Winter Storms - One name for many forms of extreme weather.They may differ in name and form, but they are all disruptive.
The topic is a large and complex one. Some types of winter storm occurregularly each season, sometimes more than once, and have beengiven their own names - Alberta Clipper, Nor'easter, Panhandle Hook. Others, just as severe, are not so romantically named.
But rather than describe each type of storm, let's look for some common ground. When you want to find out more about the events which affect you most often, wander on over to
The Weather Doctor's
A Few Basic Facts and Principles
I'm sorry to do this to you, but most winter storms have a
number of features in common, so let's set the scene.
But first, let's clear up the term "storm". For our purposes, a
storm is any disturbed state of the atmosphere affecting the
earth's surface, accompanied by unpleasant or destructive
weather. In scale a storm ranges from an individual
thunderstorm to hurricanes or even larger extra-tropical
depressions. Low pressure, usually as an enclosed low,
is associated with many of them.
Winter storms fit in towards the larger end of the scale,
particularly as far as the area affected is concerned.
Not the best of definitions I guess, but the overall complexity
of storms prevents a simple definition
So let's set the stage for storm formation. Here are some basic
weather and climate fundamentals.
The atmosphere is composed of Air Masses which vary in
temperature and the amount of water vapour they contain. They
are usually fixed in position during a particular season,
although they expand and contract, and some may disappear
altogether as the seasons change.
In winter in North America, five air masses are present,
and four of them interact to control storm development. They are
The maritime tropical (mT) warm moist air mass centred over
the southern Atlantic and Gulf of Mexico.
A maritime polar (mP) air mass in the northern Atlantic,
consisting of cool moist air.
Another mP mass in the northern Pacific.
And between the two maritime polar air masses, a continental
polar mass (cP) - cold and dry. Sitting to the north of this air
mass is an even colder continental Arctic body (cA), which has
little effect on storm formation.
Air masses can expand in different directions, taking the
place of part of the neighbouring air mass.
The boundaries between air masses are narrow zones where
temperature and/or water vapour content may change rapidly. These
contacts are called fronts. If the colder air mass is moving
into the warmer it is a cold front, and a warm front is the
In winter, the most important boundary is the Polar Front.
In North America it occurs at the southern contact between the
continental polar airmass and some form of the maritime tropical
air mass. When conditions are stable it runs east west across
most of continental North America.
Following this boundary are the fast, high altitude winds
of the polar Jet Stream (there is also a subtropical jet
stream which barely concerns us here), blowing from west to east
somewhere between 7.5 and 10.5km (25,000 to 35,000 ft). By
definition the winds in a jet stream blow at 57mph (92kph),
but faster zones, called jet streaks, are common.
During winter, prolonged cooling of the polar and arctic
continental air masses produces a large and growing mass of
dense cold air - a high pressure zone. Eventually, as a
means of equalizing temperature and pressure, this cold
dry air will spill out southwards, forming a wedge,
usually over the centre of the continent. Naturally the Polar
Front will follow the boundary between the air masses, and so
will the jet stream
The jet stream therefore develops a large loop as it tracks
the polar front south around the cold air outburst and back
Jet streaks anywhere along the path of the jet stream
are likely to cause disturbances to the flow of air around them.
These disruptions often take the form of closed low pressure
cells (cyclones or depressions), from which winter storms form.
Many winter storms are propelled and guided by the jet stream,
but can move in any direction, although west to east is favoured.
The storm's final path will be affected by coriolis effect,
which will deflect it to the right of its direction of movement
in the northern hemisphere. The storm may also be
slowed or blocked by other systems in front of it.
Storm formation is complex enough even within this scenario (and
this is by no means the full story), and the factors listed above
also apply reasonably well to eastern Europe. But now let's add
in the effect of the Rocky Mountain chain.
Many of the surface disturbances develop over the northern
Pacific and move east to the North American mainland. But when
they hit the Rockies, they are forced up and around, losing much
of their moisture content and energy as rain and snow is dumped.
Many retain enough of their character to reform on the eastern side
of the mountains, and start all over again as a significant storm.
(Europe has no significant chains of north - south mountains to
interrupt the movement of weather systems.)
So during winter we have a group of lows forming in the northern
Pacific, reforming over or past the Rockies, and moving on to
affect the northern and northeastern USA and Canada.
A second group of winter storms forms in the Gulf of Mexico and western
Atlantic.These storms track up the eastern side of the USA,
varying from inland of the Appalachians to 200-300 miles
(300-500km) out to sea.
Of course these two groups can find many ways to interact, and
that is often when things get really interesting.
Winter Storms with a Western Origin
Eastern Pacific storms have two sources. Many of them originate
in the relatively warm maritime polar airmass, particularly
in the Gulf of Alaska. High mountains around the Gulf restrict
these Gulf of Alaska Lows, causing them to move off to the
south to ultimately cross the coast anywhere between Canada
and California. Perhaps helped along by the jetstream, they
are forced to rise over the Rockies, dumping their contained
moisture as they cool, as either rain or snow.
