the weather they can produce.
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