Alberta clipper
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An Alberta clipper, also known as an Alberta low, Alberta cyclone, Alberta lee cyclone, Canadian clipper, or simply clipper, is a fast-moving low-pressure system that originates in or near the Canadian province of Alberta just east of the Rocky Mountains and tracks east-southeastward across southern Canada and the northern United States to the North Atlantic Ocean.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name="cdnency">Template:Cite encyclopedia</ref>
Alberta clippers constitute a major winter-season storm track for extratropical cyclones in the Northern Hemisphere, tracking across the continent in 2–3 days while affecting weather in parts of the Prairies and central provinces of Canada, as well as the Upper Midwest, Great Lakes, and New England portions of the United States. They are associated with cold, dry continental air masses and generate small-scale, short-lived weather events typically producing Template:Convert of snow in a three to six hour period. However, they can precipitate sudden temperature drops and sharp winds leading to local blizzard conditions, especially when interacting with moisture from the Great Lakes.<ref name="Thomas">Template:Cite journal</ref><ref name="Thurlow">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
EtymologyEdit
Alberta clippers take their name from Alberta, the province from which they appear to descend, and from clipper ships of the 19th century, one of the fastest ships of that time.<ref name="cdnency"/><ref name=douglas>Template:Cite book</ref>
The term was coined in the late 1960s by Rheinhart Harms, a meteorologist at the U.S. National Weather Service Office in Milwaukee, Wisconsin, who noted the rapid speed of these snow-producing storms as they moved across the Dakotas from Alberta towards the Great Lakes.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> Its colloquial use spread among U.S. and Canadian weather forecasters in the early 1970s.<ref>Template:Cite news</ref> It entered the scientific literature around the 1990s.
Storms beginning their southward treks from other Canadian provinces, far less common than clippers, are often still referred to as clippers, or by the fanciful names Saskatchewan screamer, Manitoba mauler or Ontario scari-o.<ref name = "cdnency" /><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
FormationEdit
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.<ref name="Thurlow"/> 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 that region in winter. The storm then moves east-southeast riding the jet stream, and passes off the upper Atlantic Coast, normally north of Delaware Bay.
The chinook, which in part originates the Alberta clipper, usually brings relatively warm weather (often approaching Template:Cvt in the depths of winter) to southern Alberta itself, and the term is therefore not used in Alberta.
EffectsEdit
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 Template:Cvt in as little as 10 to 12 hours. Often, the storms bring biting winds with them, only increasing the effect of the lower temperatures. Winds in advance of and during an Alberta clipper are frequently as high as Template:Cvt. These conditions would cause wind chill values to drop into the Template:Cvt range across the upper Midwest and Great Lakes.<ref name="Islandnet">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
Snowfall amounts with these systems tend to be small (on the order of Template:Cvt), as the relative lack of moisture and quick movement inhibit substantial snowfall totals. However, several factors could combine to produce higher snow accumulations (Template:Cvt 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.<ref name="Islandnet"/>
Occasionally the clippers, when reaching the upper Atlantic seaboard (usually north of Delaware), "bomb out" and can cause severe winter weather along the coast from Boston northward as Atlantic moisture is tapped. Snowfall amounts can approach Template:Cvt or more when this happens. However, typically, Alberta clippers are not large snow producers south of Boston.
During the winter, Alberta clippers can occur somewhat frequently, with system intervals on the order of two to four days common during active periods.
See alsoEdit
ReferencesEdit
Further readingEdit
External linksEdit
- Extratropical Lows: Clippers—University of Illinois at Urbana-Champaign, Meteorology Department