Survival House
Log In   |  Forgot Password?  |  Sign Up
YouTube Facebook twitter blog
Tornado

Tornadoes

Tornadoes | Get a Tornado Kit | Make a Plan | Prepare | Build a Safe Room | During the Storm | After the Storm


tor·na·do

A violent destructive whirling wind accompanied by a funnel-shaped cloud that progresses in a narrow path over the land.

Tornadoes are nature's most violent storms and they can appear suddenly without warning. Tornadoes occur in many parts of the world but they are most prevalent in the United States, east of the Rocky Mountains in the spring and summer months. As many as 800 tornadoes occur each year resulting in deaths and injuries along with countless dollars in property damage. The strongest tornadoes are capable of wind speeds of 250 mph or more.

What causes tornadoes?

Tornado conditions are created when different temperatures and humidity meet and form thunderstorms. These thunderstorms often produce large hail, strong winds and tornadoes. For example, high, dry air coming from the north interacts with a low-moving, moist air from the Gulf. The warm winds try to rise but the cold northern air blocks it, creating a clash. The warm trapped air starts to rotate horizontally between the two air masses. As this is happening, more warm air from the surface continues to try and rise. Finally, the rising warm winds become strong enough to force itself through the colder air layer thus forcing the cold air to sink. The warm winds rotate faster and faster in the column. If an updraft is strong, the column can rise to the heights of 10 miles or more.

In the winter and early spring, tornadoes as most often associated with strong, frontal systems that form in the Central States and move East. In the spring, thunderstorms develop along a "dryline" which separates very warm, moist air to the East from hot, dry air to the West. These thunderstorms often produce tornadoes as they move east in the afternoon hours. In the Texas panhandle, front range of Rocky Mountains and in the Southern High Plains, thunderstorms form as the air near the ground flows "upslope" toward higher terrain. If conditions are favorable, these storms can produce tornadoes. Tornadoes occasionally accompany tropical storms and hurricanes as they move inland. These tornadoes are usually are to the right and ahead of the path of the storm as it comes ashore.

Take our Quiz

Sorry, the torando quiz can not display

Tornado Variations

  • Tornadoes can form during the early stages of rapidly developing thunderstorms. This type of tornado is most common along the front range of the Rocky Mountains, the Plains, and the Western States.

  • Tornadoes can be invisible until dust and debris are picked up or a funnel cloud appears.

  • Occasionally, two or more tornadoes may occur at the same time.

  • Some tornadoes appear as a visible funnel extending only partially to the ground. Look for signs of debris below the visible funnel.

  • Some tornadoes are clearly visible while others are obscured by rain or nearby low-hanging clouds.

Waterspouts

  • Waterspouts are weak tornadoes that form over warm water
  • Waterspouts are most common along the Gulf Coast and southeastern states.
  • Waterspouts occasionally move inland becoming tornadoes causing damage and injuries.

The Fujita Scale

The Fujita Scale is used to rate the intensity of a tornado by examining the damage caused after it has passed over a man-made structure.

  • F0 - Gale tornado
    • 40-72 mph winds
    • Some damage to chimneys; breaks branches off trees; pushes over shallow-rooted trees; damages sign boards.
  • F1 - Moderate tornado
    • 73-112 mph winds
    • Lower limit is the beginning of hurricane wind speed
    • Peels surfaces off roofs
    • Mobile homes pushed off foundations or overturned
    • Moving cars pushed off the roads
    • Attached garages may be destroyed
  • F2 - Significant tornado
    • 113-157 mph winds
    • Considerable damage
    • Roofs torn off frame houses
    • Mobile homes demolished
    • Large trees snapped or uprooted
    • Light object missiles generated
  • F3 - Severe tornado
    • 158-206 mph winds
    • Roof and some walls torn off well constructed houses
    • Trains overturned
    • Most trees in forest uprooted
  • F4 - Devastating tornado
    • 207-260 mph winds
    • Well-constructed houses leveled
    • Structures with weak foundations blown off some distance
    • Cars thrown
  • F5 - Incredible tornado
    • 261-318 mph winds
    • Strong frame houses lifted off foundations and carried considerable distances to disintegrate
    • Car sized missiles fly through the air in excess of 100 miles
    • Steel reinforced concrete structures badly damaged


Remember: The size of a tornado is not necessarily an indication of its intensity! Large tornadoes can be weak, and small tornadoes can be violent. Be prepared to act quickly.

Signs that a Tornado may be approaching

Tornadoes occasionally develop in areas in which a severe thunderstorm watch or warning is in effect. Remain alert to signs of an approaching tornado and seek shelter if threatening conditions exist.

Look for these signs:

  • Dark, often greenish sky
  • Wall cloud
  • Large hail
  • Loud roar that has been described as the sound of a freight train
  • Strong, persistent rotation in the cloud base.
  • Whirling dust or debris on the ground close to cloud base.
  • Hail or heavy rain followed by a dead calm or a fast, intense wind shift.
  • At night, small, bright blue-green to white flashes at ground level near a thunderstorm (this could be power lines snapped by strong wind).

Tornado Myths and Facts

MYTH: Mountains are safe from tornadoes.
FACT: No place is safe from tornadoes. In the late 1980's, a tornado swept through Yellowstone National Park leaving a path of destruction up and down a 10,000 ft. mountain.

MYTH: Windows should be opened before a tornado approaches to equalize pressure and minimize damage.
FACT: This is a waste of time. Immediately go to a safe place.

MYTH: Hiding under a freeway overpass will protect me from a tornado.
FACT: The concrete in the bridge may offer some protection against flying debris, the overpass will also act as a wind tunnel. If you are in the path of an approaching tornado, it is safer to abandon your vehicle and take shelter in a road-side ditch or other low spot.

MYTH: You can always out run a tornado in a vehicle
FACT:Tornadoes can move at up to 70 mph or more and shift directions erratically and without warning. It is unwise to try to out race a tornado. It is better to abandon your vehicle and seek shelter immediately.

MYTH: The low pressure with a tornado causes buildings to "explode" as the tornado passes overhead.
FACT: Violent winds and debris slamming into buildings cause most structural damage.

SOME FACTS

  • Tornadoes occur in many parts of the world, but are found most frequently in the U.S.
  • Tornadoes can produce winds in excess of 250 mph.
  • Tornadoes can be more than a mile wide and stay on the ground for more than 50 miles.
  • The average tornado moves from southwest to northeast, but they have been known to move in any direction.
  • Tornadoes can occur any time of the year.
  • They may strike quickly, with little or no warning.
  • They may appear nearly transparent until dust and debris are picked up or a cloud forms in the funnel.
  • The average forward speed of a tornado is 30 mph, but may vary from stationary to 70 mph.
  • Tornadoes can accompany tropical storms and hurricanes as they move onto land.
  • Waterspouts are tornadoes that form over water.
  • Tornadoes are most frequently reported east of the Rocky Mountains during spring and summer months.
  • Peak tornado season in the southern states is March through May; in the northern states, it is late spring through early summer.
  • Tornadoes are most likely to occur between 3 pm and 9 pm, but can occur at any time.

All rights reserved. Survival House