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 and parts of the Upper Midwest and Great Lakes regions of the United States^[1]. Most clippers occur between December and February, but can also occur occasionally in the month of November. Alberta clippers take their name from Alberta, Canada, the province from which they appear to descend, and from clipper ships of the 19th century, one of the fastest ships of that time.^[2]

Contents 1 Formation 2 Effects 3 Variations 4 See also 5 References 6 Further reading 7 External links

[edit] Formation

A clipper originates when warm, moist winds from the Pacific Ocean come into contact with the mountains in the provinces of British Columbia and then Alberta^[1][3]. The air travels down the lee side of the mountains, often forming a chinook in Alberta, then develops into a storm over the Canadian prairies when it becomes entangled with the cold air mass that normally occupies the region in winter. The storm then slides southward and gets caught up in the flow around the mass of high pressure which always inhabits cold polar areas, sending the storm barreling into central and eastern areas of North America^[4].

Ironically, the chinook which in part originates the Alberta clipper usually brings extremely warm weather (often approaching 21C/70F in the depths of winter) to southern Alberta itself, and the term is therefore not in common use in Alberta.

[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 of 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^[4].

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^[4].

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.^[5][6] 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 trek.^[7]

[edit] See also

• Snowsquall
• Ground blizzard
• Windchill

North American weather patterns

• Nor'easter
• Panhandle hook

[edit] References

[edit] Further reading

• Williams, Jack: The Weather Book, 1997, Vintage Books, ISBN 0-679-77665-6.
• Dunlop, Storm: The Weather Identification Handbook: The Ultimate Guide for Weather Watchers, 2003, The Lyons Press, ISBN 1585748579.

[edit] External links

• Extratropical Lows: Clippers Meteorology Department of the University of Illinois