Forecasters in the US have declared a major winter storm this week, bringing the coldest Christmas in 4 decades to parts of the country.

According to reports the “once-in-a-generation” cold snap which began in the Pacific Northwest will become a “bomb cyclone” by Friday.

More than 90 million people are under winter weather alerts across 37states as about 80% of the nation is set to experience sub-zero temperatures, including places as far south as Texas.

Named Winter Storm Elliot by the Weather Channel, the arctic blast is expected to deliver the coldest Christmas to the Midwest since the late 1980s.