Why Green Sky Isn’t Always A Sign Of A Tornado
InstantWeatherEvery summer we are reminded of how quickly severe weather can develop on a hot, humid day where all conditions are just right. Reports start to flow in with announcements of severe weather heading your way coupled with watches and warnings. You’ve been studying the sky for hours, but on this particular day something looks different; the sky turns an eerie green. Do you head to the basement? Not necessarily, some scientists claim.
Have you ever wondered what that eerie green sky really means? Is there a tornado coming? Is there a bad hail storm heading your way? Theories have been thrown around for many decades as to what causes the green colour and how this colour can determine the severity of a storm. Only recently scientists have discovered green storm clouds along with dark stormy clouds are similar in that they are only a precursor to severe weather and not necessarily tornadoes or hail. However, more recent research has now focused on studying the theory of the formation of green thunderstorms.
Often green sky is associated with severe weather, however scientists have taken the time to examine this theory in more detail. What has been a side project for a group of scientists in tornado alley for the past 15 years has lead to some interesting findings as to whether the green hue of a severe thunderstorm actually meant impending tornadoes and hail. Is the green sky simply an optical illusion where the light was being reflected from the ground back up into the storm?
Meteorologist Frank Gallagher, a graduate from the University of Oklahoma, recently had his work published in the Journal of Applied Meteorology regarding this concept. His studies lead him to travel alongside the storm chasing team VORTEX, through several states in tornado alley focusing his graduate work on this theory.
His findings showed that although the wavelength of light was green in several severe thunderstorms, the color was independent of the ground beneath the storm. This meaning, an open green pasture was not a contributing factor to creating the illusion of green skies during severe weather. Green wavelengths did not make a difference in what ground conditions were at the time of the storm and did not reflect back into the clouds. In fact, many of the storms were over dry, drought-like conditions so that theory was debunked.
His studies also determined no correlation of the severity of the storm comparing the darkened green skies to a general darkened, severe, high precipitation thunderstorm. His work included studying the wavelengths in a hail storm with a green sky in contrast to a hail storm with the typical grey-blue hue. There was no link determining the colour difference in the sky to the severity of the hail storm itself.
Many researchers are still puzzled by the cause of green skies during severe weather but many agree it likely has something to do with the liquid water content in the air. The theory is that if the water particles are very small, it allows them to bend light and alter the view to anyone on the ground who is looking at the cloud. More research needs to be done in the area of “green thunderstorms”, but all experts agree it has something to do with the way certain spectrums of light play on the storm clouds and the time of day at which the storm is present.
Although green skies usually means severe weather is likely on the way, it has been identified regardless of the colour of the supercell storm clouds, a green-hued storm doesn’t pack any more of a punch than a darkened blue-grey coloured supercell storm.
-IW (Suzanne P.)
https://weather.com/science/weather-explainers/news/green-sky-thunderstorm-hail
https://www.theguardian.com/news/2013/sep/29/weatherwatch-green-clouds-tornadoes-hail
http://earthsky.org/earth/why-does-the-sky-change-color-before-a-tornado
https://www.accuweather.com/en/weather-blogs/weathermatrix/debunked-the-gr/9597