Many of us have seen the kind of terrifying power a tornado can wield on TV, and a few of us have even lived through one of these twisters. These storms possess an almost god-like presence in the media and our minds. They are dramatic, deafening columns that descend from the sky and obliterate everything in their path. But what are the essentials you need to know about tornadoes?
We still don't know as much about these killer storms as we'd like, but what we've learned in the past 60 years has brought us a lot closer to hopefully, one day, being able to detect them in time to save more lives. This list tries to break down the facts and data we have learned about tornadoes.
Read through the list below to get educated about tornadoes and check out this list of the worst tornadoes in history to see the damage these scary storms can do.
- Photo: Harald Richter (Public Domain Images from National Severe Storm laboratory of NOAA) / Wikimedia Commons / Public Domain
They Form Due To Wind And Altitude
There are a clear set of steps that lead to a tornado:
First, even before the thunderstorm (or supercell) develops, winds will change direction and increase in speed at high altitudes. This creates an invisible, horizontal spinning effect in the lower atmosphere.
Then, rising air inside the thunderstorm’s updraft tilts this newly spinning air from horizontal to vertical.
Next, a two- to six-mile-wide rotation is contained inside the storm. This is where the most violent tornadoes form. After that, the cloud at the central base of the storm begins to take in cool, moist air from the downdraft which converges with the warm air in the updraft, causing a rotating wall cloud. This rapidly descending air is known as the rear flank downdraft (or RFD). This RFD also focuses the developing tornado's base, causing it to siphon air from a smaller and smaller area on the ground. The updraft intensifies and creates an area of low pressure at the surface which pulls the focused mesocyclone down, in the form of a visible funnel.
Finally, as the funnel descends, the RFD also reaches the ground, creating a gust front that can cause severe damage a good distance from the tornado. Usually, the funnel cloud begins causing damage on the ground within a few minutes of the RFD reaching the ground. At that point it is not a funnel cloud and is officially a tornado.
There Are Different Types Of Tornadoes
Supercell tornadoes are the ones most of us are familiar with. They are more likely to remain in contact with the ground for long periods of time (an hour or more) than other tornadoes, and are more likely to be violent, with winds exceeding 200 mph.
Landspout tornadoes are usually weaker than supercells and are not associated with a wall cloud or mesocyclone. They may be observed beneath cumulonimbus or towering cumulus clouds and are the land equivalent of a waterspout. They often form along the leading edge of rain-cooled downdraft air emanating from a thunderstorm, known as a gust front.
Gustnadoes are weak and usually short-lived. They form along the gust front of a thunderstorm, appearing as a temporary dust whirl or debris cloud. There may be no apparent connection to or circulation in the cloud aloft. These appear similar to dust devils.
A waterspout is a tornado over water. A few form from supercell thunderstorms, but many form from weak thunderstorms or rapidly growing cumulus clouds. They form over warm tropical ocean waters, although their funnels are made of freshwater droplets condensed from water vapor due to condensation, not saltwater. Waterspouts can dissipate upon reaching land.
Dust devils form during dry, hot, clear days on the desert or over dry land. Generally forming in the hot sun during the late morning or early afternoon hours, these mostly harmless whirlwinds are triggered by light desert breezes that create a plume of dust. They are not associated with a thunderstorm and are usually weaker than the weakest tornado. Typically, the life cycle of a dust devil is a few minutes or less.
While not classic tornadoes, firewhirls are formed from the intense heat created by a major wildfire or volcanic eruption. A tornado-like rotating column of smoke and/or fire occurs when the fire updraft concentrates some initial weak eddy in the wind. Winds associated with firewhirls have been estimated at roughly 100 mph. They are sometimes called fire tornadoes or firenadoes.
They Exhibit Some Odd Behaviors
Tornadoes are known for the insane things their wind speeds can do. They can wrap a truck around a tree, drive a feather into a telephone pole, or transport a canceled check 150 miles away. In some cases, tornado-borne detritus scours out the ground! One EF5 tornado in 2011 scoured the ground to a depth of two feet!
Tornadoes appear to skip houses
Tornadoes vary in intensity as they move along the ground, sometimes significantly. If a tornado was causing damage, then weakened to the point where it could cause no damage, followed by a re-intensification, it would appear as if it "skipped" a section of its path. Occasionally with very violent tornadoes, a small suction vortex will completely destroy a structure next to another building which appears almost unscathed. The presence of multiple vortices, highly volatile tornadic satellites which orbit the parent tornado at high speeds, are responsible for causing enormous damage right next to an area that takes none.
