Skies turn green from a severe line of storms

A derecho leaves damage in South Dakota and many people puzzled

The right thickness of clouds can reflect green light under just the right conditions, such as when the sun is at a low angle or clouds have the right diameter of water droplets.

Skies turned an ominous green in Sioux Falls, South Dakota, Tuesday before a massive squall line called a derecho swept through the state with near 100 mph winds.

The green cast was witnessed by many people and left them wondering what was happening in the sky.

The derecho is a fast moving well organized line of storms than can sustain itself for several hours. It results in destruction similar to that of a tornado but winds blow in one direction along a relatively straight path that extends at least 240 miles.

The scale of these massive systems extends over 60 miles wide and they can appear much darker than most storms by effectively blocking out sunlight.

Sometimes green skies can develop before or during thunderstorms becoming harbingers for hail.

In this squall line over South Dakota, the skies turned green before the rain, likely due to sunlight passing through clouds preceding the rain shaft.

The moisture-laden water droplets suspended in the sky scattered the sunlight in a manner that lent a green hue to the overcast.

This rare optical event needs a unique set of sun positioning and storm features, and it all came together for the cameras.


About the Author:

After covering the weather from every corner of Florida and doing marine research in the Gulf, Mark Collins settled in Jacksonville to forecast weather for The First Coast.