Thunderstorm facts
Thunderstorm: a storm accompanied by lightning and thunder.
-- Merriam-Webster Dictionary

Severe Thunderstorm: a thunderstorm that contains hail that is three quarter of an inch or the wind gusts are at 58 mph or higher.
-- National Weather Service, United States

A thunderstorm is defined as a storm that contains lightning and thunder, which are caused by unstable atmospheric conditions. When the cold upper air sinks and the warm moist air rises, storm clouds or 'thunderheads' develop, resulting in thunderstorms. This can occur singularly, in clusters, or in lines. Severe thunderstorms can bring with them heavy rains, which can cause flash floods, strong winds, lightning, hail, and even tornadoes.

The type of clouds that are usually responsible for thunderstorms are called cumulonimbus (a Latin word which translates into 'rain heaps'). These types of clouds can span the entire troposphere, and can be more than 12 miles high. During extreme storms, the up-drafts can reach as high as 100 mph, while the down-drafts can be even higher.

Facts About Thunderstorms

Annually, an estimated 16 million thunderstorms happen across the world.
18,000 thunderstorms occur at any given moment somewhere on the Earth.
Thunderstorms cause 95 - 100 deaths and more than 100 injuries every year around the world.
A typical thunderstorm is about 15 miles in radius and lasts for approximately half an hour. Lightning from a thunderstorm can be witnessed as far as 10 miles away outside its radius.
Lightning from thunderstorms kills more people annually that tornadoes do.

Kampala in Uganda witnesses the most thunderstorms globally - about 240 annually.
Florida witnesses the most thunderstorms in the United States - about 80 to 100 annually.
On a yearly basis, thunderstorms cause about a billion dollars of damage.
In the United States, the costliest thunderstorm ever, caused damage worth $625 million. It affected Denver in Colorado on 11th July, 1990.
Lightning is almost 5 times hotter than the sun's surface.

According to a NASA study, the most intense and powerful thunderstorms occur in the eastern part of the Andes in Argentina.
Thunderstorms, in some cases, produce hail. Hail is frozen raindrops which gather more mass due to continuous down-drafts and increase in size.
Thunderstorms are more likely to occur during spring and summer.
Catatumbo lightning (atmospheric phenomenon) in Venezuela spawns more lightning every year than any other storm.
A bolt of lightning accompanying a thunderstorm can reach temperatures up to 50,000° F.

The coastal deserts of Chile never experience any thunderstorms.
St. Paul Island, near Alaska, has experienced only one officially recorded thunderstorm, - which occurred on 8th November, 1982.
A 1979 hailstorm in Norwich, England, generated ice flakes instead of the usual spherical hail. These were about 2 by 4 inches in size, and fluttered from the sky to the ground like white leaves.
The deadliest hailstorm ever occurred on April 30th, 1888, in the Moradabad and Bareilly districts of India; it killed 246 people.
The costliest hailstorm ever, in terms of damage, took place in Munich, Germany, in 1984. The hailstorm caused damage worth a billion dollars.

The heaviest hailstone ever recorded weighed 2.25 lb, and fell in the Gopalganj district of Bangladesh on 14th April, 1986.
The earliest recorded hailstone calamity occurred in Roopkund (in present day Uttarakhand), India, in the 9th century, in which several hundred Hindu pilgrims died.
Scientific studies suggest that the chances of an individual getting struck by lightning is 1 in 600,000.
Thunderstorms are the most powerful storms in the Earth's atmosphere.
A dying thunderstorm is known to trigger another thunderstorm.

Hail Classification

Thunderstorms are mostly accompanied by hail. The intensity of a hailstorm is judged based on the size of the falling hail. The United States Geological Survey (USGS) has laid down rules and nomenclatures to classify hail.

Size of Hail
(in inches)
0.25 Pea
0.50 Marble
0.75 Penny/Dime
0.88 Mothball/Nickel
1.00 Quarter
1.25 Half Dollar
1.50 Walnut
1.75 Golfball
2.00 Hen Leg
2.50 Tennis Ball
2.75 Baseball
3.00 Tea Cup
4.00 Grapefruit
4.50 Soft Ball
4.75 Melon
5.00 Computer CD
6.50 Cantaloupe
7.00 Phonograph Record
8.00 Volleyball
8.25 Bowling Ball

Thunderstorms are capable of causing extensive damage to both life and property. You need to be very careful, especially if you live in an area where thunderstorms are common. Make sure that you and your family are well-prepared and have a definite idea as to where to stay during severe storms. Seeking shelter under a tree should be avoided, as the wind gusts can uproot trees or break old branches, causing injury or even death. Avoid standing close to lamp posts and street lights, and avoid using electric appliances during a thunderstorm. Stay safe, stay calm, and let the thunder roll on.