Bigger doesn't always mean stronger
Most folks assume that small, skinny tornadoes are weaker than scary, large, wedge-shaped tornadoes. While it is true that there is an observable trend of bigger funnels causing worse damage, it is not known if this is due to an actual tendency of tornado dynamics or an ability for the tornado to affect a larger area. Some small, rope-like tornadoes, traditionally thought of as weak, have been among the strongest in history. Also, tornadoes typically change shape during the course of their lifespan.
Appearing to reach the ground
A tornado doesn't have to look like it's touching the ground to cause damage. It's mistakenly thought that if the funnel of a tornado does not reach the ground, then the tornado cannot cause substantial damage. However, the circular, violent surface winds, not the funnel itself, are what both define the tornado and cause the tornado's damage. The sign of a debris cloud will tell a spotter if the tornado is causing damage, not whether it's touching the ground or not. Plus, some tornadoes can be shrouded in rain and might not even be visible at all.
The tornado's path
In the past, it has been assumed that tornadoes moved almost exclusively in a northeasterly direction. Although the majority of tornadoes move northeast, this is normally due to the motion of the storm, and tornadoes can actually arrive from any direction. Additionally, tornadoes can shift without notice due to storm motion changes or effects on the tornado itself from factors such as its rear flank downdraft. Never assume that you know what direction the storm is going.
- Photo: NOAA Photo Library, NOAA Central Library; OAR/ERL/National Severe Storms Laboratory (NSSL) / Wikimedia Commons / Public Domain
They Can Take On Different Shapes
Most tornadoes take the traditional form of a funnel that descends from a wall cloud. However, a tornado can sometimes be shrouded by its storm, making it essentially invisible to the eye and therefore very dangerous.
Sometimes a relatively weak landspout may only be visible as a swirl of dust. Even if the funnel causing the disturbance does not reach the ground, if the wind speeds reach more than 40 mph, it is considered a tornado.
A wedge can be so wide that it appears to be a block of dark clouds, wider than the distance from the cloud base to the ground.
In the dissipating stage, a funnel can resemble a narrow tube or rope, and will often curl or twist into complex shapes. These tornadoes are said to be "roping out," or becoming a "rope tornado." When they rope out, the length of their funnel increases, which forces the winds within the funnel to weaken due to the conservation of angular momentum.
In the US, tornadoes are generally around 500 feet across on average and travel on the ground for five miles. Weak tornadoes, however, or strong yet dissipating tornadoes, can be very narrow, sometimes only a few feet across. One tornado was reported to have a damage path only seven feet long while on the other side of the spectrum, wedge tornadoes can have a damage path a mile or more wide.
Some tornadoes, like the Tri-State Tornado in 1925, travel long distances. Tornadoes like that one, which can go for more than 100 miles, are usually composed of a family of tornadoes which have formed in quick succession. The lifespan of a tornado depends on the severity of the atmospheric instability.
Depending on the environment they travel through, a tornado can be several colors. Those that form in dry places with little loose soil can be nearly invisible, marked by swirling detritus at the base of the funnel. Condensation funnels that pick up little or no detritus can be gray or white. While traveling over a body of water, tornadoes can turn very white or even blue. Slow-moving funnels, which ingest detritus and dirt, are usually darker. Tornadoes in the Great Plains can turn red because of the reddish tint of the soil, and tornadoes in mountainous areas can travel over snow-covered ground, turning white.
Tornadoes normally rotate cyclonically (counterclockwise in the northern hemisphere and clockwise in the southern). While large storms always rotate cyclonically due to the Coriolis effect, smaller tornadoes are not necessarily ruled by the Coriolis effect. Approximately 1% of tornadoes rotate in an anticyclonic direction in the northern hemisphere and, typically, systems as weak as landspouts and gustnadoes can rotate anticyclonically.
Various types of sounds have been reported from witnesses, generally a whooshing roar. Funnel clouds and small tornadoes are reported as whistling, whining, humming, or as the buzzing of bees or electricity, whereas larger tornadoes are reported as a continuous, deep rumbling, or an irregular sound. Since you can usually only hear a tornado when it is dangerously close, sound is not a reliable warning of a tornado.