An Alberta Clipper is born in the Canadian province of Alberta. Itís one of the most significant synoptic-scale
winter weather phenomena affecting central North America. It occurs most frequently during December and January
and substantially less during October and March. Itís defined as; a very fast moving low-pressure
system, usually low in moisture content, originates in Alberta in the lee of the Canadian Rockies,
and then travels southeastwards. Often the Clipper travels through Winnipeg, Manitoba.
As a Pacific cyclone approaches the coast of British Columbia the lower-tropospheric wind flow crossing
the Rocky Mountains increases. A lee trough will develop as a result. Itíll remain stationary to the
lee slopes and broadens as air warmed by descent is advected eastward. The approaching upper-level
trough and its associated vorticity maximum produces cyclonic development within the lee trough. Once
a cold front overtakes the lee trough the cyclone begins to move away
from the lee of the Rocky Mountains.
Once the Alberta Clipper is formed east of the Rockies itíll sail southeastward into the Dakotas and
Minnesota, also effecting southern regions of Manitoba. It then steers across the Great Lakes, usually
just north of Lake Superior, before progressing eastward into southeastern Canada or the Northeastern
United States. Less that 10% of these storms track south of the Great Lakes. It usually moves
very rapidly, generally at 50-60 kilometers per hour.
This course keeps them hundreds of miles away from any moisture source, so typically they donít deposit
huge snowfalls. Alberta Clippers are generally regarded as rather small-scale systems, within the spectrum
of extra tropical cyclones. Lack of available moisture and rapid movement produce relatively low
precipitation amounts over a narrow band. However, several factors could combine to produce somewhat
impressive snowfall totals, 15 centimeters (6 inches) or more. These factors include; access to
more moisture, which could raise precipitation amounts, slower system movement, this increases
snowfall duration, and colder temperatures, this increases the snow to water ratio.
Other Precipitation Factors:
Alberta Clippers love La Nina years. La Nina means the Jet Stream dives south across the Great Lakes. That
can often mean areas surrounding the lakes are the only ones in the U.S. to see a white Christmas. The
Great Lakes southern and eastern shores often receive enhanced snowfall from Clippers during the winter
months from lake enhancement. Lake effect snow substantially increases snowfall totals. Also, if
conditions are favorable, an Alberta Clipper can rapidly intensify off the East Coast. Once the
storm taps the relatively warm moist air over the Atlantic Ocean, the storm sometimes spreads
heavy snow over New England and Southeastern Canada.
What the Alberta Clipper is most known for is itís strong, frigid winds. A mature Clipper can
sport winds of 65 kilometers per hour with gusts up to 95 (40 miles per hour with gusts up to 60). Itís
not uncommon for areas in the lee of the Rockies to sustain Chinooks as a Pacific Low approaches B.C.
Over Central and Eastern Northern America; the region between the cyclone and the often-intense
anticyclone trailing the Clipper experience the strongest winds. Enhanced winds associated
with a substantial pressure rise and fall, and a downward transport of high momentum air in
areas of strong cold air advection and low static stability produce strong winds. In the
wake of the Alberta Clipper strong winds usually follow. With recently fallen fresh snow, blizzard
conditions are common.
The push of the northwesterly jet stream tends to sail Alberta Clippers. Often these lows are followed by
bitter outbreaks of polar air, which can continue for days after the low has moved off. The effects of an
Alberta Clipper can be a drastic change in temperature. In the wake of the system the mercury could
plunge by 16 degrees Celsius (30F) in as little as 10 to 12 hours. Strong northerly winds and bitterly
cold temperatures leave behind dangerous wind-chills, ground
blizzards, and days of whiteout conditions.
Two variations of Alberta Clippers are Manitoba Maulers or Saskatchewan Screamers. These two types of systems
are far less common than Clippers, and even when they take place they are still often referred to as
Clippers. The main difference between the three is from which
Canadian province they begin their southward track.
The Weather Notebook by Dave Thurlow of the Mount Washington Observatory:
Wikipedia, the free Encyclopedia:
USA Today by Chad Palmer:
ďA synoptic-Climatology and Composite Analysis of The Alberta Clipper,Ē by Blaine Thomas and Jonathan
Martin with the Department of Atmospheric Oceanic Sciences University of Wisconsin-Madison