Tornadoes

What is a tornado?

A tornado is a violently rotating column of air extending from a thunderstorm to the ground.

A thunderstorm is, in general, a local storm, invariably produced by a cumulonimbus cloud and always accompanied by lightning and thunder, usually with strong gusts of wind, heavy rain, and sometimes with hail.The typical thunderstorm is 15 miles in diameter lasts an average of 30 minutes. Of the estimated 100,000 thunderstorms that occur each year in the United States, about 10 percent are classifiedas severe.

Is a tornado a cyclone?

Yes, a tornado is a cyclone. But a hurricane is a cyclone too. A cyclone is a general term referring to an area of closed circulation. While a tornado is a type of cyclone, so too is a hurricane, and even the big "L" you see on a weather map. The "L" on the weather map stands for low pressure, but it is on a synoptic scale (a large scale measuring hundreds of miles or more), while a tornado is on a micro-scale or storm-scale.

Tornadoes are found most frequently in the US

In an average year, 1,200 tornadoes cause 70 fatalities and 1,500 injuries nationwide.

"Tornado Alley," or the states at the highest risk of getting a tornado, include Arkansas, Iowa, Kansas, Louisiana, Minnesota, Nebraska, North Dakota, Ohio, Oklahoma, South Dakota, and Texas.

Most tornadoes form from thunderstorms. You need warm, moist air from the Gulf of Mexico and cool, dry air from Canada. When these two air masses meet, they create instability in the atmosphere.

North America is a relatively large continent that extends from the tropical south into arctic areas, and has no major east-west mountain range to block air flow between these two areas. This unique topography allows for many collisons of warm and cold air; creating the conditions necessary to breed strong, long-lived storms which occur many times a year.

How does a tornado form?

Tornado Alley

How does a tornado form?

Under tornado-favorable condition, a wind shear (a change in wind direction and an increase in wind speed with increasing height) creates an invisible, horizontal spinning effect in the lower atmosphere.

Step 1: Spinning in the lower atmosphere

Rising air within the updraft tilts the rotating air from horizontal to vertical.

How does a tornado form?

Step 2: Lifted and tilted from horizontal to vertical

An area of rotation, 2-6 miles wide, now extends through much of the storm. Most strong and violent tornadoes form within this area of strong rotation.

How does a tornado form?

Step 3: Extending and Forming

Weak Tornadoes

88% of all tornadoesLess than 5% of tornado deathsLifetime 1 - 10+ minutesWinds less than 110 mph

Tornadoes Take Many Shapes and Sizes

Strong Tornadoes

11% of all tornadoesNearly 30% of all tornado deathsMay last 20 minutes or longerWinds 110-205 mph

Violent Tornadoes

Less than 1% of all tornadoes70% of all tornado deathsLifetime can exceed 1 hourWinds greater than 205 mph

Fujita Scale of Tornado Intensity

SCALE WIND SPEED POSSIBLE DAMAGE

F0 40-72 mph Light damage: Branches broken off trees; minor roof damage

F1 73-112 mph Moderate damage: Trees snapped; mobile home pushed off foundations;roofs damaged

F2 113-157 mph Considerable damage: Mobile homes demolished; trees uprooted; strong built homes unroofed

F3 158-206 mph Severe damage: Trains overturned; cars lifted off the ground; strong built homes have outside walls blown away

F4 207-260 mph Devastating damage: Houses leveled leaving piles of debris; cars thrown 300 yards or more in the air

F5 261-318 mph Incredible damage: Strongly built homes completely blown away; automobile-sized missiles generated

Where and when tornadoes occur?

Tornadoes can occur at any time of the year and any time of the day.

Tornadoes have occurred in every state, butthey are most frequent east of the RockyMountains during the spring and summermonths.

In the southern states, peak tornado occurrenceis March through May, while peak months inthe northern states are during the late springand summer.

Tornadoes are most likely to occur between3 and 9 p.m. but can happen at any time.

