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. 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.
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. 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 jet stream, sending the storm barreling into central and eastern areas of North America.
Ironically, the chinook which in part originates the Alberta clipper usually brings relatively warm weather (often approaching 10C/50F in the depths of winter) to southern Alberta itself, and the term is therefore not used in Alberta.