Back in January after a dip below freezing, we found loads of hair ice in a nearby nature preserve. Having found hair ice elsewhere before, I have gained a sense for when and where it might appear. Good conditions for hair ice, at least here in the Seattle area: mornings when the ground can freeze, a wet area with hardwood logs, a region with significant sky view such as a clearing. In this case, we saw the first bits on the edge of a clearing and then much more in a boggy area that was almost entirely hardwoods (and thus in winter clear of overhead foliage). Overhead foliage affects the ground temperature.
What’s the deal with the influence of foliage and having a sky view? Though you might not notice the change in temperature, it is slightly warmer when there are more woody things above you, such as when you are under a conifer. Woody things, indeed pretty much everything except shiny metal and some gases, emit infrared radiation that provide some warming to objects in their “view”. This is why cloudy nights are generally warmer: the clouds send down more infrared than does the clear sky. And this is why you generally do not see any, or at least relatively little, morning dew or hoarfrost near tall objects or under bushes. Of course, the air temperature also matters. If it gets very cold, then even places deep in a forest and with little sky view can have hair frost. After all, the key ingredients for hair ice are temperature, wetness, and suitable woody material that can produce hair ice. But for regions like Seattle, it rarely gets very cold so the clearer areas are more likely to have hair ice.
Needle and other ground ice can indicate a possible day to find hair ice.
I learned about hair ice nearly 20 years ago, and for years I would look for it without success. Such excitement I had when I spotted my first bit of hair ice about 13 years ago. Once I saw it that time, I’ve seen it nearly every winter because I know where and when to look in these parts. I wonder how many other people at that nature preserve noticed it? To me, you could not miss it because it seemed to be everywhere. Yet of the dozens of folks walking past us as we crouched down with our cameras, none asked what we were looking at.
The hair ice may completely overwhelm the underlying wood.
Hair ice does not grow through bark, though it may grow underneath it and push it outward.
This endpiece’s hair ice resembles Santa Claus.
There is much more to say about hair ice, but that’s it for now.
— Jon