Comment Re:Green skies up above (Score 2) 34
Of the hundreds of storms we've documented over the years, there doesn't seem to be a strong causal link between green storms and tornadoes, or even hail for that matter. The green color appears to be a byproduct of sunlight having its other colors stripped off on its trip through the atmosphere.
Air scatters the blue end of the spectrum more readily (that scattered light is why the sky appears blue). In the late afternoon and evening, sunlight takes a longer path through the atmosphere and much of the blue in the light is gone by the time it reaches a storm, while most of the green and red light is still present. That light paints the storms a nice golden yellow. The yellow light then encounters copious amounts of water, both liquid and solid ice suspended in the storm's updrafts and downdrafts. Water absorbs the red end of the spectrum more readily, which is why it looks blue underwater. So the red light gets stripped off the yellow light going into the storm, and just a chunk of the color in the middle of the spectrum is left over: green. The green light makes it through cracks and gaps in the storm clouds, which is usually where there is a downdraft and precipitation eroding the clouds.
The color is thus dependent on the time of day, and the amount of water suspended aloft. Tall storms tend to produce more hail than short ones as the updrafts are stronger. And atmospheric instability peaks in the late afternoon, so there is some correlation here to severe weather. The problem, however, is that hail and tornadoes depend on a lot more than time of day and updraft height. Freezing level, lapse rates, wind shear, and a myriad of other things play a big part in hail and tornado production. Of the 100+ tornadoes our team has documented over the years, I'd say most did not occur with a particularly green sky. And we've had many instances of a pronounced green color, without tornadoes or any hail at all, probably due to warm air aloft making the lapse shallow and raising the freezing level. The "green sky = hail/tornado" is mostly folklore with a little kernel of truth underneath it seems. Two unusual things happen in conjunction, and that gets cemented into people's brains, even though the connection between them is weak or indirect.