Freezing US Set For Dramatic Temperature Rise

The US was in the grip of a cold snap on Thursday and Friday, with snow on the ground in 49 out of 50 states, including Hawaii.
The only state without snow was Florida. Oklahoma had experienced its snowiest month in 100 years.
However, a dramatic increase in temperature is forecast for this weekend; the mercury set to rise by as much as a 100 degrees (farenheit) in some places.
So what is responsible for this dramatic change?
The jet stream, a fast-moving ribbon of air high up in the atmosphere that marks the boundary between cold and warm air, has been further south than usual, with cold air to its north and warm air to its south.
The jet stream is moving northwards this weekend, allowing southern and central states to warm up.