Photos show light pillars in the Pittsburgh-area sky. Here's why the rare phenomenon happens.
PITTSBURGH (KDKA) — Light pillars are becoming visible around the area thanks to the cold temperatures the Pittsburgh area has been experiencing as well as moisture moving in with the next disturbance.
This is a rare phenomenon that is usually reserved for temperatures below zero, but the conditions are right for them to form on Thursday evening. Reports of light pillars have already come in from Jefferson Hills and Apollo.
Light pillars need some very specific ingredients to form. First, you need really cold temperatures. Usually, temperatures fall below zero, but light pillars can occur with temperatures a little warmer than 0 degrees Fahrenheit.
You will also want calm winds and high relative humidity levels. This creates tiny ice crystals that get suspended in the air. These ice crystals are plate- or hexagonal-shaped.
According to NASA, these ice crystals usually evaporate before reaching the ground. During freezing temperatures, however, flat, fluttering ice crystals may form near the ground in the form of light snow, sometimes known as a crystal fog.
The light keeps getting refracted through the ice crystals. And the higher the ice crystals are in the sky, the higher the light pillars can reach upward. Light pillars can come from above, too.
According to the National Weather Service, the light pillars appear as vertical columns of light extending above or below the source of light, which can be streetlights, headlights on cars, or even the moon.
