A tornado is a violently rotating column of air that extends from a thunderstorm down to the ground. These powerful atmospheric vortices can produce winds exceeding 300 miles per hour, capable of demolishing large buildings, uprooting trees, and hurling vehicles. Recognizing the signs of an approaching tornado is crucial for personal safety and seeking shelter.
Visual Signs in the Sky
One of the most noticeable visual indicators is the formation of a wall cloud, which appears as a lowered, rotating base of a thundercloud. This feature forms beneath the main updraft of a storm and can span from a fraction of a mile to nearly five miles in diameter. Persistent rotation of a wall cloud for five to ten minutes or more suggests an increased likelihood of a tornado developing. Closely related are funnel clouds, which are visible rotating columns of air that descend from the cloud base but do not yet touch the ground. A funnel cloud becomes a tornado only when it makes contact with the surface or stirs up a cloud of dust and debris beneath it.
Even without a distinct funnel, visible rotation within the cloud base or a swirl of dust and debris at the ground can signal an active tornado. Another atmospheric clue is an unusual sky color, often described as an eerie green or a very dark, ominous hue. This coloration can result from sunlight interacting with a high concentration of water droplets and ice particles within a thick thunderstorm cloud, indicating severe weather potential. Additionally, the presence of large hail frequently precedes or accompanies strong thunderstorms capable of producing tornadoes. Both hail and tornadoes are products of the intense updrafts found within severe storm systems.
Sounds That Signal Danger
An approaching tornado often produces a distinctive auditory warning, most commonly described as a continuous roar similar to a freight train. This intense, low-pitched sound results from the immense volume of air, dirt, and debris moving at extremely high speeds within the tornado’s vortex. While the “freight train” comparison is prevalent, others have likened the sound to a jet engine, a powerful waterfall, or a deep rumbling. The specific sound can vary depending on the tornado’s size, strength, and proximity to the observer.
Sometimes, a whistling or hissing sound might be heard as a smaller tornado approaches or is in its formative stages. These acoustic indicators can provide an early alert, particularly during nighttime hours or when visual cues are obscured by heavy rain or terrain. Listening for these specific sounds can offer a vital advantage, allowing individuals to react before the tornado becomes visible.
Subtle Environmental Changes
Beyond visual and auditory cues, less obvious atmospheric shifts can indicate an impending tornado. One such change is a sudden and unsettling calm or stillness in the air, which can occur just before a tornado strikes. This phenomenon happens as the storm’s powerful updraft begins to draw in air from the surrounding environment. This calm can be deceptive, as it often precedes the storm’s most destructive phase.
A noticeable drop in temperature may also accompany a shift in wind direction as the storm system moves through an area. Furthermore, individuals might experience rapid changes in atmospheric pressure, similar to the sensation of ears popping during air travel. This pressure change indicates a significant and rapid decrease in localized atmospheric pressure, a characteristic feature of a tornado’s core. While these subtle signs alone are not conclusive, their presence should heighten awareness, especially when combined with other more direct indicators of severe weather.
Understanding Official Warnings
Official warnings provide authoritative information and guidance, complementing natural observations. A “tornado watch” signifies that conditions are favorable for tornadoes to develop in a designated area. This means that severe thunderstorms capable of producing tornadoes are likely within the watch area, prompting heightened vigilance. In contrast, a “tornado warning” indicates that a tornado has been sighted by trained spotters or detected by weather radar, posing an imminent threat to life and property.
Several reliable sources disseminate these critical alerts. NOAA Weather Radio (NWR) broadcasts continuous weather information, including warnings and watches, 24 hours a day and can activate alarms to alert residents, even during overnight hours. Wireless Emergency Alerts (WEA) deliver emergency messages directly to WEA-capable mobile phones within a threatened area, requiring no prior signup. Local emergency sirens are primarily designed for outdoor notification, and television and radio broadcasts also provide widespread coverage of warnings. Heeding these official warnings immediately is important for safety.