About a year ago I wrote a column about two types of frost. On the chance you missed that column, or are new to the area, we had a great example of both types on the frigid morning of January 5th, 2016. (Presque Isle was 20 below that morning).
Many trees that morning were an icy white against a cobalt blue sky. They had been covered in frost. But actually two totally different things were happening to create two totally different types of frost!
Down by the river, with the water still open, areas of dense fog formed, and it formed not as an ice fog, where you can actually see the ice needles suspended in the air, but instead as super-cooled water droplets. Water can exist at temperatures well below freezing, and when it hits something, like a tree or a pole, it will immediately freeze. This forms a white coating of ice, of a rather uniform thickness, unless the wind is blowing in which case it can extend outward, downwind, from that to which it is attached.
This type of ice is known as Rime Ice, and it famously has to be attacked by the weather observers on the summit of Mt. Washington on a regular basis, lest it freeze their instruments. They sometimes have to chisel away at this thick rime ice build-up in winds over 100 mph!
By the way, if you did not know, Mt. Washington had a measured-by-humans wind gust of 231 mph in April of 1934 and I urge readers to visit this link to the story of the observers on shift that day! Go to: https://www.mountwashington.org/about-us/history/world-record-wind.aspx You’ll be amazed !
But I digress. I started this column talking about the two types of frost we had on that recent bitter morning. Well the other type is called Hoar Frost (the word “Hoar” derives from Middle English). With Hoar Frost, the ice skips the water droplet phase and goes directly from water vapor to ice crystals in a process called deposition (not the legal kind!).
This is the type of frost that forms intricate, delicate ice crystals on every limb and twig. If you blow on it, it comes right off. If you look closely at it, it almost looks like tiny stalagmites.
The best thing for you to do is to Google on each term, “Rime Ice” and “Hoar Frost”, to see the amazing images of each online. And again, on the morning of January 5th, we had both, right here in The County!
Ted Shapiro holds the Broadcast Seal of Approval from both the American Meteorological Society and the National Weather Association. An Alexandria, Va. native, he has been chief meteorologist at WAGM-TV since 2006. Email him at tshapiro@wagmtv.com.
