United States Search and Rescue Task Force

Thunderstorms

The key ingredient that defines a thunderstorm is lightning.   Since lightning creates thunder, a storm with lightning is called a thunderstorm.

Thunderstorms occur when large air masses rise quickly into the atmosphere, forming huge cumulonimbus clouds.  Severe air currents inside the clouds cause water droplets and ice crystals to crash into one another continually, and the friction between these particles creates static electricity in the cloud.  Over time, opposite charges build between the top and bottom of the cloud, and the bottom of the cloud and the earth.  When these opposing charges become intense, a gigantic spark occurs (lightning) which jumps the gap between the cloud and the earth.  The thunder accompanying lightning is the noise produced by the discharge.

What is Lightning?

• The action of rising and descending air within a thunderstorm separates positive and negative charges. Water and ice particles also affect the distribution of electrical charge.
• Lightning results from the buildup and discharge of electrical energy between positively and negatively charged areas.
• The average flash could light a 100-watt light bulb for more than 3 months.
• Most lightning occurs within the cloud or between the cloud and ground.
• Your chances of being struck by lightning are estimated to be 1 in 600,000 but could be reduced by following safety rules.
• Most lightning deaths and injuries occur when people are caught outdoors.
• Most lightning casualties occur in the summer months and during the afternoon and early evening.
• The air near a lightning strike is heated to 50,000øF hotter than the surface of the sun! The rapid heating and cooling of air near the lightning channel causes a shock wave that results in thunder.
• Many fires in the western United States and Alaska are started by lightning. In the past decade, over 15,000 lightning-induced fires nationwide have resulted in several hundred million dollars a year in damage and the loss of 2 million acres of forest.

In recent years, people have been killed by lightning while:

boating
standing under a tree
playing soccer
swimming
riding on a lawnmower
fishing in a boat
golfing
talking on the telephone
mountain climbing
bike riding
loading a truck

Which way does lightning travel?

A cloud-to-ground lightning strike begins as an invisible channel of electrically charged air moving from the cloud toward the ground. When one channel nears an object on the ground, a powerful surge of electricity from the ground moves upward to the cloud and produces the visible lightning strike!

Lightning Myths and Facts

MYTH: If it is not raining, then there is no danger from lightning.
FACT: Lightning often strikes outside of heavy rain and may occur as far as 10 miles away from any rainfall.

MYTH: The rubber soles of shoes or rubber tires on a car will protect you from being struck by lightning.
FACT: Rubber-soled shoes and rubber tires provide NO protection from lightning. However, the steel frame of a hard-topped vehicle provides increased protection if you are not touching metal. Although you may be injured if lightning strikes your car, you are much safer inside a vehicle than outside.

MYTH: People struck by lightning carry an electrical charge and should not be touched.
FACT: Lightning-strike victims carry no electrical charge and should be attended to immediately. Contact your local American Red Cross chapter for information on CPR and first aid classes.

MYTH: "Heat lightning" occurs after very hot summer days and poses no threat.
FACT: What is referred to as "heat lightning" is actually lightning from a thunderstorm too far away for thunder to be heard. However, the storm may be moving in your direction!

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.

BEFORE

Learn the thunderstorm danger signs

• Dark, towering, or threatening clouds.
• Distant lightning and thunder.

Have disaster supplies on hand

• Flashlight with extra batteries
• Portable, battery-operated radio and extra batteries
• First aid kit and manual
• Emergency food and water
• Nonelectric can opener
• Essential medicines
• Cash and credit cards
• Sturdy shoes

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 9-1-1, police, fire department, and which radio station to tune for emergency information.

Severe Thunderstorm Watches and Warnings:

A severe thunderstorm watch is issued by the National Weather Service 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 television for more information.

A severe thunderstorm warning is issued when a severe thunderstorm has been sighted or indicated by weather radar. At this point, the danger is very serious and everyone should go to a safe place, turn on a battery-operated radio or television, and wait for the "all clear" by the authorities.

Learn how to respond to a tornado and flash flood.
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 (a real possibility during the day when adults are at work and children are at school), have a plan for getting back together.

Ask an out-of-state relative or friend to serve as the "family contact". After a disaster, it's often easier to call long distance. Make sure everyone knows the name, address, and phone number of the contact person.

Contact you local emergency management office or American Red Cross chapter for more information on thunderstorms and lightning.

DURING

If 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 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.) 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 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 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.

Estimating the Distance from a Thunderstorm:

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.

Important: You are in danger from lightning if you can hear thunder. Knowing how far away a storm is does not mean that you're in danger only when the storm is overhead.

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.

AFTER

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.

Drive only if necessary. Debris and washed-out roads may make driving dangerous.

Mitigation:
Mitigation includes any activities that prevent an emergency, reduce the chance of an emergency happening, or lessen the damaging effects of unavoidable emergencies. Investing in preventive mitigation steps now, such as installing lightning rods to carry the electrical charge of lightning bolts safely to the ground or purchasing flood insurance, will help reduce the impact of severe thunderstorms in the future.