What is a
A thunderstorm is a
storm where you hear thunder and see lightning. Usually there is
heavy rain in a thunderstorm. Thunderstorms are electric
When there is about to
be a thunderstorm, a cumulonimbus cloud forms, often in a clear blue
sky. (When a cloud’s name ends in nimbus, it means rain or snow is falling from the cloud.) The cloud increases
in size and begins to build up peaks, which become very dark.
Cumulonimbus clouds mean
that there is going to be a thunderstorm, with wind, rain and even hail on a summer day.
The loud sound that
thunder makes is due to the heat of the flash of lightning. This
heat causes the air to suddenly expand (grow bigger) and then contract (grow smaller). The noise we hear is the
sound of this violent expansion and contraction.
The sound of thunder may
go on rolling for several seconds. This is mainly due to echoes
from the ground, from mountains or hills and from buildings.
thunderstorms only in summer?
occur in hot, humid weather so are mostly in summer. There are winter thunderstorms,
however, which occur along the edge of a cold weather front.
The worst thunderstorms
happen in the tropics, where the air can become very hot and very humid. In tropical countries the rainy season often begins with a series of violent
Every day across the
planet Earth there are about 1,800 thunderstorms.
What causes a
· Thunderstorms happen when the air has become very warm
and heavy with water vapour.
· Heated air expands, rises and forms
· When the warm air rising from the ground is very full of
water vapour, it continues to rise and builds up great peaks of cloud.
· Inside this cumulonimbus cloud, a storm is raging as the
warm air rushes in.
· Air pilots know that they must never fly through a
thunder cloud as the force of the winds inside can damage the aircraft.
· When the cloud can support no more water, the rain falls,
very suddenly and heavily.
Why is a
· The air rising to the top of the thunderclouds carry a
negative charge of electricity.
· The raindrops, however, as they begin to fall to the
bottom of the cloud, develop a positive charge of electricity.
· When these charges meet in a violent storm inside the
cloud, electricity is sparked in the form of lightning.
· Every thunderstorm has lightning.
· The upward wind speed inside the cumulonimbus cloud can
reach up to 100 miles per hour.
· The worst thunderstorm area in the world is Kampala, the
capital of Uganda. Kampala has an average of 240 days with thunderstorms every year.
· Severe thunderstorms can produce hailstones of
three-quarters of an inch in diameter (the distance from side to side). A thunderstorm like this can cause terrible damage to
· Never shelter under a tree during a
thunderstorm. Trees can be struck by lightning or have their branches
torn off during a thunderstorm.