US winter storm to bring coldest Christmas in decades

A major winter storm sweeping the US this week may bring the coldest Christmas in four decades to parts of the country, say forecasters.

The "once-in-a-generation" cold snap - which began in the Pacific Northwest on Tuesday, before churning east - will become a "bomb cyclone" by Friday.

More than 90 million people are under winter weather alerts across 37 states.

About 80% of the nation is set to experience sub-zero temperatures, including places as far south as Texas.