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A thunderstorm develops in an unstable atmosphere when warm moist air near the Earth’s surface rises quickly and cools. The moisture condenses to form rain droplets and dark thunderclouds called cumulonimbus clouds. These storms are often accompanied by hail, lightning, high winds, heavy rain, and tornadoes. Thunderstorms are usually over in an hour although a series of thunderstorms can last for several hours.


Hail forms when updrafts in thunderclouds carry raindrops upwards into extremely cold areas of the atmosphere. The raindrops freeze and are bounced around in the powerful winds within a thunderstorm while new layers of ice are added. Eventually, the hailstones grow too heavy to be supported by the updrafts and fall to the ground. Some hailstones are the size of peas, while others can be as big as grapefruits.


Refer to the lightning page for further information.


Refer to the tornadoes page for further information.

The following are suggestions to follow during a thunderstorm:


  • Stay away from doors and windows.
  • DO NOT use a corded telephone, except in an emergency. Cordless and cellular telephones are safer to use.
  • Take off headsets.
  • Turn off, unplug and stay away from appliances, computers, power tools, and televisions. Power surges from lightning can cause serious damage.
  • Avoid showering or bathing. Plumbing and bathroom fixtures can conduct electricity.


  • Take shelter, preferably in a building. Failing this, take shelter in a depressed area such as a ditch or a culvert. Never take shelter under a tree.
  • In heavy rain, be on the lookout for flash floods.
  • Do not ride bicycles, motorcycles, or golf carts. Do not use metal shovels or golf clubs, as they conduct electricity.


  • Keep a watchful eye to changes in the weather.
  • Carry a portable weather radio.
  • If a thunderstorm watch/warning has been issued, consider postponing any outdoor activities.
  • Remember the 30 – 30 lightning safety rule: go indoors if, after seeing lightning, you cannot count to 30 before hearing thunder. Stay indoors for 30 minutes after the last clap of thunder.
  • Rubber soled shoes and rubber tires provide NO protection from lightning. The steel frame of a hard topped vehicle does provide 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.

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