Alberta clipper
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An Alberta clipper is a type of fast moving storm which occurs over the northern Great Plains and upper Midwest in the United States. They usually beset the states of Illinois, Indiana, Michigan, Minnesota, North Dakota, Ohio, South Dakota, Wisconsin, as well as western Pennsylvania and New York, and in the province of Ontario. 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 of Alberta. This is where they appear to descend from, especially if one is looking at a U.S. weather map, which frequently chops off the nation of Canada. These are storms which traveled over the Pacific Ocean on the jet stream, but lost a good deal of their moisture through the process of orographic lift as they come into contact with the mountains of the provinces of Alberta and British Columbia. The storms arrive over the Canadian plains with little moisture, and become entangled with the cold air mass almost always occupying that region at the time. 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
Whether the storm is crossing Canadian territory or that of the United States, the effect is largely the same. 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. Also, the storms almost always 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). As if this were not enough, Alberta clippers also tend to bring snow with them, although since the temperatures are lower the snowflakes are smaller and therefore accumulations are less. A typical Alberta Clipper will leave approximately 2 inches (51.2mm) of snow in its wake, but exceptionally powerful ones or those acting with help from other meteorological sources, i.e., the Gulf of Mexico, can produce up to 8 inches (200 mm) of snow. Alberta clippers crossing the Great Lakes, particularly in the early winter when the water is still warm, can create lake effect snow, adding greatly to the total inherent in the system.
In winter, Alberta clippers can occur somewhat frequently, two occurring in the same week for several weeks at a time would not be considered unusual.
