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It seems to be a fairly widely held belief that if the sky is green or yellow, a tornado may be developing/approaching. But is there any truth to it? Could the color of the sky actually be associated with the hail that usually accompanies a tornado?

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    $\begingroup$ Apparently not. $\endgroup$ – naught101 Apr 16 '14 at 11:14
  • $\begingroup$ It can vary. The belief is held due to the fact that a green cast to the sky indicates heavy hail/rain and the yellow is often due to dust in the air. So, no, not necessarily a sign of a tornado but certainly can be! $\endgroup$ – L.B. Sep 11 '15 at 14:08
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You know, there hasn't been too much research into this... but there has been some. For the most part, it's been proven that a green sky most likely means that a thunderstorm is coming. According to a researcher:

Green is significant, but not proof that a tornado is on the way. A green cloud “will only occur if the cloud is very deep, which generally only occurs in thunderstorm clouds,” Bachmeier says. “Those are the kind of storms that may produce hail and tornadoes.” Green does indicate that the cloud is extremely tall, and since thunderclouds are the tallest clouds, green is a warning sign that large hail or a tornado may be present.

In addition, a Scientific American article was run on this:

Over the past 15 years, a small group of scientists have weathered the elements working on green thunderstorms as a pet project, publishing a handful of articles in meteorological journals. All point to the existence of green skies with severe thunderstorms but no direct connection to tornadoes or hail can be made.

They then go on to state:

Threatening green skies during a thunderstorm also proved entirely independent of the type of severe weather that came with it. Gallagher measured hailstorms where the dominant wavelength of light was green as well as hailstorms where it was the typical gray-blue color of thunderstorms. Tornado-producing storms proved similarly divorced from any particular sky color, other than dark.

We do know that green skies are a sign of thunderstorms, though:

The moisture particles are so small that they can bend the light and alter its appearance to the observer. These water droplets absorb red light, making the scattered light appear blue. If this blue scattered light is set against an environment heavy in red light—during sunset for instance—and a dark gray thunderstorm cloud, the net effect can make the sky appear faintly green.

So to sum all of this up: we know that thunderstorms sometimes create a green sky. However, there is no evidence to prove that a green sky is a sure sign of a tornado or hail. It is however a warning sign, as it shows that a thunderstorm is most likely coming, and it could be a strong storm.

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    $\begingroup$ Doesn't your whole answer say the exact opposite of "it shows that a thunderstorm is most likely coming"? It'd be more correct if you replaced "most" with "more", perhaps, but it still sounds like it might be overstating it (none of the quotes mention any actual probabilities though, so I'm not sure). $\endgroup$ – naught101 Sep 8 '14 at 2:46
  • $\begingroup$ Naught101 he did say in the answer, that Green skies do mean a thunderstorm is coming and it could be strong… he said that it does not 100 percent mean a tornado is. That has not been scientifically proven so there is no definite answer. So him saying "it shows that a thunderstorm is most likely coming" is true. $\endgroup$ – user3286 Aug 4 '15 at 11:28

protected by Community Aug 9 '17 at 16:40

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