There was a little more freezing fog around the Upper Midwest overnight, which provided another chance to consider the advantage of living in flyover country. Light pillars, for example.
Wisconsin seems to be ground zero for the airborne display.
— Tom Purdy (@TomPurdyWI) December 10, 2018
What caused the beauty? Pollution. Dirt. Ugliness.
Over to you, Washington Post Capital Weather Gang:
Returning to the sounding, we notice that the temperature increases with height in this narrow layer hanging just above the ground. That’s unusual in the atmosphere. It’s called an inversion. Inversions trap pollutants at the surface, preventing them from rising.
It is likely that particulates from vehicles and other fine elements from the ground got penned up within the surface layer on a hyperlocal level. It’s possible that there was just enough nucleation for sufficient crystallization to create the pillars, while still leaving some supercooled droplets to trigger the freezing fog.
Above the inversion, the air dries out and warms up. That may explain why the top of Purdy’s light pillars appear to fan out and become more diffuse. It’s probably the changing air above the thin surface layer. The pillars Purdy captured are short, compared with past examples. According to atoptics.co.uk, “the higher the crystals in the atmosphere, the taller the pillar.”
Related: Winter Magic: The beauty of freezing fog, rime ice, and hoar frost (Updraft)