Winter Weather Climatology
Winter storms can affect all areas of the United States, including the Deep South and the deserts of the Southwest. They also come in various sizes and are created by different combinations of atmospheric conditions and the local geography.
The general availability of both cold and warm air in the troposphere makes winter storms in middle latitudes a common occurrence in several regions around the country.
Two general weather conditions associated with winter are overrunning and upsloping.
Overrunning occurs when moist, warmer air is directed up and over a mass of colder air at the surface of the earth. The warm air cools as it rises, and its moisture condenses into precipitation-producing clouds.
In an upslope flow, air rises and cools as it is forced to ascend to higher terrain. It then condenses and forms into clouds if it is cooled to its dew point.