The United States is bracing for a frigid winter as a significant polar vortex makes its initial descent across the nation, meteorologists caution. This chilling weather pattern marks just the start of an extended cold spell.

Recent weather forecasts indicate that the Midwest and Northeast are currently experiencing the first wave of an arctic “outbreak.” This will likely lead to further incursions of icy air migrating south from Canada over the coming three weeks.

States ranging from Montana to Maine are anticipated to experience temperatures that are 10 to 15 degrees Fahrenheit below the historical norms for early to mid-December. Additionally, there will be multiple opportunities for snow squalls to develop.

This initial polar vortex occurrence is expected to usher in the first substantial snowfall of the season in regions including upstate New York, Vermont, New Hampshire, Maine, and parts of the northern Mid-Atlantic states by Tuesday.

According to meteorologists, the approaching Nor’easter is predicted to deliver three to five inches of snow at lower elevations, while higher terrains such as the Adirondacks, Green Mountains, and White Mountains could see snowfall totals of at least five to eight inches.

The National Weather Service (NWS) has issued winter storm warnings and winter weather advisories throughout the Northeast and parts of the Midwest, from Maine to central Kentucky.

A state of emergency has already been declared in New Jersey, where Governor Phil Murphy warned that at least five northern counties should expect snow, sleet, freezing rain and potential power outages on Tuesday.

Meanwhile, the Federal Aviation Administration (FAA) has already begun issuing ground delays due to poor weather at airports in New York and Washington, while over a dozen hubs throughout the US fight to keep their runways free of dangerous ice.

Winter storm warnings have been issued in New England on Tuesday

A Nor’easter is set to bring several inches of snow to the Northeast, just days after Americans in Illinois were hit with a holiday weekend snow storm (Pictured)

This frigid forecast is expected to last all week throughout the US as cold air from Canada and Greenland plunges south because of a weakening in the Earth’s polar vortex.

The polar vortex is like a giant, spinning whirlpool of cold air high up in the atmosphere above the North Pole, normally held in place by strong winds that act as a barrier, keeping the extreme cold locked away from the US.

However, strong storms and high-pressure systems in the lower atmosphere have sent ripples of warmer air upward that knocked this vortex off balance, allowing the icy Arctic air to dip farther south and blanket the US.

That cold air from the north has now collided with warm air from the Gulf Coast, creating a mix of rain and snow in the South, and heavy snow everywhere north of Missouri.

Temperatures are expected to remain around the freezing point throughout the rest of the week, with the polar vortex projected to descend all the way to the South on Wednesday and Thursday, reaching Oklahoma, Arkansas, Missouri, and Tennessee.

AccuWeather has warned that parts of at least 20 states may see temperatures drop up to 20 degrees below historical averages for the beginning of December.

In Midwest states such as Iowa, Minnesota, Illinois, and Wisconsin, forecasters have said that Thursday could see the thermometer fall well below zero, hitting -10 in some spots, which may break records throughout the region which have stood for decades.

On Friday, record-low temperatures in the teens and 20s have also been forecasted for New York, Chicago, Indianapolis, and Baltimore.

Cold air moving south due to an unstable polar vortex is expected to continue creating record-low temperatures for another two weeks

Several states in the upper Midwest are predicted to set record-low temperatures for early December on Thursday

AccuWeather has predicted not one, but three ‘polar vortex episodes’ before winter officially begins on December 21.

These big surges of stratospheric cold air crashing down to ground level are what lead to record-low temperatures.

The first episode kicked off this week, bringing the Nor’easter snow event and Thursday’s arctic plunge, but it won’t fizzle quickly.

Instead, it could stretch into the next two weeks due to the weather phenomenon known as La Niña teaming up with the unstable polar vortex to create a ‘stuck’ pattern, where cold air pools over the eastern US and doesn’t leave.

Climatologist Judah Cohen, a research scientist at MIT, told USA Today: ‘My thinking is that the cold the first week of December is the appetizer and the main course will be in mid-December.’

Cohen claimed that his computer model has forecasted ‘that the most expansive region of most likely extreme cold on Earth stretches from the Canadian Plains to the US East Coast in the third week of December.’

Until the first weekend of winter in late December, the Northeast and Midwest should continue to expect frequent light-to-moderate snow storms, with highs only reaching the 20s and lows in the teens or single digits. Lake-effect snow could pile up several feet high near the Great Lakes.

In the South and Great Plains, unusually chilly conditions threaten to drop highs into the 40s, down from their usual averages in the 50s and 60s.

Morning frost and freeze risks could kill crops and damage pipes as far south as Texas and the Carolinas.