Quick Answer
The sky can take on various colors when a tornado is imminent, depending on the weather and atmospheric conditions. Some common sky colors that may indicate an approaching tornado include:
– Greenish or yellowish – This may signify hail in the thunderstorm that could spawn a tornado. The green/yellow tint is caused by light refracting through hailstones in the storm clouds.
– Dark green or black – These ominous colors are caused by very dense cloud cover and likely an intense thunderstorm. The darkness results from thick storm clouds blocking sunlight.
– Gray or white – A dark gray or nearly white sky signals very heavy precipitation and possibly hail within a severe thunderstorm. The odd colors are due to dense cloud layers and unusual refraction of light.
– Wall cloud/shelf cloud – A wall cloud or shelf cloud (a wide, wedge-shaped arcus cloud) descending beneath the storm’s base may indicate rotation and tornadogenesis. These clouds have a localized area of lowered bases near the center of a storm.
What Causes the Strange Sky Colors Before a Tornado?
The sky can take on weird, unnatural colors before a tornado due to the unique atmospheric and weather conditions inside severe thunderstorms that spawn tornadoes. Here are some key factors that lead to the unusual sky tints:
– Suspended hail – Hailstones suspended aloft in a storm produce scattered light refraction and reflection, leading to green, yellow, orange, or red-tinted clouds. High hail content signifies a powerful updraft that can cause tornadogenesis.
– Cloud density – Extremely dense, low-level cloud layers give the sky a dark, ominous color. Dense clouds form as warm, moist air rapidly rises in a thunderstorm, foretelling possible tornado formation.
– Cloud composition – Low-level clouds containing dense water droplets or ice crystals from heavy precipitation cause gray or white hues by refracting light in unusual ways. This signals substantial lift and turbulence.
– Light blockage – Dark green or black skies indicate very dense clouds blocking sunlight. This extreme light blockage points to powerful thunderstorms that can spawn tornadoes.
– Dust and debris – Tornadoes suck up debris and dirt that can be lofted high into the parent thunderstorm, contributing to odd greenish or brown coloration.
– Microbursts – Localized downdrafts of rain-cooled air hitting the ground can disturb and compress air layers, leading to strange optical effects near the cloud base.
Reading the Sky Colors to Predict Tornadoes
Learning to properly read the sky for signs of tornado activity takes time and experience. Here are some guidelines on interpreting sky colors to gauge tornado potential:
– Isolated green/brown clouds – These likely signify hail and severe weather, but not necessarily an imminent tornado. Look for rotation in the thunderstorm.
– Sky takes on sickly hue – Yellowish, greenish or brownish tint across the whole sky is a troubling sign, signaling possible tornadic development.
– Dark gray shroud – Very dark storm clouds covering the sky is a warning of heavy precipitation and possible wall clouds or funnel clouds below.
– Black/green clouds lowering – Ominous dark green or black clouds descending from the thunderstorm base indicate tornadogenesis may be underway.
– Color borders or tinted edges – Unique hues hugging cloud borders or storm edges may be caused by debris or structural boundaries signifying tornado risk.
– Wall/shelf cloud forms – The formation of a wall or shelf cloud underneath a thunderstorm is a dangerous sign that a tornado may soon form. The rotating wall cloud is connected to the possible tornadic updraft.
– Sky turns green/white – A green and then white sky color transition is very troubling, marking tornado occurrence as highly likely.
– Color rotation – Circular patterns of odd colors rotating around or under a thunderstorm signifies tornadic rotation and an imminent threat.
– Color persists – If the odd sky tinting persists and does not dissipate, it likely means tornadic activity is ongoing or intensifying.
When to Seek Shelter Based on Sky Color
Using sky colors to inform tornado safety decisions takes focused observation, ideally combined with weather radar monitoring. Here are some key sky color benchmarks that signal when to take cover:
– Isolated green clouds – Monitor conditions but may not need shelter yet.
– Yellow/green/brown sky – Be alert and ready to take shelter soon.
– Dark gray clouds lowering – Move to shelter quickly if thunderstorm appears to be rotating.
– Green/black lowering clouds – Take shelter immediately in a basement or interior room.
– Wall cloud formation – Seek sturdy shelter right away, tornado could form at any moment.
– Green sky turning white – Take immediate shelter, tornado likely imminent based on this classic sky color progression.
– Rotating green/white clouds – Get underground or into a fortified inner room without delay, tornado is likely seconds away.
– Persistent odd colors – Remain sheltered until sky returns to normal hue, indicating tornado threat has passed.
Always stay tuned to weather alerts and warnings from trusted local sources. Never rely just on sky color when making safety decisions in possible tornadic situations. Use sky colors as cues to increase alertness, and be ready to urgently take proper shelter at the first sign of a developing tornado based on official guidance.
Scientific Explanations of Tornado Sky Colors
The unusual, often unsettling sky colors that can precede tornado formation have scientific explanations based on meteorology and atmospheric optics. Here are some of the key scientific insights on this phenomenon:
Greenish or Yellowish Sky
– Caused primarily by light refraction through hailstones suspended aloft in powerful thunderstorm updrafts.
– Hail indicates strong rising air motion and turbulence that can lead to tornadogenesis.
– Green/yellow light scattering requires hail pieces between 5-10 mm wide.
– Deeper green color signifies larger hailstones and more severe weather risk.
Dark Green or Black Sky
– Result of very dense, thick storm cloud layers blocking sunlight and turning the sky a dark, ominous hue.
– Darkness caused by exceptional depth and density of storm clouds in the lower levels of the atmosphere.
– Indicates robust lift, moisture and possible strong rotation in the thunderstorm.
– Sky appears darker closer to the thunderstorm due to the thick, towering cloud mass overhead.
Gray or White Sky
– Heavy precipitation and deep, moisture-laden clouds full of water droplets or ice crystals can create a gray or white cast.
– Cloud layers have high liquid water content, causing muted, washed-out sky coloration.
– The odd color results from complex scattering and absorption of sunlight passing through dense clouds.
– White/gray sky signals turbulent storm with intense rain and hail that may spawn a tornado below.
Wall Cloud
– Rotating wall cloud under thunderstorm base indicates highly organized tornadic circulation.
– Outflow of rain-cooled air from storm creates distinctive lowering of cloud base at center.
– Marks boundary between updraft and downdraft regions in a supercell thunderstorm.
– Persistent, smooth wall cloud is a prime precursor of imminent tornadogenesis.
Conclusion
When an ominous, sickly green sky turns black or white before a thunderstorm, it often portends tornadic development. While sky colors alone should not dictate safety actions, recognizing these tornado precursor colors can help spur proper preparedness and protective decisions when combined with weather alerts. Since minutes matter in tornado events, observing the sky and interpreting these warning colors while seeking sturdy shelter can save lives. Through understanding the meteorology behind the eerie sky tints, we can better anticipate severe weather changes and react prudently based on patterns learned through science and experience.
