Green Color in Thunderstorms

March 17, 2012

GreenstormDSCF0615-Crop1

Photographer: Claude Oesterreicher
Summary Author: Claude Oesterreicher; Jim Foster

Featured above is a photo of a storm cloud that roared through north central Illinois on July 11, 2008. It was taken from my front porch as it moved from northeast to southwest (from right to left in the photo). This is opposite to the direction thunderstorms typically move in the mid-latitudes of the Northern Hemisphere. Note the green fringe along the leading edge of this storm -- visible here for only 45-60 seconds. Green in storms has long been associated with severe weather, particularly hail. However, this is the case only on occasion, and the presence of hail isn't sufficient to account for a storm's greenish color. Neither hail nor funnel clouds were reported during this storm. Green coloration in storms seems to be related to reddish sunlight (corresponding to the time of the day the storm occurs or the position of the Sun in the sky) and the absorptive properties of water within the storm (corresponding to the liquid content of the storm clouds). The light illuminating the clouds, the color of the background against which they're observed, their thickness, and perhaps raindrop size likely have roles to play as well.