'Life-threatening' winter storm to hit US with snow, ice and 'dangerously' cold temperatures

A major winter storm is set to sweep the United States this weekend, bringing with it snow, sleet, ice and sub-zero temperatures from the Arizona-New Mexico border to upstate New York.

What is it? A winter storm is defined as a combination of heavy snow, blowing snow and/or dangerous wind chills, according to the NOAA's National Severe Storms Laboratory, which also describes it as "life-threatening". The approaching storm is due to an area of low pressure moving up from the Gulf of Mexico (bringing lots of moisture) and meeting extremely cold Arctic air plunging south from Canada.

The winter storm set to hit the US comes with warnings of ice. An ice storm is one which results in the accumulation of at least a quarter of an inch of ice on exposed surfaces - creating hazardous driving and walking conditions and the threat of downed power lines and trees.

Where is it heading? The National Weather Service has warned communities the "significant, long-duration winter storm" will bring "widespread heavy snow, sleet and freezing rain from the Southern Rockies to New England" - lasting from Friday until Monday, and to prepare for "bitterly cold temperatures and dangerously cold wind chills". The storm is expected to bring a crippling ice storm from Texas through parts of the South, potentially around 30cm (12ins) of snow from Oklahoma through Washington DC, New York and Boston.

Then a final punch of bitterly cold air could plunge temperatures to -46C (-50F) in parts of Minnesota and North Dakota. Forecasters are warning the damage, especially in areas hit by heavy snowfall and ice, could rival a hurricane.

"The storm will cause significant to locally catastrophic ice accumulations with the potential for long-duration power outages, extensive tree damage, and extremely dangerous or impassable travel conditions," the NWS said. "In the wake of the storm, communities from the Southern Plains to the Northeast will contend with bitterly cold temperatures and dangerously cold wind chills.

This will cause prolonged hazardous travel and infrastructure impacts." Millions braced for 'catastrophic' winter storm About 160 million people - nearly half the population of the United States - are under a variety of watches, warnings and alerts. The alerts stretch from Arizona and Montana in the west to the Carolinas and Maine in the east.

So far, 12 states have declared states of emergency ahead of the winter storm. These include Texas, Georgia, South Carolina, North Carolina, Virginia, Maryland, Louisiana, Arkansas, Tennessee, Alabama, Mississippi and Missouri.

What has the federal response been? The Federal Emergency Management Agency (FEMA) has pre-positioned supplies and is deploying more than 200 call centre specialists across the country ahead of the winter storm, according to an agency document obtained by Sky's US partner network NBC News. The document said supplies and equipment include 250,000 meals, 400,000 litres of water, 30 generators and 12 shuttle drivers at Camp Minden, Louisiana.

A further 24 shuttle drivers are being deployed at distribution centres in Greencastle, Pennsylvania; 12 in Fort Worth, Texas; and 22 in Atlanta to quickly move commodities. A total of 28 search and rescue teams are also on standby.

FEMA's National Response Coordination Center and regional centres are activated. What have people been told to do? Residents have been advised to stay at home and off the roads and to prepare by stocking up on food and drink supplies.

"Items like flashlights, batteries, and battery back-ups can make all the difference," the North Carolina Department of Emergency Management said in a social media post. Items including mobile phone chargers, radios, winter clothing, blankets and a first-aid kit should also be added to households' emergency kits.

It warned people should never run a generator inside a house or garage to avoid carbon monoxide poisoning. The Georgia Emergency Management Agency said people should regularly check the weather forecast for any changes and gather emergency supplies for both their homes and cars, check smoke and carbon monoxide detectors, and refuel cars and heating sources.

It also said people should check in on neighbours and family, properly ventilate emergency heat sources, keep generators 20ft from homes and to be careful while shovelling snow and ice..