Back Roads: Hoarfrost: Nature’s Lace

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The mountains encased in hoarfrost. Photo: Lynn Coffey.

Waking up in the morning and looking out to see the mountaintops covered in beautiful snow-white lace always makes me think someone has sifted powdered sugar over the ridges while I was sleeping.  

Looking closer, the “lace” appears to be made up of thin, needle-like appendages called hoarfrost.

I always assumed that hoarfrost was the same thing as light snow, frost, or rime ice, but it has different properties that set it apart as well as differing weather conditions that produce it.

Snow is made up of individual ice crystals that grow while suspended in the atmosphere, usually in the clouds, and fall to the ground.

Frost is a thin layer of ice on a solid surface, which forms from water vapor in a freezing atmosphere coming in contact with a solid surface whose temperature is below 32 degrees. This results in the water vapor (gas) turning to ice (solid) as the water vapor reaches the freezing point.

View of hoarfrost “lace” from our backporch. Photo: Lynn Coffey.

Rime ice forms white incrustations of ice when super-cooled water droplets in fog freeze and fall to the ground like light fluffy snowflakes. This ice grows into combs and needles of feathery designs.

Hoarfrost can best be described as “frost on steroids!” The term comes from Old English, meaning frost resembling an old man’s white feathery beard.

“Hoarfrost” forms on cold, humid nights with clear skies. From a more scientific viewpoint, it forms when moisture in the air skips the water droplet stage and appears directly as stunning ice crystals on objects such as trees, plants, and wire fencing.  It is much more rare and photogenic than regular run-of-the-mill windshield frost.  The “needles” of ice in hoarfrost can be several inches long in some cases and can form on the sides and beneath objects as well as on top.  These needles will grow in the direction from which the moisture is arriving. The air must be quite moist for hoarfrost to form, while regular frost may form when the air is dry.

Hoarfrost “needles” on wild rose bush. Photo: Lynn Coffey.

If the weather conditions are just right, you may witness the beauty of hoarfrost for yourself this winter. Take a moment for a closer look and perhaps take a few photographs of the intricate patterns on ordinary objects that have suddenly become extraordinary, thanks to Mother Nature! 

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