Alberta clipper

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An Alberta clipper, also known as a Canadian Clipper, is a fast moving low pressure area which generally affects the central provinces of Canada, as well as parts of the Upper Midwest and Great Lakes regions of the United States. Most clippers occur in winter, but can occur outside of the season; generally, off-season clippers would occur in November.

[edit] Formation

Alberta clippers take their name from the Canadian province they appear to descend from, Alberta, Canada. However, the storms usually do not actually form in Alberta. Instead, they initially impact Canada via the Pacific Ocean. They lose a good deal of their moisture through the process of orographic lift as they come into contact with the mountains in the provinces of British Columbia and then Alberta. The storms arrive over the Canadian plains with little moisture, and become entangled a cold air mass occupying the region. They then slide southward as they get caught up in the flow around the high pressure system which always inhabits cold polar areas, sending them barreling into the United States.

[edit] Effects

The storms sweep in at high speed over whatever land they encounter, usually bringing with them sharp cold fronts and drastically lower temperatures. It is not uncommon for an Alberta clipper to cause temperatures to drop by 30°F (16°C) in as little as 10 to 12 hours. Often, the storms bring biting winds with them, only increasing the effect of the newly lower temperatures. Winds in advance and during an Alberta clipper are frequently as high as 35 to 45 mph (56 to 72 km/h). These conditions would cause wind chill values to drop into the -20 to -50 Fahrenheit (-30 to -45 Celsius) range.

Snowfall amounts with these systems tend to be small (on the order of 1 to 3 inches or 2.5 to 7.5 cm), as the severe lack of moisture and quick movement inhibit substantial snowfall totals. However, several factors could combine to produce somewhat impressive snowfall totals (6 inches/15 cm or more). These factors include access to more moisture (which raises precipitation amounts), slower system movement (which increases snowfall duration), and colder temperatures (which increases the snow to water ratio). The southern and eastern shores of the Great Lakes often receive enhanced snowfall from Alberta Clippers during the winter, due to lake enhancement. The lake effect snow can add substantially to the overall snowfall total.

During the winter, Alberta clippers can occur somewhat frequently, with system intervals on the order of two to four days common during active periods.

[edit] Variations

Two variations of Alberta Clippers are Manitoba Maulers or Saskatchewan Screamers. These two types of systems are far less common than Clippers, and even when they take place they are still often referred to as Clippers. The main difference between the three is from which Canadian province they begin their southward treck.