GBDNA / Alberta Clippers

< Border Trackers | Guide to Baroclinic Disturbances
U N D E R   C O N S T R U C T I O N

Common Storm Tracks of Midlatitude Cyclones
Alberta Clippers

Region Of Cyclogenesis: Alberta or Montana

Lowest Range Of Central Pressure At Surface: 982 to 1018MB

Forward Speed: Rapid; cross-continent sequence within 72 hours

Season of Occurrence: November 15 to April 1

500MB Structure: Shortwave in conjunction with vortex over Hudson Bay or James Bay

Associated Sensible Weather: One of the most misunderstood of all storm tracks. A true Alberta Clipper exhibits a rapid and parabolic motion. Accompanied by sudden deepening and intense winds at most levels of the atmosphere to the right of the Rocky Mountains. While moisture may be lacking, a typical clipper can generate ground blizzards with rapid advection of cold air along and in the wake of its passage. Cold and overrunning sector snowfall is usually about 1 - 3 inches, although maximum amounts of 8 inches are not unheard of. Unlike many mid-latitude cyclones in North America, the heaviest snow is generally seen along and just north of the path of maximum vorticity at 500MB.

Some systems of the Clipper type may produce sleet and freezing rain in the overrunning sector, especially those storms that take the traditional track through MO into S QC. Prolonged wedge episodes may result with anywhere from 1 to 6 hours of icing or glazing in parts of Appalachia and the Interstate 95 corridor above Washington DC.

Variations In The Storm Track: There can be a wide range of deviations from the traditional Alberta Clipper trajectory. Some clippers imitate the Border Tracker type after formation. Another subfamily may take a further south and east path, with potential for center jumping or secondary cyclogenesis in the vicinity of the VA Tidewater. This option may present risks of moderate or heavy snowfall to the Mid-Atlantic and New England states, using the Atlantic Ocean as a moisture source while cA values infiltrate the northwest quadrant of the low. All disturbances of the Alberta Clipper family have two things in common: the lows are produced by leeside redevelopment and the upper level component is steered in some way by a cPk, cA, or cAk gyre over ON, MB, or Hudson Bay.

Classic Case: Occasionally the southern variant of the Alberta Clipper can produce near-blizzard conditions with heavy snows. Witness the January 22 - 24 2005 storm that formed over S AB before taking an east-southeast path into the VA Capes.

As for a “traditional” Clipper track, the January 28 1977 blizzard affecting the lower Great Lakes stands out as an example of this type that can trigger extreme lake-effect and lake-related snowfall, escorted by bitter cold air from northern Canada.

"A Guide to Baroclinic Disturbances" is © 2007 by Larry Cosgrove.
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