No. 113: Sep-Oct 1997
Anecdotes abound that exceptionally severe thunderstorms may appear to emit an eerie, sickeningly yellow-green light. Skeptics scoff at this notion. The excited observers were deluded, or they made it all up. This is, of course, the same knee-jerk response greeting UFO reports and accounts of many other anomalies. Thunderstorms, however, do have an objective existence. And it turns out that a few storm-watching meteorologists have also seen greenish thunderstorms. Such professional testimony is usually dismissed as due to the reflection of greenish ground vegetation by the storm clouds or, perhaps, the effects of sheets of hail preceding the storms.
In 1995, F.W. Gallagher et al decided to settle the matter. They chased likely looking thunderstorms armed with a spectrophotometer. Many storms later, they proved, first of all, that some thunderstorms are definitely green. In fact, some gradually change from blue to green in the space of half an hour. Their ground observations, plus more spectrophotometer data taken from aircraft, refute the theory that the green color is from reflected vegetation. Hail may contribute to the green color but is not required. In sum, green thunderstorms really do exist, but no one yet knows where all the green comes from.
(Gallagher, Frank W., III, et al; "Green Thunderstorms Observed," Amer ican Meteorological Society, Bulletin, 77:2889, 1996.)