Meteorological phenomena conspire to create a host of wild and wonderful outcomes, from “superbolt” lightning that strikes with the force of a low-yield nuclear bomb to pastel-colored “supernumerary” rainbows that occur under the arch of their primary counterparts when sunlight shines through small, similarly-sized water droplets.
There’s also an oft-repeated adage that warns of worrisome weather to come: When skies turn green, tornadoes soon follow. But is there any truth to this green sky tornado theory, or is this color concern merely circumstantial?
Not Easy Being Green
Given the potential property and personal damage powerful tornadoes can cause, it’s easy to position this color palate presumption as nothing more than superstition — an unrelated occurrence that isn’t tied to weather patterns directly but happens adjacent to their occurrence.
In fact, green skies prior to significant storms are well documented, suggesting some type of causal link between color and the creation of catastrophic conditions. In an effort to understand this atmospheric advance warning, scientists have already eliminated several explanations, including:
- Ground reflection — Some theories held that color reflections from green grass or fields were responsible for the observed emerald effect, but the spectra isn’t consistent, and the phenomenon has been observed even when the primary ground color is red or brown soil.
- Optical obfuscation — Just as rainbows appear to have “ends” that touch the ground, it’s been suggested that the green coloration of clouds is simply an optical illusion. However, meteorological analysis of stormy weather wavelengths has confirmed the presence of green light.
Considering Color Theory: Why Does the Sky Turn Green?
Is it the direct result of tornado formation? The time of day? Or something more exotic?
As it turns out, there’s no single explanation that accounts for every shamrock-colored storm and teal-colored tornado, but several theories may explain common causes:
- Low-angle sunlight — In the same way that low-angle light through water droplets after a rainstorm creates rainbows, it’s possible the reddish-yellow glow produced by the rising or setting sun combined with blue sky above conspires to create a subtle greenish cast, which may be enhanced when severe storms provide a dark cloud backdrop. In this case, storms don’t serve as the catalyst for green light but instead make it easier to observe.
- Water vapor wavelengths — Another theory holds that the blue-tinted water held in large amounts by storm clouds combined with low-angle sunlight creates this green coloration as similarly-sized raindrops scatter sunlight into generally uniform wavelengths.
- In-storm situations — It’s also possible that falling hail or flashing lightning may act as the genesis of these green effects. In the case of falling hail, light reflected through its crystalline structure may produce a green color between storm clouds and the ground, while lightning crashing through a dusty sky may take on a yellow tinge against blue clouds and combine to create green.
So, why does the sky turn green during a storm? There’s no simple answer. At best, it’s complicated — and unpredictable.
Seeking Storm Signs
While the green sky tornado theory is scientifically sound, it’s worth noting that, even in areas where severe storms are persistent and tornadoes are perpetual, this phenomenon remains rare. In most cases, inclement weather doesn’t come with a color-first calling card. This makes it more important for observers to watch for more common signs, such as sudden changes in temperature, pressure or wind speed and the visible formation of large or rotating cloud masses.
Put simply? When it comes to powerful storms and pulverizing tornadoes, green is tangentially tied to meteorological machinations. But even without chartreuse-colored clouds or spring-colored skies, severe weather can occur; as a result, it’s better to bank on current conditions than bet on color concerns.
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