AnAlberta clipper, also known as anAlberta low,Alberta cyclone,Alberta lee cyclone,Canadian clipper, or simplyclipper, is a fast-movinglow-pressure system that originates in or near theCanadian province ofAlberta just east of theRocky Mountains and tracks east-southeastward across southern Canada and the northernUnited States to theNorth Atlantic Ocean.^[1][2][3]

Alberta clippers constitute a major winter-seasonstorm track forextratropical cyclones in theNorthern Hemisphere, tracking across the continent in 2–3 days while affecting weather in parts of thePrairies andcentral provinces ofCanada, as well as theUpper Midwest,Great Lakes, andNew England portions of the United States. They are associated with cold, dry continentalair masses and generate small-scale, short-lived weather events typically producing 8–15 cm (3.1–5.9 in) of snow in a 3-6 hour period. However, they can precipitate sudden temperature drops and sharp winds leading to localblizzard conditions, especially when interacting with moisture from the Great Lakes.^[4][5]

Alberta clippers take their name fromAlberta, the province from which they appear to descend, and fromclipper ships of the 19th century, one of the fastest ships of that time.^[3][6]

The term was coined in the late 1960s by Rheinhart Harms, a meteorologist at the U.S.National Weather Service Office inMilwaukee,Wisconsin, who noted the rapid speed of these snow-producing storms as they moved acrossthe Dakotas from Alberta towards the Great Lakes.^[7][8] Itscolloquial use spread among U.S. and Canadian weather forecasters in the early 1970s.^[9] It would enter 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 namesSaskatchewan screamer,Manitoba mauler orOntario scari-o.^{[3][10][11][12]}

A clipper originates when warm, moist winds from thePacific Ocean come into contact with the mountains in the provinces ofBritish Columbia and thenAlberta.^[5] The air travels down thelee side of the mountains, often forming achinook in Alberta, then develops into a storm over the Canadian prairies when it becomes entangled with the coldair mass that normally occupies that region in winter. The storm then moves east-southeast riding thejet stream, and passes off the upper Atlantic Coast, normally north ofDelaware Bay.

The chinook, which in part originates the Alberta clipper, usually brings relatively warm weather (often approaching 10 °C (50 °F) in the depths of winter) to southern Alberta itself, and the term is therefore not used in Alberta.

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 16 °C (29 °F) 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 56 to 72 km/h (35 to 45 mph). These conditions would causewind chill values to drop into the −30 to −45 °C (−22 to −49 °F) range across the upper Midwest and Great Lakes.^[13]

Snowfall amounts with these systems tend to be small (on the order of 2.5–7 cm [0.98–2.76 in]), as the relative lack of moisture and quick movement inhibit substantial snowfall totals. However, several factors could combine to produce higher snow accumulations (15 cm (5.9 in) 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 theGreat Lakes often receive enhanced snowfall from Alberta clippers during the winter, due to lake enhancement. Thelake-effect snow can add substantially to the overall snowfall total.^[13]

Occasionally the clippers, when reaching the upperAtlantic 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 150–300 mm (6–12 in) 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.

• Ground blizzard
• Panhandle hook
• Polar vortex
• Snow squall
• Wind chill

• Dunlop, Storm (2003).The Weather Identification Handbook: The Ultimate Guide for Weather Watchers. Guilford, Conn.: The Lyons Press.ISBN 9781585748570.OCLC 52307033.
• Williams, Jack (1997).The Weather Book (2nd rev. and updated ed.). New York: Vintage Books.ISBN 0-679-77665-6.OCLC 37820330.

• Extratropical Lows: Clippers—University of Illinois at Urbana-Champaign, Meteorology Department

• Blizzards in Canada
• Blizzards in the United States
• Extratropical cyclones
• Natural history of Alberta
• Natural history of Saskatchewan

• Articles with short description
• Short description is different from Wikidata