During winter, when we have these days that send me on a hunt to find the difference between rime ice and hoar frost, digging into the weather conditions allows you to get a close-up look at how they virtually look the same.
After conducting some research, it appears that the primary distinction between the two resides in the origin of the moisture.
According to the National Weather Service, hoar frost typically develops when water vapor in the air comes into contact with solid surfaces that are already freezing below the freezing point.
The frost expands as the ice crystals “nourish” and additional water vapor is solidified, creating ice crystals. The quantity of accessible water vapor determines the magnitude of the frost that develops.
When there is little to no wind, lacy complex crystals form, giving frost hoar a distinctive appearance of feathery or hair-like structures as it grows.
The appearance of sharp, icy needles pointing outward generally resembles frost that is thicker and more resembling ice rime rather than dew. Thus, the process of freezing directly from a liquid state to a solid state, or the direct transformation of water droplets into ice rime, typically occurs when moisture from freezing fog is present.
This brief investigation assisted me in determining that the subject I was capturing with my camera this week was indeed hoar frost.
According to AccuWeather, the frost that resembles an old man’s beard comes from age or getting white or grayish, which means it is derived from the English word “hoary,” a scandalous-sounding term that I also apparently learned.
It does make sense that a lot of the frost-covered foliage, particularly evergreens, appears somewhat “hair-like” when you consider their white, fluffy beards.
My favorite spot in town is near the boat landing at Irving Lake, where the Mississippi flows under railroad tracks and bridges. Along the water, you can see a variety of beautiful trees, cattails, and other foliage, and it always looks extra thick and frosty.
I found this article from AccuWeather interesting as it mentions specifically how there will be more moisture in the air when there is a release of moisture from an unfrozen stream or lake, making the flowing air humid.
According to the article, AccuWeather’s Senior Meteorologist Dave Dombek mentioned that, “In the early morning, after daybreak during spring or when sewage treatment plants release downstream, certain areas may offer the most ideal conditions to observe a beautiful frosty layer called hoarfrost.”
So I suppose that’s another reason why it’s such a scenic spot on chilly mornings.