Thunderstorms

• Thunderstorms (PDF Version -- 857KB)

Thunderstorms are very common and affect great numbers of people each year. Despite their small size in comparison to hurricanes and winter storms, all thunderstorms are dangerous. Every thunderstorm produces lightning. Other associated dangers of thunderstorms include tornadoes, strong winds, hail, and flash flooding. Flash flooding is responsible for more fatalities - more than 140 annually - than any other thunderstorm- associated hazard.

Some thunderstorms do not produce rain that reaches the ground. These are generically referred to as dry thunderstorms and are most prevalent in the western United States. Known to spawn wildfires, these storms occur when there is a large layer of dry air between the base of the cloud and the ground. The falling raindrops evaporate, but lightning can still reach the ground.

What to do before thunderstorms approach

1. Know the terms used by weather forecasters:
   • Severe Thunderstorm Watch - Tells you when and where severe thunderstorms are likely to occur. Watch the sky and stay tuned to radio or television to know when warnings are issued.
   • Severe Thunderstorm Warning - Issued when severe weather has been reported by spotters or indicated by radar. Warnings indicate imminent danger to life and property to those in the path of the storm.
     
     
2. Know thunderstorm facts:
   • Thunderstorms may occur singly, in clusters, or in lines.
   • Some of the most severe weather occurs when a single thunderstorm affects one location for an extended time.
   • Thunderstorms typically produce heavy rain for a brief period, anywhere from 30 minutes to an hour.
   • Warm, humid conditions are very favorable for thunderstorm development.
   • A typical thunderstorm is 15 miles in diameter and lasts an average of 30 minutes.
   • Of the estimated 100,000 thunderstorms each year in the United States, about 10 percent are classified as severe.
   • A thunderstorm is classified as severe if it produces hail at least three-quarters of an inch in diameter, has winds of 58 miles per hour or higher, or produces a tornado.
     
     
3. Know the calculation to determine how close you are to a thunderstorm:
• Count the number of seconds between a flash of lightning and the next clap of thunder. Divide this number by 5 to determine the distance to the lightning in miles.
  
  
4. Remove dead or rotting trees and branches that could fall and cause injury or damage during a severe thunderstorm.
   
   
5. When a thunderstorm approaches, secure outdoor objects that could blow away or cause damage. Shutter windows, if possible, and secure outside doors. If shutters are not available, close window blinds, shades, or curtains.

Lightning

The ingredient that defines a thunderstorm is lightning. Since lightning creates thunder, a storm producing lightning is called a thunderstorm. Lightning occurs during all thunderstorms.

Lightning results from the buildup and discharge of electrical energy between positively and negatively charged areas.

The unpredictability of lightning increases the risk to individuals and property. In the United States, an average of 300 people are injured and 80 people are killed each year by lightning. Although most lightning victims survive, people struck by lightning often report a variety of long-term, debilitating symptoms, including memory loss, attention deficits, sleep disorders, numbness, dizziness, stiffness in joints, irritability, fatigue, weakness, muscle spasms, depression, and an inability to sit for a long period of time.

When thunderstorms threaten your area, get inside a home, building or hard top automobile (not a convertible) and stay away from metallic objects and fixtures.

1. If you are inside a home:
   • Avoid showering or bathing. Plumbing and bathroom fixtures can conduct electricity.
   • Avoid using a corded telephone, except for emergencies. Cordless and cellular telephones are safe to use.
   • Unplug appliances and other electrical items such as computers and turn off air conditioners. Power surges from lightning can cause serious damage.
   • Use your battery operated NOAA Weather Radio for updates from local officials.
     
     
2. If outside, with no time to reach a safe location, follow these recommenations:
   • In a forest, seek shelter in a low area under a thick growth of small trees.
   • In open areas, go to a low place such as a ravine or valley. Be alert for flash floods.
   • Do not stand under a natural lightning rod, such as a tall, isolated tree in an open area.
   • Do not stand on a hilltop, in an open field, on the beach or in a boat on the water.
   • Avoid isolated sheds or other small structures in open areas.
   • Get away from open water. If you are boating or swimming, get to land and find shelter immediately.
   • Get away from anything metal— tractors, farm equipment, motorcycles, golf carts, golf clubs and bicycles.
   • Stay away from wire fences, clotheslines, metal pipes, rails and other metallic paths that could carry lightning to you from some distance away.
   • If you feel your hair stand on end (which indicates that lightning is about to strike), squat low to the ground on the balls of your feet. Place your hands over your ears and your head between your knees. Make yourself the smallest target possible and minimize your contact with the ground. DO NOT lie flat on the ground.
     
     
3. Remember the following facts and safety tips about lightning.
• Facts:
• Lightning often strikes outside of heavy rain and may occur as far as 10 miles away from any rainfall.
• Lightning-strike victims carry no electrical charge and should be attended to immediately. If breathing has stopped, begin mouth-tomouth resuscitation. If the heart has stopped, a trained person should administer CPR. If the victim has a pulse and is breathing, look for other possible injuries. Check for burns where the lightning entered and left the body. Be alert also for nervous system damage, broken bones, and loss of hearing or eyesight. Contact your local emergency management office or American Red Cross chapter for information on CPR and first aid classes.
• “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!
• Most lightning deaths and injuries occur when people are caught outdoors in the summer months during the afternoon and evening. • Many fires in the western United States and Alaska are started by lightning. • Lightning can occur from cloudto- cloud, within a cloud, cloud-toground, or cloud-to-air.
• Your chances of being struck by lightning are estimated to be 1 in 600,000 but could be even less by following safety tips.
  
  
• Safety Tips:
• Postpone outdoor activities if thunderstorms are likely.
• Remember the 30/30 lightning safety rule - Go indoors if, after seeing lighting, you cannot count to 30 before hearing thunder. Stay indoors for 30 minutes after hearing the last clap of thunder.
• Rubber-soled shoes and rubber tires provide NO protection from lightning. However, the steel frame of a hardtopped 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