If a tornado "watch" is issued for your area, it means that a tornado is "possible."
If a tornado "warning" is issued, it means that a tornado has actually been spotted, or is strongly indicated on radar, and it is time to go to a safe shelter immediately.
Be alert to what is happening outside as well. Here are some ways that describe the tornado experience:
- A sickly greenish or greenish black color to the sky.
- If there is a watch or warning posted, then the presents of hail should be considered as a real danger sign. Hail can be common in some areas, however, and usually has no tornadic activity along with it.
- A strange quiet that occurs within or shortly after the thunderstorm.
Clouds moving by very fast, especially in a rotating pattern or converging toward one area of the sky.
- A sound like a waterfall or rushing air at first, but turning into a roar as it comes closer. The sound of a tornado has been likened to that of both railroad trains and jets.
- Debris dropping from the sky.
- An obvious "funnel-shaped" cloud that is rotating, or debris such as branches or leaves being pulled upwards, even if no funnel cloud is visible.
- Hail almost always precedes a tornado.
|TORNADO SAFETY TIPS|
Go to storm shelter or basement.
Go to rooms nearest center of house.
|IN HIGH-RISE OR OTHER PUBLIC BUILDINGS:
(Schools, Hospital, Nursing Homes, etc.):
Move to interior (preferably a stairwell or hallway.)
|IN YOUR CAR:
STOP!! Get out and lie flat in a low area. Cover your head.
|IN OPEN COUNTRY:
Lie face down in a low area (ditch or ravine, if nearby). Cover your head
Stay in mobile home. Seek Shelter elsewhere.
Try to outrun the tornado on foot or in your car.
Open the windows.
The Red Cross suggests that you assemble a "disaster supplies kit" that you keep in your shelter area. It should contain:
- A first aid kit with essential medication in addition to the usual items.
- A battery powered radio, flashlight, and extra batteries.
- Canned and other non-perishable food and a hand operated can opener.
- Bottled water. (3 gallons per person, do not forget pets)
- Candles and matches.
- Sturdy shoes and work gloves.
- Written instructions on how to turn off your home utilities.
STAGES OF A TORNADO'S LIFE There are four main stages in a tornado's life. These are the organization stage, the mature stage, the shrinking stage, and the decaying stage. In the organization stage, a funnel appears and touches down. The tornado is at its largest in the mature stage. The funnel then decreases to a thin column in the shrinking stage, and becomes fragmented and very disorganized in the decaying stage, although it is still a destructive funnel. Tornadoes require an almost perfect atmosphere to form. Warm moist air must collide with cooler, drier air to form massive storms known as super cells. Despite all the necessities needed, tornadoes form in great numbers across a stretch of the United States know as Tornado Alley. In this area, warm, moist Gulf air meets with cool, dry Canadian air during the spring and early summer months. This results in a large number of storms during this part of the year.
When the warm air meets the cooler air, the warm air rises, and then condenses to form clouds. When an area of warm air rises very quickly, it is known as an updraft. Updrafts cause the cloud tops to grow higher and higher, sometimes as high as ten miles. High winds in the upper atmosphere sometimes cause the tops of the storm to be blown to the northeast. This is known as the anvil of the storm. The clouds underneath this anvil are generally free of rain. The rain falls to the northeast of the anvil.
Super cells form along an area of instability known as a squall line. A squall line is an area of cooler air out in front of a cold front. This cooler air meets with the warmer air first, sometimes forming very destructive storms. A super cell is a very characteristic storm. It is named "super" because of its extreme organization. Whereas most storms have several updrafts and downdrafts that interfere with each other, a super cell has one updraft and downdraft. This allows the storm to feed off itself, giving it a long and intense life. These storms often produce very gusty winds, heavy rain, large hail, and even tornadoes.
Wind shear, which is winds blowing from different directions at different altitudes and speeds, causes the air around it to begin rotating horizontally. When this horizontal column of air meets one of the strong updrafts, it can become twisted and bent upward. This mass of rotating air is known as the meso-cyclone. The tornado will usually form within this area of rotating air. The funnel usually appears at the southwest edge of the storm and southwest of an updraft, close to its adjacent downdraft. A wall cloud or a lowering of the cloud base in a specific area is usually seen before tornado development.
This sequence of shots shows the formation of a tornado. You can clearly see the organization stage in the first two pictures, the mature stage as debris is sucked up, causing the funnel to turn black, the shrinking stage as the tornado thins out, and finally the decaying stage when the
The tornado funnel is said to contain several smaller funnels known as "suction vortices." A single tornado may have as many as six, or as few as one suction vortices. The width of these vortices depends on the width of the funnel, but may range from .5 to 50 meters in diameter. They may be stationary or rotate around the center of the funnel, and they contain the strongest winds of the tornado. A complex pattern of narrow trails of debris is often left behind a tornado with multiple suction vortices, and these tornadoes are among the most destructive. Suction vortices have been know to contain vortices themselves (as seen by Professor Fujita). This can be described by the famous rhyme of L. F. Richardson:
Big whirls have little whirls that feed upon their velocity
And little whirls have lesser whirls and so on to viscosity.
This EF-scale is used by surveying the degree of damage that a tornado has caused. This method works well for estimating the intensity of a tornado, however, since damage is required for an estimate, tornadoes, which occur in the open country, are hard to categorize.
* An F6 tornado has never been observed. This is a theoretical value, which lists the strongest storm estimated to be possible.
- EF-0: 65 to 85 mph - Light damage. Peels surface off some roofs; some damage to gutters or siding; branches broken off trees; shallow-rooted trees pushed over
- EF-1: 86 to 110 mph - Moderate damage. Roofs severely stripped; mobile homes overturned or badly damaged; loss of exterior doors; windows and other glass broken
- EF-2: 111 to 135 mph - Considerable damage. Roofs torn off well-constructed houses; foundations of frame homes shifted; mobile homes completely destroyed; large trees snapped or uprooted; light-object missiles generated; cars lifted off ground
- EF-3: 136 to 165 mph - Severe damage. Entire stories of well-constructed houses destroyed; severe damage to large buildings such as shopping malls; trains overturned; trees debarked; heavy cars lifted off the ground and thrown; structures with weak foundations blown away some distance
- EF-4: 166 to 200 mph - Devastating damage. Whole frame houses Well-constructed houses and whole frame houses completely leveled; cars thrown and small missiles generated
- EF-5: Over 200 mph - Incredible damage. Strong frame houses leveled off foundations and swept away; automobile-sized missiles fly through the air in excess of 100 meter high-rise buildings have significant structural deformation; incredible phenomena will occur
IF YOU HAVE ANY QUESTIONS, CALL YOUR LOCAL EMERGENCY MANAGEMENT OFFICE.
IF YOU SEE A TORNADO REPORT IT TO YOUR LOCAL 911 CENTER IMMEDIATELY.