Winter-weary Americans were hit with another massive storm Tuesday which was expected to dump as much as a foot of snow and a dangerous mix of freezing rain and sleet on a huge swath of the United States.

People barely had time to finish clearing their driveways from the last big storm when the warnings came that another whopper was headed their way.

"A winter storm moving across the Midwest eastward through the Northeast will be followed by another plunge of Arctic air into the center of the country," the national weather service warned.

"The southwestern US will be the only area of the country spared from this Arctic blast."

Temperatures have already been so unusually cold this winter that supplies of propane -- which many homes and livestock farmers use for heating -- are dangerously low. Seven Midwestern governors sent President Barack Obama a letter Tuesday asking for help in relieving the shortages.

The central plains states of Kansas, Missouri and Nebraska were the first to be hit by this latest storm on Tuesday. By the evening commute, freezing rain had already knocked down power lines and snarled traffic as far east as Arkansas and Tennessee.

The storm was set to reach the east coast on Wednesday, when a low pressure system would bring warmer air that would turn the heavy snow into freezing rain in the Appalachians and southern New England. The weather service warned it could also cause flash flooding.

Schools across the region sent children home early or cancelled classes completely and scores of government offices and businesses were also closed.

Authorities issued please to motorists to stay off the roads, citing the risk of traffic accidents.

The Kansas Highway Patrol filled its Twitter feed with photos of trucks, busses and cars which had slid off snow-covered roads.