Tornados

Where Do They Come From?

Tornados come from the energy released in a thunderstorm. As powerful as they are, tornados account for only a tiny fraction of the energy in a thunderstorm. What makes them dangerous is that their energy is concentrated in a small area, perhaps only a hundred yards across. Not all tornados are the same, of course, and science does not yet completely understand how part of a thunderstorm's energy sometimes gets focused into something as small as a tornado.

How Do Tornados Form?

	Before thunderstorms develop, a change in wind direction and an increase in wind speed with increasing height creates an invisible, horizontal spinning effect in the lower atmosphere.
	Rising air within the thunderstorm updraft tilts the rotating air from horizontal to vertical.
	An area of rotation, 2-6 miles wide, now extends through much of the storm. Most strong and violent tornados form within this area of strong rotation.
	A lower cloud base in the center of the photograph identifies an area of rotation known as a rotating wall cloud. This area is often nearly rain-free. Note rain in the background.
	Moments later a strong tornado develops in this area. Softball-size hail and damaging "straight-line" winds also occurred with this storm.

 Where Do They Occur?

Whenever and wherever conditions are right, tornados are possible, but they are most common in the central plains of North America, east of the Rocky Mountains and west of the Appalachian Mountains. They occur mostly during the spring and summer; the tornado season comes early in the south and later in the north because spring comes later in the year as one moves northward. They usually occur during the late afternoon and early evening. However, they have been known to occur in every state in the United States, on any day of the year, and at any hour. They also occur in many other parts of the world, including Australia, Europe, Africa, Asia, and South America.

Carolinas Outbreak	Pennsylvania-Ohio Outbreak	Plains Outbreak
-- March 28, 1984 -- afternoon-evening -- 22 tornados -- 57 deaths -- 1,248 injuries -- damage $200 million -- 37% of fatalities in mobile homes	-- May 31, 1985, -- late afternoon-evening -- 41 tornados, including 27 in PA and OH -- 75 deaths in U.S. -- 1,025 injuries -- damage $450 million	-- April 26-27, 1991, -- afternoon of 26th  through early morning 27th -- 54 tornados -- 21 deaths -- 308 injuries -- damage $277+ million -- 15 deaths in/near mobile homes, 2 deaths in vehicles

Meteorologists rely on weather radar to provide information on developing storms. The National Weather Service is strategically locating Doppler Radar across the country which can detect air movement toward or away from the radar. Early detection of increasing rotation aloft within a thunderstorm can allow life-saving warnings to be issued before the tornado forms.  

Can they be predicted?

Yes, but only to a limited extent. Although the process by which tornados form is not completely understood, scientific research has revealed that tornados usually form under certain types of atmospheric conditions. Those conditions can be predicted, but not perfectly. When forecasters see those conditions, they can predict that tornados are likely to occur. However, it is not yet possible to predict in advance exactly when and where they will develop, how strong they will be, or precisely what path they will follow. There are some "surprises" every year, when tornados form in situations that do not look like the right conditions in advance, but these are becoming less frequent. Once a tornado is formed and has been detected, warnings can be issued based on the path of the storm producing the tornado, but even these cannot be perfectly precise about who will or will not be struck.  

How can I keep myself safe?

A complete list of tornado safety rules can be found at the FEMA Tornado Safety WebSite (also see FEMA for Kids).To summarize briefly, the main point is to be protected from flying and falling debris. A storm shelter is your best choice, if you have one. If you have a basement, go there and get under something sturdy to shelter you from falling debris (for instance, a strong workbench, or a staircase).

If you have no basement or storm shelter, go to an interior room without windows on the first floor of your home. Bathrooms are a good choice because the plumbing reinforces the walls. Closets are also a good choice since they normally have no windows. The idea is to put as many walls between you and an approaching tornado as possible; flying debris can penetrate exterior walls.

Stay away from windows entirely! It used to be thought that opening windows would reduce a tornado's damage to a home. This is no longer considered to be good advice: leave windows alone completely and get to a safe place immediately.

If you live in a mobile home, it should be abandoned; seek shelter in a neighboring frame home or, better yet, a storm shelter. If you are in a motor vehicle in an populated area, do not try to drive away from a tornado; abandon your vehicle and seek shelter nearby.

