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Hoarfrost: Frost on Steroids

Jon Erdman | TWC
Published: January 29, 2013

Goldendale, Wash.

Goldendale, Wash.

iWitness Weather

Six days of sub-freezing temperature at Puget Sound Energy's power plant in Goldendale, Wash. left a growing hoarfrost on anything exposed to the wind, including these headlights. (Photo credit: iWitnessWeather user gardnertoo)

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Unless you've spent your life in Hawaii, you've likely seen frost covering grass, car tops, and maybe adding a few minutes to your morning commute.

But have you seen frost like the photos above?  Is this frost on performance-enhancing drugs?  

What you're seeing is a phenomenon called "hoarfrost".  Let's dive into the "Met 101" explanation below.

Science Behind "Hoarfrost"

First, to produce frost, you need water vapor (gaseous form of water) in the air over cold ground with a surface dew point at least as cold as 32 degrees.

When water vapor molecules contact a cold surface, such as a blade of grass, they jump directly from the gas state to solid state (known as "deposition"), leading to a coating of tiny ice crystals.

What conditions produce the incredible scenes depicted in the photos above?

Generally speaking, you want a much more moist air mass in place.  In the winter, one or more days in a row of freezing fog (fog with surface temperatures of 32 degrees or colder) is a perfect scenario.  

With more moisture in the air, the interlocking crystal patterns of frost become more intricate and much larger, known as hoarfrost.  

Perhaps the single best example I've seen of hoarfrost occurred in January 2013 in Washington state.

IWitnessWeather contributor gardnertoo sent us incredible photos, some of which are in the slideshow above.  According to our contributor, six day's worth of sub-freezing temperatures, along with a light breeze, produced the impressive hoarfrost.

If there is a light wind, the hoarfrost tends to orient itself on the downwind side of objects.

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People walk in the snow-covered Champs-Elysees in Paris after the snow fell over the French capital this week. (Mehdi Fedouach/AFP/Getty Images)

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