At least three people have died as a powerful winter storm moves east across the US, spawning tornadoes in southern states and coating others in snow. A young boy and his mother were killed in Louisiana when their home was destroyed by a tornado. The huge storm also brought blizzard-like conditions to the Midwest, with roads and schools closed and some areas reporting 4ft (1.2m) of snow. Around 3,300 flights have been delayed and over 150 more cancelled. Some 500,000 people across four states - Nebraska, Wyoming, South Dakota and Minnesota - are under blizzard warnings, with powerful winds and