Trees throughout the metropolitan area are aglaze with ice crystals this morning, as a hearty layer of hoarfrost has coated the region.
“It’s so moist out there and it’s just cold enough we’re getting ice crystal formation,” said Andy Kleinsasser, a meteorologist with the National Weather Service. “It seems a few times a winter we get really good hoarfrost.”
It takes a pretty narrow set of conditions for hoarfrost to form, Kleinsasser said: temperatures of 20 to 25 or less, a high relative humidity, a thick fog and no wind. That creates an environment for the moist air to form ice crystals on small elevated surfaces such as branches, blades of grass and telephone wires.
Hoarfrost is often called “furry ice” because of its appearance. It is not frozen dew, however.
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The dense fog and little to no wind are key, Kleinsasser said, because the air has to be moist enough and still enough for the ice crystals to form.
For more information on weather conditions, go to our weather page.