Dear Tom,
Does a green sky mean a tornado is coming, or is this just a myth?
—Peter Magner
Dear Peter,
A green sky (or greenish color in clouds) does not mean a tornado is coming, although is a strong indication of hefty rain. Nor does a green sky necessarily mean hail will come. However, the exact cause of a greenish sky in a thunderstorm is still a subject of debate. Dr. Craig Bohren at Penn State University suggested in 1993 that a t-storm occurring around sunrise or sunset, when the sun’s rays take a longer trip through the atmosphere and appear more orangish, could appear green. In 1996, Drs. Bohren and Frank Gallagher at the University of Oklahoma also found that the absorption of sunlight from a rising or setting sun could lead to a greenish color in the clouds.