If you are traveling in a rural area, drive away from the tornado at a right angle to its path. If caught in the open, get down in a sheltered low spot, and cover your head with your arms; hang on to something if it is available.

If you are at school or work, your school or workplace should have an approved tornado safety plan, which you should follow. If no such plan exists, complain to someone that a plan needs to be developed!! Knowing what to do in a specific situation means you are less likely to panic and do something dangerous without realizing it. Have a plan within your family about what you would do, and follow it exactly, including where you will go if you are separated.

If you hear a tornado warning, you should seek immediate shelter and not waste precious seconds to see if it is true for you; wasting a few minutes in a safe place once in awhile is better than becoming another tornado statistic!  

What is the smallest, largest, average size?

The answer to this depends on what is being measured ... the easiest way to answer this is by the size of the damage path. Also, it is important to note that the "average" can be misleading, since most tornados are small ... a simple average puts too much emphasis on the infrequent large events. A way around this is to use what is called the "median" to represent what is typical. The typical tornado damage path is about one or two miles, with a width of about 50 yards. The largest tornado path widths can exceed one mile, and the smallest widths can be less than 10 yards. Widths can vary considerably during a single tornado, because the size of the tornado can change considerably during its lifetime. Path lengths can vary from what is basically a single point to more than 100 miles. Note that tornado intensity (the peak windspeeds) is not necessarily related to the tornado size ... bigger is not necessarily stronger!

Tornados Take Many Shapes and Sizes

Weak tornados 69% of all tornados  Less than 5% of tornado deaths  Lifetime 1-10+ minutes  Winds less than 110 mph

Strong tornados 29% of all tornados  Nearly 30% of all tornado deaths  May last 20 minutes or longer  Winds 110-205 mph

Violent tornados Only 2% of all tornados  70% of all tornado deaths  Lifetime can exceed 1 hour  Winds greater than 205 mph

How long is a tornado usually on the ground?

Detailed statistics about the time a tornado is on the ground are not available. This time can range from an instant to several hours ... what is typical is roughly 5 minutes or so.  

How fast do tornados move?

As with tornado duration, detailed statistics about forward speed are not available. Movement can range from virtually stationary to more than 60 miles per hour ... what is typical is roughly 10-20 miles per hour.  

How do I know if it is a tornado or just a funnel?

The definition of a tornado means that the vortex of rapidly rotating air must be in contact with the ground. This means that to be a tornado, the swirling winds must be at the surface, capable of doing damage. If you see debris (dust and other objects swirling in the winds), it is definitely a tornado, even if there is no visible funnel cloud. If you can't see debris with a funnel cloud, then it might be a tornado but you can not be certain that it is (or is not). A tornado can move over a surface with few objects to be picked up and swirled about, or you may not be able to see all the way to the surface beneath a funnel cloud because of intervening hills, trees, or buildings. All funnel clouds should be treated as if they are tornados, unless you can be certain that they will not touch down...and being certain about such things is difficult. Even if the funnel is not in contact with the surface when you first see it, that situation can change quite rapidly!  

How do I stay informed?  

  

By listening to NOAA Weather Radio, commercial radio, and television for the latest tornado WATCHES and WARNINGS.

When conditions are favorable for severe weather to develop, a severe thunderstorm or tornado WATCH is issued.

Weather Service personnel use information from weather radar, spotters, and other sources to issue severe thunderstorm and tornado WARNINGS for areas where severe weather is imminent.

Severe thunderstorm warnings are passed to local radio and television stations and are broadcast over local NOAA Weather Radio stations serving the warned areas. These warnings are also relayed to local emergency management and public safety officials who can activate local warning systems to alert communities.

The National Weather Service continuously broadcasts updated weather warnings and forecasts that can be received by NOAA Weather Radios sold in many stores. The average range is 40 miles, depending on topography. Your National Weather Service recommends purchasing a radio that has both a battery backup and a tone-alert feature which automatically alerts you when a watch or warning is issued.

What To Listen For...

TORNADO WATCH: tornados are possible in your area. Remain alert for approaching storms.
TORNADO WARNING: A tornado has been sighted or indicated by weather radar. If a tornado warning is issued for your area and the sky becomes threatening, move to your pre-designated place of safety.
SEVERE THUNDERSTORM WATCH: Severe thunderstorms are possible in your area.
SEVERE THUNDERSTORM WARNING: Severe thunderstorms are occurring.

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