Deport, Texas

Hoxie, Kansas

Northeast, Nebraska

Tornado in Salt Lake City

On August 11, 1999, an F2 tornado touched down in the metropolitan area of Salt Lake City. The tornado lasted ten minutes and killed one person, injured more than 80 people, and caused more than $170 million in damages. It was the most destructive tornado in Utah's history.

Salt Lake City Tornado, Aug. 11, 1999

Orange fireball is a power sub-station exploding.

Total Tornadoes: 124

Number of Tornadoesby Month January 1February 1March 4April 7May 29June 18July 15August 24September 21October 0November 2December 2.

Tornado Statistics for Utah January 1950 to

PresentNumber of Injuries:

2 people on July 8, 19891 male on August 14, 19681 female on April 19, 19701 male on April 23, 19902 people on June 2, 19931 female on May 29, 19965 people (or more) on August 20, 199880 people (or more) on August 11, 19991 female on September 3, 1999

Number of Deaths:

1 male on August 11, 1999(Note: 1 young female was killed on July 6, 1884.)

A waterspout is just a weak tornado that forms over water. They are most common along the Gulf Coast. Waterspouts can sometimes move inland, becoming tornadoes causing damage and injuries.

What is a waterspout?

What is a gustnado?

A gustnado is a short-lived, relatively weak whirlwind that forms along a gust front. A gust front is the surge of very gusty winds at the leading edge of a thunderstorm's outflow of air. Gustnadoes are not tornadoes. They do not connect with any cloud-base rotation. But because gustnadoes often have a spinning dust cloud at ground level, they are sometimes wrongly reported as tornadoes. Gustnadoes can do minor damage.

A gustnado in southeastern Wisconsin on 4 October 2002.

Storm relative motion images from the Evansville Doppler Radar (VWX) at 1:58 a.m., which was near the time the tornado ripped through the Eastbrook Mobile Home Park. Note the strong rotational couplet.

Weather Radar Watches the Sky

Damage by the CRITTENDEN-WEBSTER COUNTY KENTUCKY F-3

TORNADO, November 6 2005

Red: Tornado WarningPurple: Flash Flood WarningTo see if there are any active warnings in your

area, go to: http://www.weather.gov/view/largemap.php

TORNADO WATCH - Tornadoes are possible in your area. Stay tuned to the radio or television news.

TORNADO WARNING - A tornado is either on the ground or has been detected by Doppler radar. Seek shelter immediately!

Tornado watch and warning

Tornado Facts

1. Tornadoes may appear nearly transparent until dust and debris are picked up or a cloud forms within the funnel.

2. The average tornado moves from southwest to northeast, but tornadoes have been known to move in any direction.

3. The average forward speed is 30 mph but may vary from nearly stationary to 70 mph.

4. The strongest tornadoes have rotating winds of more than 250 mph.

5. Tornadoes can accompany tropical storms and hurricanes as they move onto land.

Tornado Safety Tips

BEFORE A TORNADO: Have a disaster plan. Make sure everyone knows where to go in case a tornado threatens. Make sure you know which county or parish you live in. Prepare a disaster supplies kit for your home and car. Include a first aid kit, canned food and a can opener, bottled water, battery-operated radio, flashlight, protective clothing and written instructions on how to turn off electricity, gas, and water. DURING A TORNADO: Go to a basement. If you do not have a basement, go to an interior room without windows on the lowest floor such as a bathroom or closet. If you can, get under a sturdy piece of furniture, like a table. If you live in a mobile home get out. They offer little protection against tornadoes. Get out of automobiles. Do not try to outrun a tornado in your car, leave it immediately. If you’re outside, go to a ditch or low lying area and lie flat in it. Stay away from fallen power lines and stay out of damaged areas.IF YOU’RE AT SCHOOL DURING A TORNADO: Every school should have a disaster plan and have frequent drills. Basements offer the best protection. Schools without basements should use interior rooms and hallways on the lowest floor away from windows. Crouch down on your knees and protect your head with your arms.AFTER A TORNADO: Stay indoors until it is safe to come out. Check for injured or trapped people, without putting yourself in danger. Watch out for downed power lines. Use a flashlight to inspect your home.

Tornado Videos