A Clipper storm is a fast-moving, low-pressure system that develops in the interior of North America, frequently affecting the midwestern and eastern portions of the continent during colder months. Often called an “Alberta Clipper,” this storm originates near the Canadian province of Alberta. It is characterized by rapid speed and low moisture content, differentiating it from slower, heavier winter systems. The storm’s track generally takes it southeastward across the continent, bringing a quick burst of wintry weather.
The Meteorological Process of Formation
The genesis of a Clipper storm is a process known as lee cyclogenesis, which occurs on the downwind side of a large mountain range. This process begins when a parent low-pressure system moves eastward from the Pacific Ocean and encounters the Canadian Rocky Mountains. As the air mass crosses the mountains, it loses much of its moisture on the windward side through precipitation. Upon descending the eastern slopes of the Rockies, the air warms and dries adiabatically, creating a low-pressure trough near Alberta.
The development of the Clipper cyclone is driven by upper-level atmospheric dynamics, specifically the presence of a strong upper-level trough. This setup causes vortex stretching and enhanced baroclinicity, leading to the rapid formation of a surface low. Once the low-pressure center forms, it becomes quickly entangled with the Polar Jet Stream, which usually flows from the northwest to the southeast during winter. The powerful, high-altitude winds of the jet stream steer the system rapidly across the Canadian Prairies and into the United States. Because of this speed, the system does not have time to deepen or draw in significant low-level moisture.
Defining Characteristics and Naming
The system’s speed is its defining characteristic and the origin of its common name. The “Clipper” term references the swift sailing ships of the 19th century. These storms often travel across the entire continent in two to three days. Clipper storms are generally considered weak cyclones compared to other winter systems because they feature a relatively small pressure gradient.
Their cold, dry nature is derived from the continental polar or arctic air mass pulled in from northern Canada. This low moisture content causes the storm to produce light, dry, and fluffy snow, often referred to as “powder.” Snowfall totals are modest, usually ranging from a dusting to about three inches for most areas. The fast movement contributes to lower accumulation totals because the storm does not linger long enough to drop large amounts of snow. The snow that does fall is easily lofted and blown around by the associated strong winds.
Typical Tracking and Associated Weather
The typical track for a Clipper storm starts in Alberta and proceeds eastward across Saskatchewan and Manitoba. It then sweeps southeastward across the Upper Midwest of the United States, traversing the Dakotas, Minnesota, and the Great Lakes region. The low-pressure system continues its journey, eventually moving across the Northeast and off the coast into the North Atlantic.
The weather associated with a Clipper includes gusty winds and a sharp drop in temperature. Winds frequently reach speeds of 35 to 45 miles per hour, causing significant blowing and drifting of the light snowfall. The cold front that follows the storm can cause temperatures to plummet by as much as 30 degrees Fahrenheit in a short period. This rapid temperature decrease can lead to hazardous conditions, including the potential for a flash freeze on wet road surfaces.
While the snowfall is light, the strong winds and reduced visibility from blowing snow can lead to localized blizzard conditions, especially in open areas. As the cold air mass moves over the warmer waters of the Great Lakes, a Clipper can enhance lake-effect snow downwind of the lakes. Clipper storms contrast with major winter systems, such as Nor’easters, which are slower and draw substantial moisture from the Atlantic Ocean to produce heavy, wet snowfall. The Clipper is a frequent winter visitor, delivering a quick shot of cold air and snow that clears out quickly.