Decoding the spin: How to tell the difference between a waterspout and a tornado

A waterspout sweeps across Lake Constance off Friedrichshafen, Germany. 

(Dr. Christoph Sommergruber/picture alliance  / Getty Images)

They both spin from the clouds and swirl on the ground, yet they are called different names: waterspouts and tornadoes. 

Tornadoes are born from supercells containing descending currents of relatively cold, dense air, known as downdrafts. These downdrafts help maintain the rotation while also transferring it downward toward lower altitudes.

LEARN: THIS IS A LIFE CYCLE OF A TORNADO

The rotation can eventually become so intensely concentrated that a narrow column of violently rotating air develops. This is called a funnel cloud. If the funnel cloud stretches far enough down that it reaches the ground, it becomes a tornado.

NOAA image of a tornado

So, what's a "waterspout" then? Simply put, a waterspout is just a tornado that is occurring over water. It becomes reclassified as a tornado if a waterspout comes ashore and begins to track across the land.

But there are two types of waterspouts -- one more dangerous than the other.

"Tornadic" waterspouts form from severe thunderstorms just like their tornado cousins. They can accompany strong winds, locally high seas, frequent lightning, and large hail, and thus can be dangerous to mariners suddenly caught in their path. 

Waterspout swirls in the Gulf of Mexico near a NOAA ship in 2009.

(Melody Ovard / NOAA)

Then there are "fair weather" waterspouts, which form only over open water.

"They develop at the surface of the water and climb skyward associated with warm water temperatures, and high humidity in the lowest several thousand feet of the atmosphere," says Meteorologist Bruce B. Smith with the National Weather Service office in Gaylord, Michigan. "They are usually small, relatively brief, and less dangerous." 

Waterspouts can be seen over any large bodies of water but are somewhat common sightings in Florida from late spring into early autumn. They can also be found quite frequently in the Great Lakes from August through October.

The National Weather Service recommends any boaters who spot a waterspout move at a 90-degree angle away from the waterspout's path.

What about a landspout?

If a waterspout is a tornado over water and a tornado is a tornado over land, then what is a landspout? 

Funnel cloud that became landspouts form in Sully County, South Dakota

(Sully County Emergency Manager/Sheriff's deputy via National Weather Service, Aberdeen, S.D.)

It is a type of tornado but forms in a different way. Classic tornadoes form in supercell thunderstorms that contain their own rotating updraft. 

Landspouts occur when you have colliding winds at the surface that will begin to make their own vortex, and then a developing thunderstorm passes overhead. The updrafts from the passing thunderstorm will pull this rotating vortex skyward and make a tornado-like appearance.

Landspout tornado pictured on May 16, 2017 in Elk City, Oklahoma.

(Jason Weingart / Barcroft Images / Getty Images)

Landspouts tend to be pretty weak compared to traditional tornadoes but can still be strong enough to cause damage and warrant caution.

Not a tornado, but it sure looks like one:

There are three other wind phenomenon that involves swirling columns of air but are not considered tornadoes.

"Gustnadoes" form at the head of a gust front and are just swirls of dust and/or debris from strong winds that race out ahead of a thunderstorm’s intense downdraft. They do not connect to cloud bases and do not have a traditional condensation funnel.

Another tornado look-a-like: Dust Devils

On the other hand, dust devils ironically form in fair weather on sunny and hot days with somewhat calm winds. 

Intense heating along the ground causes a vast difference in temperature within a few hundred feet of the ground, causing the heated air to shoot upward with light surface winds providing some spin. 

Dust devils usually only last a few minutes and have low enough wind speeds to rarely cause damage.

Unless you add fire…

And perhaps the most apocalyptic version of the swirl beside a tornado would be fire whirls — which are essentially dust devils caused by fire. 

The rising air from the wildfire’s intense heat creates a column of flames that rise towards the sky. 

NOAA researchers say the most favorable condition for fire whirlwinds is over a fire near the top of a steep slope with strong winds over the ridge top.