I got an email from a friend in Australia this morning describing a problem with weather at the New Mexico site where his robotic telescope is housed. Along with record cold temperatures, he said locals described "snow coming out of a cloudless sky". Living and observing from the frozen tundra of Michigan, I knew instantly what he was referring to. It's called frozen fog. The last time I'd seen it was in 2004. At the time, I wrote about it to the AAVSO Discussion List.
Just after midnight this morning I had to close the dome, in spite of the
fact there wasn't a cloud in the sky and virtually no wind. The culprit:
When the humidity approaches 100% and the temperature and conditions are
just right, the sky begins to snow without the presence of clouds. It always
catches me by surprise because I just don't expect snow when there isn't a
cloud in the sky! It's a pain for astronomy, but it is every bit as
beautiful as the northern lights.
Frozen fog doesn't fall really, it just appears and then gently settles on
things. You can literally watch it form before your eyes. Like magic, it
just comes out of nowhere. It has a very sticky nature, so it tends to stick
to everything it touches; trees, bushes, houses, hats, gloves...
Watching it precipitate under the icy blue glow of a full moon was quite a
treat. I held my hand up in front of the moon and watched frozen fog turn my
glove into a pure white, flaky decoration bathed in moonlight that looked
good enough to eat.
When the sun comes up the landscape has been transformed into a wintry
paradise, sprinkled with pure white, glistening fairy dust. Most people get
up and assume it snowed last night, but I know better. It's magic...frozen