MIKE MOSS SAYS: Hannah, Fortunately, really intense ice storms are rather rare across the Southern U.S. but they certainly do occur from time to time and one reason they can be so destructive on occasion is the proximity of the Gulf of Mexico to the south and the Gulf Stream off the southeast coast, both of which can be sources of relatively warm, moisture-laden air that, when combined with the right patterns involving shallow layers of cold, dry air flowing into the region from the north and lifting mechanisms such as surface lows, frontal boundaries and upper level troughs configured in a way to produce large amounts of precipitation. In these situations, there can be a swath in which the air aloft is warm enough to melt falling snowflakes into rain droplets that then become supercooled falling through colder air below, finally freezing on contact with surfaces that have a temperature below 32 degrees.
At more northerly latitudes, it is often too cold for snow to melt before reaching the ground, or the overall atmosphere is colder and not as efficient at producing large amonts of precipitation. Even so, there can be serious ice storms in the north, especially over the northeastern U.S. and eastern Canada where some of the warm, moist air associated with the Gulf Stream can be transported in on the north side of strong low pressure systems moving up the eastern Seaboard.
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