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Serving Northern St. Louis County, Minnesota

Hoarfrost brightens many a winter morning

Keith Vandervort
Posted 12/29/20

REGIONAL - Hoarfrost can create dramatic and stunning scenes as ice needles form on objects in the wintertime, but what exactly is it and how does it form?The term “hoarfrost” is derived …

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Hoarfrost brightens many a winter morning

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REGIONAL - Hoarfrost can create dramatic and stunning scenes as ice needles form on objects in the wintertime, but what exactly is it and how does it form?
The term “hoarfrost” is derived from the Old English, meaning frost resembling an old man’s beard.
From a more scientific standpoint, frost or hoarfrost forms when moisture in the air skips the water droplet stage and appears directly as ice crystals on an object.
However, hoarfrost is much more rare and photogenic than standard ice formations. For one, the needles of ice in hoarfrost can form on the sides of and beneath objects, as well as on top, and in extreme cases become several inches long. Frost and hoarfrost can only form when the air and objects are at or below freezing.
While frost may form when the air is relatively dry, for hoarfrost to form there must be an influx of moisture into the region while the air remains sufficiently cold, according to AccuWeather meteorologist Dan Kottlowski. That moisture can be in the form of more humid air gently flowing into the area or the release of moisture from an unfrozen stream or lake.
“The moisture released by a warm stream is deposited in the form of long ice needles on below-freezing objects,” said Kottlowski.
“Sometimes the frost needles will grow into the direction from which the moisture is arriving, such as one side of a metal fence or tree versus the other,” said AccuWeather meteorologist Bob Smerbeck.

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