Snow, sleet and freezing temperatures are forecast for the south, midwest and east coast over the weekend

The dangerous monster storm threatening half of the US was on Friday bearing down, with 16 states and Washington DC already declaring emergencies and areas typically unused to prolonged Arctic temperatures bracing for power failures and supply shortages.

At least 230 million people are likely to be affected by the huge winter weather system as it forms in parts of the Rocky Mountains and Great Plains and surges across southern and midwestern areas from Friday, blowing up the east coast on Saturday and as far north as Maine by Sunday.