A bitterly cold Arctic air mass has caused temperatures to plummet across much of the northern hemisphere, where parts of the US, Canada and Siberia have recorded temperatures below minus 40C.
In the US, the powerful Arctic storm has placed more than 200mn people, about 60 per cent of the population, under weekend weather alerts with warnings of life-threatening wind chills, blizzards and ice storms.
The cold weather and hazard forecasts extend as far south as the US-Mexico border, the Gulf coast and Florida, where near-freezing temperatures are expected on Christmas Eve.
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