A thunderstorm is a storm with lightning and thunder. Lightning causes thunder, that loud crashing noise you hear. 

A typical thunderstorm has a short period of heavy rain that lasts anywhere from 30 minutes to an hour. Thunderstorms happen in every state. Nearly 1,800 thunderstorms are happening at any moment around the world. That's 16 million a year!

Not all thunderstorms produce rain that reaches the ground. These dry thunderstorms are most common across the western USA and often start wildfires. These storms often form high above the ground with a large layer of very dry air between the base of the cloud and the ground. As rain falls from the cloud into the dry air, the rain drops evaporate before they reach the ground. 

Thunderstorms affect small areas when compared with hurricanes and winter storms. The typical thunderstorm is 15 miles in diameter. 

When a streak of lightning flashes across the sky, a crack of thunder is often heard several seconds later. Thunder happens because lightning heats the air to more than 43,000 degrees, causing the air to expand (move outward). As this air cools, it begins to contract (move inward). This quick expansion and contraction of air around the lightning starts air molecules moving back and forth, making sound waves, which we hear as thunder.

You can estimate how many miles away a storm is by counting the number of seconds between the flash of lightning and the clap of thunder. Divide the number of seconds by five to get the distance in miles. The lightning is seen before the thunder is heard because light travels faster than sound. (Of course, get safe shelter first, before you take the time to count the seconds!)

Thunder won't hurt you, but lightning will! Lightning can strike people and buildings and is very dangerous. So it's important to pay attention when you hear thunder. Though the chances of being struck by lightning are estimated at 1 in 700,000, these huge electrical sparks are one of the leading causes of weather-related deaths in the USA each year, with an average of 73 people killed.

Despite their small size, all thunderstorms are dangerous. Lightning kills more people each year than tornadoes. Heavy rain from thunderstorms can lead to flash flooding. Strong winds, hail, and tornadoes are also dangers associated with some thunderstorms. 

Thunderstorms need three things: 

  • Moisture:  to form clouds and rain. 
  • Unstable Air:  relatively warm air that can rise rapidly. 
  • Lift:  fronts, sea breezes and mountains are capable of lifting air to help form thunderstorms. 

Thunderstorms are most likely to occur in the spring and summer months and during the afternoon and evening hours, but they can occur year-round and at all hours of the day or night. Along the Gulf Coast and across the southeastern and western states, most thunderstorms occur during the afternoon. Thunderstorms often occur in the late afternoon and at night in the plains states. Thunder and lightning can sometimes even come with snowstorm! During the blizzard of March 1993, lightning resulted in power outages near Washington, D.C.

Did You Know...

  • Lightning can strike in the same place more than once!
  • Lightning can strike without rain. Sometimes it can be up to ten miles away from the rain!
  • Rubber-soled shoes and rubber tires provide NO protection from lightning. You are much safer inside a vehicle than outside during a thunderstorm.
  • Sometimes you see lightning, but don't hear thunder. That is because the lightning is far away from you.
  • The average flash of lightning could turn on a 100-watt light bulb for more than 3 months.
  • The air near a lightning strike is hotter than the surface of the sun! 
  • In the past 10 years, more than 15,000 fires have been started by lightning.
Thunderstorm Pictures

NOAA Photo Library
FEMA For Kids