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John Wheeler, Published January 20 2013

Weather Talk: Sun dogs signify ice crystals in air, not cold temperatures

Most people believe sun dogs are caused by cold weather because we often see sun dogs when it is cold. Sun dogs are actually caused by a reflection of sunlight through a layer of hexagonally shaped ice crystals in the air.

Blowing snow, which is often a result of an arctic cold front, often will hang in the air for a day or so and will often be the cause of sun dogs. But it is rarely just the cold air that is the cause. In certain situations, when cold air is also humid, it is possible for snowflakes to form in clear air, and these can form sun dogs. But usually in our region, blowing snow is the cause.

However, in summer, it is possible for very thin ice clouds near 30,000 feet to create sun dogs, even when the air near the ground is in the 90s. These sun dogs are not as brilliant as the winter ones because the ice crystals are much farther away.

So the next time you see sun dogs, remember that they do not signify cold weather. Look instead for the evidence of ice crystals in the air.


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