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363

tornadoes

OLogy Series
geology
card
363

tornadoes

OLogy Series
geology

Tornadoes are nature's most powerful storms. These swirling funnels of wind can rip cars, trees, and even houses from the ground. Tornadoes get their start from thunderstorms, when fast winds high in the atmosphere set a storm cloud spinning. As a tornado forms, the sky fills with low, dark clouds. As it approaches, there may be a loud "roar" like an oncoming train. People in some parts of the U.S. know these warning signs all too well.

How a Tornado Forms

What sets a tornado into action?

It all begins with a large thunderstorm. Thunderstorms form when warm, wet air rises and mixes with cool, dry air above. When the warm air rises, the water vapor cools and condenses, forming large storm clouds of water droplets and ice.

Sometimes winds at higher altitudes blow faster and in a different direction than those below, a situation called wind shear. Wind shear makes the storm cloud tilt and rotate.

During a strong storm, more warm air gets swept up into the storm cloud. This updraft can make the storm cloud spin faster. At the same time, falling cool air produces a small cloud called a wall cloud.

Inside the wall cloud, a funnel cloud forms and extends towards the ground. It causes air on the ground to rotate, and begin to rip up the earth. When the funnel cloud meets the churning air near the ground, it becomes a tornado.

When the updrafts lose energy, the tornado does too, and it slowly disappears.

Most tornadoes take place in "Tornado Alley," an area in Central U.S. There, _____ air from the Arctic mixes with _____ air from the Gulf of Mexico.

cool, dry; warm, humid

cool, humid; warm, dry

cool, dry; cool, humid

Are you right?

Correct!

Thunderstorms often form where cool, dry air mixes with warm, humid air. In Tornado Alley, these conditions are also mixed with warm, dry air from the southwest.

Meteorologists use radar to track severe storms like tornadoes. Radar works by:

detecting light waves from storm clouds

bouncing radio waves off the rain, hail, or snow in a storm

measuring infrared waves from the Sun that pass through storm clouds

Are you right?

Correct!

The amount of time it takes for the radio waves to return tells scientists how far away the storm is. Radar provides up-to-the-minute information about the storm's path. If radar detects that precipitation is blowing in a circular pattern, that's a sign that a tornado might be forming.

The safest place to be during a tornado is a storm shelter or basement. If you can't do that, move to:

the innermost room of a building

the highest level of a building

any corner of the building

Are you right?

Correct!

The safest place to be is on the lowest level of a building, in an inside room like a hallway or closest. Stay away from windows and outside walls. If you're outside and can't get indoors, lie down in a low, flat area. Remember to protect your head.

Although scientists have captured many images of tornadoes, we have no images from inside a tornado.

Fact
or
Fiction
?

Fiction

Tornado scientists place probes in a tornado's path. These probes have cameras or instruments to record wind speed and direction, air pressure, humidity, and temperature.

A tornado "watch" means there are thunderstorm conditions that could start a tornado, but a twister has not been spotted.

Fact
or
Fiction
?

Fact

When a twister has been spotted, meteorologists issue a tornado "warning." This system is designed to give people in the storm's path time to get to safety.

A disaster supply kit should include one small water bottle for each person in your family.

Fact
or
Fiction
?

Fiction

A disaster supply kit should include enough water for three days-that's three gallons of water per person! A kit should also have food, medicine, blankets, and flashlights.

Definition: a strong rotating funnel of air stretching from a thunderstorm cloud to the ground
Frequency: about 1,300 strike the U.S. every year
Wind Speeds: the most powerful ones can reach over 300 miles (480 km) per hour!
Measurement: the Enhanced Fujita (EF) Scale describes a tornado's wind speeds based on the damage it causes (ratings EF0-EF5)
Largest on Record: nearly 2.5 miles wide, near Hallam, Nebraska on May 22, 2004
Cool Fact: The 200-plus-mph winds can bend metal!

Image credits: © AMNH.