1/11/21 – Minnesotans have been waking up to spectacularly frosted landscapes as of recent, including us. Up until now I would have described this phenomenon as hoarfrost, but meteorologists have been characterizing it as “rime ice,” adding a new term to my vocabulary and prompting some research into the difference between the two.
Most of what the state has been experiencing lately is called rime ice, which is caused when liquid water, in the form of clouds or low fog, comes in contact with something solid (such as trees), which it then freezes onto. Rime ice is generally on the heavier side and can look like frozen droplets.
Hoarfrost, on the other hand, is formed under clear, cold skies. The moisture in the air goes from a gaseous state straight to its solid form, skipping the liquid (i.e. clouds or fog) in between. Generally this type of frost is light and feathery and can be easily blown from whatever it clings to.
In the words of the great Bill Nye, “Did you know that…Now you know.” -Jessica
Source: CBC News article “Here’s why you need to know the difference between hoarfrost and rime ice” from February 11, 2020.