A big winter storm is the atmosphere's attempt to redistribute heat energy moreevenly through the atmosphere. This is accomplished through large-scalecirculations (storms) that move cold air masses south and warm air massesnorth. The motion within a storm is three-dimensional, and the air that isascending is what produces large areas of precipitation.The term "wintry mix" refers to a combination of snow, sleet and freezing rain.
This variety of precipitation occurs when mild, moist air is rising up and overa wedge of cold air. Typically, this type of storm occurs as a sequence: Firstit snows, then there is a transition to sleet and freezing rain. In the end,the storm may wind up as plainFreezing rain occurs when raindrops freeze upon impact with the ground, trees,power lines and other cold surfaces. This happens when there is a mild layer ofair at a few thousand feet, while the air at the ground is still belowfreezing.
Sleet, on the other hand, occurs when the cold air at the ground is somewhatdeeper and the raindrops freeze before impact. In regards to travel, freezingrain is by far the more treacherous of the two.
Story by AccuWeather.com Senior Meteorologist John Kocet.