The second source is more a means of moving weather than a
storm in itself. It is associated with the subtropical jetstream
and because it arrives from the direction of Hawaii, is called
the Pineapple Express. This fast moving stream of warm, very
moist air can meet the west coast anywhere from southern
Canada to California, and is capable causing very high
rainfall and snow as it rises over the Rockies.
Mix the Pineapple Express with a Gulf of Alaska Low and it's
time to dust off the record books.
In crossing the Rockies these storms have lost most of their
moisture, but still have the capacity to reform. Although this
can happen anywhere, there are two main centres for regeneration
- Alberta and Colorado.
Gulf of Alaska Lows form rapidly and follow each other quickly,
and so do Alberta Clippers. The name comes from the fastest of
the nineteenth century sailing ships. They form around the
Alberta plains and head off along the polar front, generally
passing into Montana or North Dakota before heading east
towards the Great Lakes and New England and the Maritime
Provinces of Canada.
Because they have lost most of their moisture and have little
access to more, they are rarely responsible for heavy rain or
snow - 2 to 4 inches on the northern side of their path is
about the norm. They are usually followed by very cold
northerly winds, and their rapid generation can result in some
long spells of rather miserable weather.
Alberta Clippers can result in heavy Lake Effect snows on the
lee sides of the Great Lakes, and although they are otherwise
not usually responsible for much new snow, their strong winds
can cause blizzards as previously fallen snow is picked up
and moved around.
Colorado Lows and Panhandle Hooks
Pacific storms often reform around Colorado. When the jetstream
is in its normal position and travelling east around the
Canadian border, these and other winter storms forming in the
southern Rockies will normally track east, pick up some
moisture from the Gulf of Mexico, and cause a little rain and
But when the jetstream loops south, the Colorado Lows and
the related Texas Panhandle Hooks head off to the north or
northeast and have the potential to cause serious problems.
They follow the polar front and jetstream north, picking
up plenty of moisture from the gulf maritime air to the east.
Circulation around the low pressure center brings strong
northerlies, including the Blue Norther of southern states,
with potentially large snowfalls to the west of the storm's
path. Characteristic paths for these large winter storms include the
Ohio valley, and strong winds and large snowfalls for the
Chicago - Great Lakes area are possible.
These storms are also likely to move on to New England and
the Canadian Maritime Provinces.
East Coast Storms
A large group of winter storms affecting the east, and particularly
northeast Atlantic coast of the USA and Canada are known as
Nor'easters, after the direction of the winds bringing
the worst of the rain, strong winds, and snow.
In keeping with the rule that nothing is simple, Nor'easters
can form in several ways, have a wide range of paths ranging
from inland to well offshore, and have the potential to
virtually explode into devastating events ("The Perfect
One group of storms forms in the Gulf of Mexico or nearby
western Atlantic. Depending on source and location of
mid continent highs or jetstreams, these storms can move
along the western margin of the Appalachians, along the
coastal plain, or anywhere within a few hundred miles off
Typical of winter storms, snow is likely to fall to the
left of the storm's track, with rain more likely to the
right. Storms moving north over the ocean will usually
produce snow in coastal areas (to their left) as they
are continually picking up moisture from the relatively
warm sea surface, often including the Gulf Stream. Other
storms form off Cape Hatteras and move in the same way.
Some Nor'easters, particularly those intensifying off New
England or eastern Canada, may be the remnants of Alberta
Clippers, Colorado Lows or Panhandle Hooks. Normally these
systems will move off rapidly to the east to be seen no
more, but other scenarios are possible.
If, for example, a Colorado Low runs into a Nor'easter
moving north along the coast, or even an extra-tropical
low moving in from further out in the Atlantic, an
extremely powerful storm can grow very rapidly. Winter storms
such as these are responsible for huge dumps of snow
from New York northward, hurricane force winds, and
huge seas accompanied by storm surges. These weather
bombs or bomb cyclones can form in other ways, but
their characteristic is rapid development of a very
Winter storms are a great field for observation and study
by the owner of a home weather station.
For a start, no matter where you live in North America, you
would expect to see several reasonable winter storms each year
between the beginning of fall and the end of spring, whereas
a hurricane or severe thunderstorm may be rare or nonexistent
in many regions.
Secondly, most winter storms take a while to build up, pass through
and decline, giving plenty of time to assemble records.
Thirdly, with the sort of weather likely in most winter storms
you probably will be staying home with enough time on your hands
to indulge in a bit of weather study.
And finally, depending on where you are in relation to the storm's
path, the sequence of weather and trends in observed data may be
quite different even though the type of storm is the same.
The topic of Winter Storms covers a wide variety of weather
patterns and types of threatening, if not
While many websites cover warmer weather events like hurricanes
and tornadoes, winter weather doesn't attract quite the same
The Weather Doctor
provides a large number of
informative and entertaining articles on many aspects of
winter weather. For an overall, concise view work your
way through the weather section of
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