Recognizing and labelling mid-winter weather phenomena is something like an art form among Maine’s meteorologists. They have identified Arctic sea smoke, thunder snow, Alberta clippers, and a host of other artfully named conditions and events. But so far, I’ve never heard them mention what I call “winter tree feathers.”
Of course, it’s not unusual for ordinary Mainers’ observations of rare weather phenomena to be left out of a professional meteorologist’s lexicon. But after some research, I found that there might be a scientific — if only partial — explanation for what I witnessed some years back. And I suspect winter tree feathers are uniquely Maine marvels. Here’s how I described them in a letter to a friend in Florida several winters ago:
“The other day, the thermometer decided to hop on its toboggan for the overnight, bottoming out around minus 5 just before sunrise. That in itself wasn’t especially notable. But as the temperatures dropped and we slept, an eye-catching phenomenon took hold.
“A form of fog known as Arctic sea smoke drifted in from the nearby estuarial waters of the Sasanoa and Kennebec rivers. It wasn’t like summer fog or any other fog that I know of, including ordinary sea smoke. Rather, there seemed to be some sort of a weird temperature inversion that kept this fog from settling on the ground. In the pre-dawn hours, it just drifted ever so slightly among the treetops around the house.
“As the sky slowly brightened in the southeast, I could see legions of fat flakes had precipitated out of this fog and stuck to the topmost branches of our 90-foot pines, 70-foot oaks, and a few lesser maples and birches. The lower branches, however, were untouched. The result was that the top 10 feet or so of all the trees around the house had a muted-white, feathery appearance. Giant white flakes hung together, each one daintily attached to the other, creating long, lovely tendrils of ice.
“When the sun neared the horizon and the fog retreated, those white feathers turned pinkish, as did the eastern sky. Then the pink began to glitter. As the sun rose higher, the pink slowly transformed back to a sparkling, dazzling white that contrasted with the deep-blue, cloudless sky. The fog had vanished with the first hints of sun, backing off to the open waters of the Sasanoa and Kennebec.
“But the show continued when the sun struck those millions of delicate feathers hanging from the forest canopy. Within minutes, they started to fall, one by one at first, then in a virtual squall of snowflakes, glinting and winking rainbows in the brilliant rising sun. Before the sun was even 2 degrees above the horizon, my ‘feathers’ were on the ground. I had just enough time to wake my wife to see it all.
“She said she felt as if we were living in one of those fairytale snow globes you sometimes see in tourist shops. Too bad we couldn’t shake it up again. I never thought that, after getting this far in life, I’d see a winter weather wonder that I’d never seen before.”
My snowbird friend wrote back and speculated that I’d probably seen some form of hoarfrost. Unfortunately, the meteorology texts I’ve consulted since have proved inconclusive. For hoarfrost to form, you only need a little excess water vapor in the air over cold ground, generally 32 degrees or slightly less. When plants such as flowers, trees, or bushes cool to well below freezing on a cold, clear night — during which any ambient heat radiates up into the sky — that’s when hoarfrost materializes on their surfaces. The more moisture there is in the air, the more complex and intricate the interlocking patterns of ice crystals become.
But hoarfrost seems to be confined primarily to ground-level objects. The wise old weather texts seem to say nothing about similar ice formations high in trees.
I’ve also considered a phenomenon that hardcore winter-weather fans (of which Maine has more than its share) refer to as “diamond dust.” It too appears during clear, frigid nights or even on below-zero, sunlit days. It may resemble a light, fog-like cloud or tiny ice crystals tumbling out of the empty blue. These crystals can even accumulate on ground surfaces but, like hoarfrost, I found no examples of them dangling like feathers from treetops.
In the end, I gave up pondering my tree feathers like I was some sort of armchair scientist. Sometimes the poetry of a Maine winter is best left for the one or two brief readings you get in a lifetime. I’m content to live inside a snow globe that cannot be shaken at will.