Extreme winter weather conditions,including crippling snow and ice storms and deadly cold waves,affect parts of the United States every winter.

To anticipate these events, forecasters look for certain large-scale weather patterns that can sometimes signal the arrivalof extreme winter weather conditions.

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Here are a few of the weather patterns to watch for this winter.

1.) East Coast Snowstorm Pattern

When examining the potential for a blockbuster East Coast winter storm,meteorologists monitor an index called the North Atlantic Oscillation (NAO). The index has a positiveand negative phase,and as its name implies, it oscillates between those phases to various degrees over periods of days or weeks.

To be clear, the NAO is just one factor in the grand scheme of forecasting, but when it slips into adeeply negative state, East Coast snow-loving weather geeks begin to salivate.

The area of blocking high pressure near Greenland locks in a southward dip in the jet stream across the eastern states when the NAO is in its negative phase. This leads to persistent cold temperatures and the potential for East Coast snowstorms.

At a Glance

There are several weather patterns that capture the full attention of meteorologists in winter.These weather patterns can result in major snow and ice storms and also usher in the most frigid air of the season.

During a negative phase of theNAOin the colder months of the year, the jet stream dips southward over the eastern United States where it may lock in for a lengthy period of time. This is due towhat meteorologists call atmospheric blocking. In the case of a negative NAO, the blockoften takes the form of a strong bubble of high pressure near Greenland.

Depending on the orientation of that jet stream dip, and the potency and evolution of disturbances traversing through it, one or more major snowstorms can spinup and impact some part of the East Coast or Atlantic Canada in a negative NAO pattern.

This is because theblocking alluded to in the NAO negative phase allows intensifying low-pressure systems to crawl up near or just off the Eastern Seaboard rather than scooting harmlessly out to sea.

A recentexample of this occurred in mid-January 2016 when the NAO slipped into a . Coincidingwith the plummeting NAO index was, which buried the mid-Atlantic and Northeast with record-breaking snow totals that were measured in feet.

All of this being said, the Northeast can still see significant snowstorms even without a negative NAO.

2.) The Arctic Express

Forecasters look to Alaska, Canada's Arctic region and even Siberia for signs of bitterly cold air masses building during the heart of winter.

Highlighted by the ring and shaded pink and purple is an arctic air mass that descended southward into the U.S. from near the North Pole during February 2016.

Arctic air masses from those source regions don't alwayspour south of the Canadian border when they develop, but when they do, the continental U.S. usually experiences its most extreme cold outbreaks of the winter.

The frigid air from those regions is typically dislodged when the jet stream builds northward over western North America. As a result, a southward plunge of the jet stream sweeps across the central and eastern United States, ushering in the shivering, and in some cases, subzero temperatures.

The most extreme and long-lasting cold weather patterns in the central and eastern states coincide with the aforementioned negative phase of the NAO.

When the NAO is negative, the same atmospheric blocking described in the section above keeps a pipeline of arctic airentrenched east of the Rockies. This can lead to bone-chilling temperatures that remain below average for more than a week.

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3.) Long-Lasting West Coast Atmospheric Rivers

One of the most extreme weather patterns for the West Coast during winter is an atmospheric river.

Cabins buried by snow at Mammoth Lakes, California, in January 2017. (Marc Monney/Instagram)

An atmospheric river is a narrow plume of moisture extending into the tropics or subtropics that Pacific storms systems can tap into as they plow inland. The atmospheric river provides extra juice to storm systems taking aim at the coasts of Washington, Oregon and/or California. Sometimesthe extra moisture can be overwhelming, with heavy rain causing flooding while feet of snow pile up in higher terrain.

Fortunately, atmospheric river events can typically be forecast beforehandthanks to satellite data providing evidence of their development. Computer models then use the satellite-based information to give forecasters information on the magnitude and duration of a particular event.

One of the happened in January 2017.

More than 10 feet of snow fell in the higher elevations of the Lake Tahoe region during a seven-day period. In the lower elevations, flooding rainfall affected parts of California and western Nevada. Somelocations in California saw more than twofeet of rain.

with additional flooding in February 2017.

4.) Expansive Ice Storms

Major ice storms are among the most high-impact winter weather events. They'redestructive to trees and power lines andcan bringtravel to a standstill.

Some of the most expansiveice storms east of the Rockies develop in aweather patterneasily recognized by meteorologists.

Typically this setup features arctic air that isfed by a northerly wind near the earth's surface. This cold air source is then overrun by mild, moist air ushered in on southerly winds from the Gulf of Mexico.

The jet stream sends disturbances over the top of this battleground between cold and mild air, adding additional lift to the atmosphere. The result is a large swath of precipitation that can extend for hundreds of miles in a west-to-east fashion.

Depending on the intensity and longevity of the that develops, impacts can range from nuisance to crippling in any given location.

An example of a majorice storm of this type occurred in January 2009. Along swath of states fromsaw at least a quarter inch of icing, and some locations saw destructive accumulations of an inch or more.

Particularly hard hit were Kentucky and northern Arkansas.For Kentucky, it caused the largest power outage in the state's history with 609,000 homes and businesses in the dark.

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Damage in northern Arkansas from the 2009 ice storm. (weather.com photos user patpie)

5.) Lake-Effect Snow Machine

Lake-effect snow downwind of the Great Lakes is a common occurrence from late-fall through the heart of winter.

The ideal jet-stream pattern for generating heavy lake-effect snow.

Sometimes these events are short-lived, while others can pelt the same areas for days at a time.

Meteorologists take extra notice when a familiar setup forheavy lake-effect snow is projected by forecast-guidance tools.The patternfeatures a sharp, persistent southward plunge of the jet stream anchored over the eastern U.S. by a gyre of low pressure over or near Canada's Hudson Bay.

In this pattern, repeated rounds of cold air spill over the Great Lakes, manufacturing bands of heavy lake-effect snow that can persist for several days, in spots.

Snowfall amounts measured in feet are typical during lake-effect snow events featuring this long-lived setup, particularly east of Lakes Erie and Ontario.

One of the most extreme situations occurred over a 10-day period from Feb. 3-12, 2007,when an incredible 141 inches of snow was measured in Redfield, New York, about 50 miles northeast of Syracuse.

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Left: A giant snow pile is left in the wake of the February 2007 lake-effect snowstorm. Right: Snowfall totals from the Feb. 3-12, 2007 lake-effect snowstorm in the Lake Ontario snowbelt. (AP/NWS-Buffalo)