Miles City Montana Hoarfrost 2010

Depending on precisely where you live in or around Miles City, you were treated to beautiful hoarfrost between the 4 th and the 6 th of December 2010.

This photograph, taken the first morning of the Miles City hoarfrost, was snapped about 2 miles south of I-94. These Angus cattle are slowly moving to the feed area, where a rancher is putting out large round bales of hay for his herd. Note that even the small leaves on the brush – as well as the backs of the cattle – have hoarfrost on them.

Hoarfrost is a rare and beautiful meteorological event. There are a couple of different conditions which cause hoarfrost to occur. In fact, there are more specific names for hoarfrost – depending on what weather conditions cause them. The type of hoarfrost we just experienced here in Miles City is called an "air hoar." There are also "surface hoarfrost" and "crevasse hoarfrost." Crevasse hoarfrost can't occur in the Miles City area. General hoarfrost itself also goes by other names: "pruina," "white frost" and "hoar frost."

Air hoarfrost occurs when objects become colder than the air around them. This causes white ice crystals to form on all objects that are exposed to the air. If objects are inside of a closed building, they will not have hoarfrost on them. But if objects are outside or even outside but not completely covered, hoarfrost will form on them. The moisture must be able to get to the objects for the hoarfrost to occur.

The thickness of the hoarfrost depends on the contributing weather factors. Our Miles City hoarfrost was pretty thick – at least out here on Moon Creek Road. This indicates that the factors that caused this Miles City hoarfrost lasted for a pretty long time. It occurred during the night, so I don't know exactly how long the frost was forming, but it was thick and hard – and very tough to clear from the windshield.

Hoarfrost is a beautiful event that creates a bright white landscape. Even the year-around green needles of the pine trees are coated with a thick, white frost. Taking photographs in hoarfrost is tricky. All the bright white causes the camera to use a fast shutter speed – thus making darker objects very hard to see by virtue of them being washed out with white. I took three photographs at different shutter speeds to get the one you see with this article. Unfortunately, this is the only photograph I took of the Miles City hoarfrost.

Hoarfrost doesn't bring with it the problems that an ice storm does. Hoarfrost is light and doesn't weigh down and break power lines, tree limbs, etc. Hoarfrost also doesn't substantially diminish road conditions, like ice storms do. Hoarfrost conditions can severely limit visibility. Early the morning of the 5 th, I could only see about 15' in front of me while the fog/frost hung in the air.

Hoarfrost is not a common occurrence. I don't even know when the last true hoarfrost in Miles City occurred. Maybe a Miles City reader will contact me and tell me when the last hoarfrost occurred.

Here is a short, HD video that we took during the hoarfrost and uploaded to our YouTube channel: Milescitymontana.

Here's hoping that you enjoyed the Miles City hoarfrost of 2010. (I'll be sure to change the name if we happen to have another hoarfrost this year.