What Makes Hoarfrost?

Weather Whys

The KX Storm Team loves getting in your weather photos. Last week, they noticed many of your photos captured the same cold-weather phenomenon.

We’ve been taught since we were kids that when ice melts, it becomes liquid water and when liquid evaporates, it becomes water vapor. But something you may not see is when that water vapor – water in its gas form – turns right into a solid and forms a structure right in front of your eyes.

That’s what frost is… moisture in the air turning straight into millions of ice crystals and forming on anything below freezing. It’s formed just like dew in the morning but it’s in the frozen form. This photo was taken recently by Brad in Williston.

Here’s what you need to form frost: Moisture in the air, a cold ground and surface temperature at freezing or below. The actual air temperature can be slightly above zero.

But with hoarfrost, there’s a lot more moisture to work with. It forms like normal frost only with all that moisture, tiny little ice crystals accumulate to make larger and more picturesque structures. The interlocking ice crystals happen when the air is supersaturated. A good indication of supersaturated air is foggy conditions.

While it’s beautiful, it can also be a nuisance. Especially when scraping it off of your car makes you late for work or school. Here’s something to keep in mind…when the temperature falls to the mid-20s and below, frost is much harder to remove from your windshield than if it were in the upper 20s to lower 30s. This is because the molecular bond is weaker the warmer the ice is. Of course, with this time of year, any frost that forms can be tough to remove since we’re typically seeing single digits and teens.

Hoarfrost from Barb Peerboom in Goodrich
Hoarfrost from Linda Hager-Whisman in Harvey
Tammy Torno Parisien in Bismarck‎
Barb Peerboom near Goodrich

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