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John Wheeler, WDAY, Published December 28 2013

Weather Talk: Cold weather has made for lack of freezing rain

Although our December weather has been terribly cold, there is one typical element of winter weather we have not had to deal with so far: freezing rain. And we can thank the cold weather for its absence.

Freezing rain depends on the vertical temperature structure of the atmosphere. Nearly all the time in winter, precipitation begins in the clouds as snowflakes. And most of the time, these fall to the ground as such. But when there is a layer of air that is above freezing, the flakes can be melted.

When the melting layer is thin and the air below is cold enough, the result at the ground is sleet (ice pellets). But when the melting layer is sufficiently deep and the cold air near the ground is very shallow, the melted drops can remain liquid until freezing on contact with the ground. It is not even necessary for the surface air temperature to be below freezing, provided the ground is frozen.

When the surface air

is well below freezing, ice accumulations are at their most dangerous. Ice storms are worse when accompanied by wind because power lines and tree limbs coated with ice are more likely to break in the wind.