National Geographic Website Notes



National Geographic Website Notes

Tornadoes

A tornado is a violently rotating column of air that extends from a thunderstorm to the ground. Tornadoes are some of the Earth’s most violent events.

Most tornadoes occur in the United States. Some have been reported in Great Britain, India, Argentina, and a few other countries, but most tornadoes occur in the United States. Most tornadoes in the United States occur in Tornado Alley. Tornado Alley stretches from Texas to Nebraska and also includes Colorado, Iowa, Indiana, Illinois, Kansas, Missouri, and Arkansas. Texas holds the record for the most tornadoes.

Waterspouts are weak twisters that form over warm water. They sometimes move inland and become tornadoes.

Dust devils are small, rapidly rotating columns of air that are made visible by the dust and dirt they pick up. Dust devils are not associated with thunderstorms.

The most violent tornadoes come from supercells, large thunderstorms that have winds already in rotations.

Tornado season begins in early spring for the states along the Gulf of Mexico. The season follows the jet stream. May generally has more tornadoes than any other month, but April’s twisters are usually more violent. Tornadoes can occur at any time of the day or night, but most tornadoes form in the late afternoon. By this time the sun has heated the ground and the atmosphere enough to produce thunderstorms.

Tornadoes form when warm, humid air collides with cold, dry air. The denser cold air is pushed over the warm air, usually producing thunderstorms. The warm air rises through the colder air, causing an updraft. This updraft will begin to rotate if winds vary sharply in speed or direction. The updraft is called a mesocyclone. The mesocyclone draws in more warm air from the moving thunderstorm. Its rotation speed increases. Cool air fed by the jet stream, a strong band of wind in the atmosphere provides even more energy. Water droplets from the mesocyclone’s moist air form a funnel cloud. The funnel continues to grow and eventually it descends from the cloud. When it touches the ground, it becomes a tornado.

Twisters are usually accompanied or preceded by severe thunderstorms and high winds. Hail is also common. Winds can reach up to 300 miles per hour.

The Fujita scale measures a tornado’s intensity by analyzing the damage the tornado has done and then matching that to the wind speeds estimated to produce comparable damage. The scale ranges from F0 to F5.

Meteorologists at the U.S. National Weather Service us Doppler radar, satellites, weather balloons, and computer modeling to watch the skies for severe storms and tornadic activity. Doppler radars record wind speeds and identify areas of rotation within thunderstorms. Since Doppler radar has been in use, the warning time for tornadoes has grown from fewer than five minutes in the l980’s to an average of 13 minutes today.

The National Weather Service issues a tornado watch when weather conditions are conducive for tornado formation. A tornado warning is issued when a tornado has been sighted or indicated on radar.

Conditions must be right for tornadoes to form.

Atmospheric conditions for a twister:

Cold, dry air mass Falling Pressure

Warm, moist air mass Variable Winds

National Geographic Website Notes

Tornadoes

A ______________is a violently rotating column of air that extends from a ____________________to the ground. Tornadoes are some of the Earth’s ___________________events.

Most ________________occur in the___________________. Some have been reported in Great Britain, India, Argentina, and a few other countries, but most tornadoes occur in the United States. Most tornadoes in the United States occur in_________________. ________________________stretches from Texas to Nebraska and also includes Colorado, Iowa, Indiana, Illinois, Kansas, Missouri, and Arkansas. ________________ holds the record for the most tornadoes.

________________________are weak twisters that form over warm water. They sometimes move inland and become tornadoes.

_______________are small, rapidly ____________columns of air that are made visible by the dust and dirt they pick up. _____________________are not associated with thunderstorms.

The most violent tornadoes come from______________, large thunderstorms that have winds already in rotations.

Tornado season begins in early spring for the states along the Gulf of Mexico. The season follows the_____________________. ________________generally has more tornadoes than any other month, but April’s twisters are usually more_____________. _______________________can occur at any time of the day or night, but most tornadoes form in the late_________________. By this time the __________has heated the ground and the atmosphere enough to produce thunderstorms.

_________________form when warm, humid air collides with cold, dry air. The denser ____________________is pushed over the__________________, usually producing thunderstorms. The warm air rises through the colder air, causing an____________. This updraft will begin to rotate if winds very sharply in speed or direction. The updraft is called a________________________. The mesocyclone draws in more warm air from the moving thunderstorm. Its rotation ____________increases. Cool air fed by the jet stream, a strong band of wind in the atmosphere provides even more_________________. Water droplets from the mesocyclone’s moist air form a__________________. The funnel continues to grow and eventually it descends from the cloud. When it touches the ground, it becomes a_________________.

_____________________are usually accompanied or preceded by severe ______________________and high winds. ____________is also common. _____________can reach up to 300 miles per hour.

The ____________scale measures a tornado’s intensity by analyzing the damage the tornado has done and then matching that to the wind speeds estimated to produce comparable damage. The scale ranges from_____________________.

__________________________at the U.S. National Weather Service us Doppler radar, satellites, weather balloons, and computer modeling to watch the skies for severe storms and tornadic activity. _____________________record wind speeds and identifies areas of rotation within thunderstorms. Since Doppler radar has been in use, the ______________________for tornadoes has grown from fewer than five minutes in the l980’s to an average of _______ minutes today.

The ___________________________issues a tornado _____________when weather conditions are conducive for tornado formation. A tornado __________________is issued when a tornado has been sighted or indicated on radar.

Conditions must be right for tornadoes to form.

Atmospheric conditions for a twister:

Cold, dry air mass Falling _____________

Warm, moist air mass ___________________

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