There are about 1,800 thunderstorms in progress around the world at any given time, according to the National Weather Service.
Only a small fraction are classified as severe.
Severe thunderstorms are thunderstorms that produce hail 1 inch in diameter (about the size of a quarter), or larger, and or strong wind gusts of 58 mph or greater.
A small fraction of these thunderstorms produce tornadoes.
All thunderstorms are capable of producing deadly lightning. But the heavy rains or the lightning activity in a thunderstorm do not necessarily mean a thunderstorm is severe.
The National Weather Service's responsibilities include issuing watches, warnings and other information to help keep individuals safe when hazardous weather threatens. They say the best defense against dangerous storms is to have multiple plans of action, depending on the circumstances, and consistently monitor local weather information.
An individual's chances of receiving a severe weather warning depend on where you are, what you're doing and the time of day the warning is issued.
A single warning could turn out to be the most important warning in your life. Knowing how to get information and having multiple ways to hear a warning can help increase the chances you'll hear the warning when it matters most.
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How to develop a plan
Use the guidelines below to develop a personal tornado safety plan for you and your family. Remember you need to have a plan for wherever you may be when a tornado strikes — at home, at school, at work, on the road or in a public building.
Developing a tornado safety kit
These items would be extremely useful to have in your storm shelter, or to take with you to your storm shelter, when severe weather strikes.
• Disaster supply kit: You should store your emergency supplies as close to your shelter as possible.
• Battery-operated weather radio: You will want to be able to monitor the latest information directly from the National Weather Service.
• A map to track storms: You will need to be able to track the progress of the storm. Because warning texts include county names, a county outline map of your area is a great thing to keep handy. You might also keep a state highway map, which includes most of the cities and towns referred to in National Weather Service warnings and statements.
• Shoes: This will be very important if your home is damaged and you must walk across broken glass or other debris.
• Identification: You may need identification to move around in the area should significant damage occur.
• Your car keys.
Other things to consider
• Papers: If you have a safe room or other shelter area, you might consider storing important papers and other irreplaceable items in the shelter if space permits.
• Batteries: Check and replace batteries in your weather radio, flashlights and other devices in your safety kit often, preferably twice a year. Do this at the same time you set clocks back/ahead in the spring and fall.
• Maintain: Check your disaster supplies kit often to maintain fresh food and water.
• Cover: Make sure you have something to cover up with. Pillows, blankets, sleeping bags or a mattress could help to protect you from falling/flying debris.
SOURCE: NATIONAL WEATHER SERVICE