Meteorologists are using increasingly frightening language to warn Americans of a historic winter storm poised to pound a 2,000-mile-wide swathe of the United States.

The unusually large polar vortex, which has been named Fern, is set to be the biggest storm of the winter, weather experts at Accuweather said on Friday morning. 

The Weather Prediction Center similarly warned: 'Catastrophic impacts are expected where freezing rain amounts exceed a half inch'. 

Some 400 miles in the usually snowless South should fit that criteria, meteorologists said - creating conditions dangerous for travel and long-lasting power outages in parts of Louisiana, Arkansas, Mississippi, and Alabama.

The National Weather Service in Memphis, Tennessee, said to 'prepare to delay travel as roads and bridges are expected to be treacherous if not impossible this weekend.'

Parts of Mississippi will be hit even worse, the agency said. 

Forecasters there are warning of 'crippling ice accumulations' from ice and supercooled water droplets the will leave roads dangerously slick.

More than 15 million people are now under ice storm warnings in the South, and 230 million Americans overall.

'I think people are underestimating just how bad it’s going to be,' said former National Oceanic and Atmospheric Administration chief scientist Ryan Maue, now a private meteorologist. Conditions in the northeast, meanwhile, will be far worse. 

More than two dozen states from Texas to Maine will be affected in some way by the storm in some way.

A total of 12 states have declared states of emergency. 

'Potentially hundreds of thousands of people may go without electricity and heat for days,' AccuWeather Chief Meteorologist Jonathan Porter warned. 

The damage in areas hit by ice - and even in those that are not -  could rival a major hurricane, forecasters said.

A headline on the front page of Friday's Washington Post described the storm as a 'weekend tempest of ice.'

Storm chaser Kyle Cutten told Sky News the event will be a 'generational storm'.

'It’s going to cripple one third of the nation,' he warned. 'It’s something that becomes very life threatening when you have no heat and no service.'

He added that he hopes the fatality count is low. 

Residents in states like Arkansas, where an abnormal amount of winter weather is already being seen, 'are readying for the worst [and] hoping for the best,' Fox 16 reported. 

South Carolina's Post and Courier warned locals about downed powers lines roads set to be rendered 'impassable for days.'

The Weather Channel's Jim Cantore, who is tracking the storm from New York Cit, warned: 'The worst part of this storm will be the prolonged ICE ACCREATION [sic] followed by the COLD next week.'

Ice accretion is when when water droplets suspended in air freeze on objects they come in contact with, leaving roads with a slippery glaze.

'None of this will melt anytime soon. I hope you are ready for extended power outages,' he added.

On Friday afternoon,  the storm warning was expanded to include much of northern Georgia.

'Expect power outages and tree damage due to the ice. Travel could be impossible,' the National Weather Service said.

The warnings go into effect on Saturday at 1 p.m. ET. Snow is already falling across parts of western and central New York, after several inches were recorded in Texas this week.  

The most dangerous phase of a major winter storm is slated for later Saturday and early Sunday.

The alerts last through Monday 10 am ET. Experts said to expect up the three straight days of snowfall.