London Telegraph 
Jan 30, 2011
Meteorologists say a freak weather phenomenon over the Arctic is responsible for the storms which have dumped record amounts of snow on the United States East Coast this winter.
The phenomenon, known as the North Atlantic Oscillation, is pushing frigid winds from the North Pole across the Atlantic, where they are colliding with the warm, moisture-laden air over the southern US. Jet streams, a belt of winds aloft at about 18,000 feet, are then carrying the cold air north-west, where the moisture is falling as snow.
In normal winters, the air mass above the Arctic is surrounded by a circular vortex of wind currents – a kind of fence that keeps in the frigid polar air. This condition, which meteorologists call the North Atlantic Oscillation’s Positive Phase, ensures both sides of the Atlantic have relatively mild winters.
But for reasons experts do not fully understand, the North Atlantic Oscillation sometimes switches to a Negative Phase. High pressure develops over the Arctic, forcing cold air south into North America and Eurasia. Jeff Masters, a meteorologist, explains that the phenomenon is a little like “leaving the refrigerator door ajar – the refrigerator warms up, but all of the cold air spills out into the house.”