Waterspout

Episode #7 of the course “Rare and Unusual Weather Phenomena”

A waterspout is a column of water that collects a large, low-hanging mass of clouds to the still water over which it is forming. Usually they are observed in coastal areas, although waterspouts can occur over large lakes. They also usually occur in subtropical or tropical zones, but they have been reported in cooler waters throughout the world, too.

There are two types of water spouts—one is relatively slow and harmless (“fair weather waterspout”), and one resembles a giant tornado and can do great damage (“tornadic waterspout.”) Waterspouts can happen at any time of year, and more than one can occur at one time in an area. In some areas of the world such as the Florida Keys, as many as 400 waterspouts per year are recorded. Nine simultaneous waterspouts were once reported over Lake Michigan.

Because waterspouts depend on the tension of wind that brings the water in the air together with the water on the ground, they do not generally move over great distances. Fair weather waterspouts are far more common because they are not associated with thunderstorms. They form from the water surface to the air, have internally mild winds of about 65 miles per hour, and tend to dissipate after 20 minutes or so.

Tornadic waterspouts, however, occur during thunderstorms and form from the movement in the clouds. They are essentially tornadoes over water, and if they come on land, a tornado warning is generally issued. In very rare cases, a tornadic “snowspout” can form over snow on the ground when snow storm weather meets conditions that would normally produce fog. A snowspout is so rare, however, that only six pictures of one are currently available.

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