Marine Corps Air Station Iwakuni, Japan


What is a thunderstorm?

A thunderstorm is formed from a combination of moisture, rapidly rising warm air and a force capable of lifting air such as a warm and cold front, a sea breeze or a mountain. All thunderstorms contain lightning. Thunderstorms may occur singly, in clusters or in lines. Thus, it is possible for several thunderstorms to affect one location in the course of a few hours. Some of the most severe weather occurs when a single thunderstorm affects one location for an extended time.

Some thunderstorms can be seen approaching, while others hit without warning. It is important to learn and recognize the danger signs and to plan ahead. Learn the thunderstorm danger signs. Dark, towering, or threatening clouds. Distant lightning and thunder. Because light travels much faster than sound, lightning flashes can be seen long before the resulting thunder is heard. Estimate the number of miles you are from a thunderstorm by counting the number of seconds between a flash of lightning and the next clap of thunder. Divide this number by five. You are in danger from lightning if you can hear thunder. Knowing how far away a storm is does not mean that you are in danger only when the storm is overhead.

A severe thunderstorm watch is issued when the weather conditions are such that a severe thunderstorm (damaging winds 58 miles per hour or more, or hail three-fourths of an inch in diameter or greater) is likely to develop. This is the time to locate a safe place in the home and tell family members to watch the sky and listen to the radio or watch TV channel 6 for more information and wait for the "all clear" by the authorities.

Tornadoes are spawned by thunderstorms and flash flooding can occur with thunderstorms. When a "severe thunderstorm warning" is issued, review what actions to take under a "tornado warning" or a "flash flood warning." Develop an emergency communication plan in case family members are separated from one another during a thunderstorm. Please be aware of hail. Hail is produced by many strong thunderstorms. Hail can be smaller than a pea or as large as a softball and can be very destructive to plants and crops. In a hailstorm, take cover immediately. Pets and livestock are particularly vulnerable to hail, so bring animals into a shelter.

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What is lightning?

Lightning is an electrical discharge that results from the buildup of positive and negative charges within a thunderstorm. When the buildup becomes strong enough, lightning appears as a "bolt." This flash of light usually occurs within the clouds or between the clouds and the ground. A bolt of lightning reaches a temperature approaching 50,000 degrees Fahrenheit in a split second. The rapid heating and cooling of air near the lightning causes thunder. Thunderstorms can bring heavy rains (which can cause flash flooding), strong winds, hail, lightning and tornadoes. In a severe thunderstorm get inside a sturdy building and stay tuned to a battery-operated radio for weather information. Lightning is a major threat during a thunderstorm.

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Precautions to be taken during thunderstorms and lightning

Have disaster supplies on hand. Consult the Disaster Supplies Kit page. Other precautions:

  • Check for hazards in the yard. Dead or rotting trees and branches can fall during a severe thunderstorm and cause injury and damage.
  • Make sure that all family members know how to respond after a thunderstorm.
  • Teach family members how and when to turn off gas, electricity and water.
  • Teach children how and when to call 1-1-9, PMO, fire department, which TV station and which radio station to tune for emergency information.

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What to do during a thunderstorm?
  • If caught indoors:
  • Secure outdoor objects such as lawn furniture that could blow away or cause damage or injury. Take light objects inside. Shutter windows securely and brace outside doors.
  • Listen to a battery operated radio or television for the latest storm information.
  • Do not handle any electrical equipment or telephones because lightning could follow the wire. Television sets are particularly dangerous at this time.
  • Avoid bathtubs, water faucets, and sinks because metal pipes can transmit electricity.
  • If caught outdoors:
  • Attempt to get into a building or car. If no structure is available, get to an open space an squat low to the ground as quickly as possible.
  • If in the woods:
  • Find an area protected by low clump of trees - never stand underneath a single large tree in the open.
  • It is a myth that lightning never strikes twice in the same place. In fact, lightning will strike several times in the same place in the course of one discharge.
  • Be aware of the potential for flooding in low-lying areas.
  • Crouch with hands on knees.
  • Avoid tall structures such as towers, tall trees, fences, telephone lines, or power lines
  • Stay away from natural lightning rods such as golf clubs, tractors, fishing rods, bicycles, or camping equipment
  • Stay away from rivers, lakes, or other bodies of water. If you are isolated in a level field or prairie and you feel your hair stand on end (which indicates that lightning is about to strike), bend forward, putting your hands on your knees. A position with feet together and crouching while removing all metal objects is recommended. Do not lie flat on the ground.
  • If caught in a car:
  • Pull safely onto the shoulder of the road away from any trees that could fall on the vehicle. Stay in the car and turn on the emergency flashers until the heavy rains subside. Avoid flooded roadways.
  • Drive only if necessary. Debris and washed-out roads may make driving dangerous.

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What to do when lightning strikes a person

Check for injuries. A person who has been struck by lightning does not carry an electrical charge that can shock other people. If the victim is burned, provide first aid and call emergency medical assistance immediately. Look for burns where lightning entered and exited the body. If the strike cause the victim's heart and breathing to stop, give cardiopulmonary resuscitation (CPR) until medical professionals arrive and take over.

Remember to help your neighbors who may require special assistance--infants, elderly people, and people with disabilities. Report downed utility wires.

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