You don’t see this every day on Sand Mountain! Sure, we get halos, sundogs, and arcs in the sky on a weekly basis, but we rarely see them at ground level here in Alabama. This 22º halo from Peggy Ponds in Albertville on Tuesday, December 11th is quite a find.
Why so rare?
Halos, sundogs, and arcs form when sunlight is refracted through ice crystals. Those crystals are hexagonal plates that look something like this:
As the sunlight bends into the spectrum upon exit from the plate, it shows off the optical phenomenon we see as a ring around the Sun or Moon.
On Tuesday, we had freezing fog that was precipitating out small ice crystals that were shaped like this. The closest description I can find to what we observed is from the Arctic and Antarctic: diamond dust.
We were in no wise ‘Arctic’ Tuesday morning, but conditions were just right for something like that diamond dust to develop in North Alabama. Here’s a video I shot from Research Park in Huntsville showing the small crystals ‘snowing’ down out of a clear sky:
One thing’s for sure: the weather is never really boring. There’s always something cool to find if you’re looking in the right place!