Weather for Kids

Tornadoes are one of natures' most dangerous and destructive weather events associated with thunderstorms. A tornado is defined as a violently rotating column of air extending from a thunderstorm to the ground. Tornadoes are very rare west of the Rocky Mountains but more common in the Midwest, which is sometimes referred to as "tornado alley." Scientists still debate why tornadoes develop, however meteorologists have a good understanding of the ingredients needed to generate one.

Before a thunderstorm develops, a change in wind direction and an increase in wind speed above the ground creates an invisible, horizontal spinning in the atmosphere. When a thunderstorm grows, strong updrafts within the storm tilt the rotating air from horizontal to vertical. This rotating updraft is the part of a thunderstorm most favorable for tornadoes to form.

Tornadoes can occur at any time of the year and anywhere in the country, even in Alaska. Nearly 90% of all tornadoes are classified as weak tornadoes, lasting less than 10 minutes with wind speeds less than 110 mph. Only 1% of tornadoes are violent, but they can have a lifetime over one hour and have wind speeds greater than 200 mph. Tornadoes may appear nearly transparent until dust and debris are picked up from the ground. And, it's possible to have two or more tornadoes occurring at the same time.

Weak tornadoes that form over water are called waterspouts. Waterspouts start out nearly invisible and usually develop as a ring of rotating spray on the surface of a lake or ocean. As water is pulled up the funnel to the base of the thunderstorm, the waterspout becomes visible. Waterspouts have occurred on Flathead Lake in northwest Montana in the past and sometimes cause damage when they move onshore.

The effects of tornadoes give us many incredible stories. Have you ever heard the saying "it's raining cats and dogs"? Well tornadoes have been known to pick up frogs and fish from lakes, depositing them miles from their watery home. Tornadoes have lifted freight train cars from their tracks, made pretzels out of automobiles, and carried debris like tree branches and signs well over 30 miles away.