Thunderstorms kill approximately 200 people in the United States and injure about 550 Americans per year, mostly from lightning strikes. Have you heard the common misconception that lightning doesnt strike the same place twice? In fact, lightning strikes the New York Citys Empire State Building about 100 times per year (Figure 1.5). Lightning strikes some places many times a year, such as the Eiffel Tower in Paris.



Thunderstorms are extremely common. Worldwide there are 14 million per year thats 40,000 per day! Most drop a lot of rain on a small area quickly, but some are severe and highly damaging.

thunderstorm formation

Thunderstorms form when ground temperatures are high, ordinarily in the late afternoon or early evening in spring and summer. The two figures below show two stages of thunderstorm buildup (Figure 1.1). Click image to the left or use the URL below. URL: (a) Cumulus and cumulonimbus clouds. (b) A thunderhead.



As temperatures increase, warm, moist air rises. These updrafts first form cumulus and then cumulonimbus clouds. Winds at the top of the troposphere blow the cloud top sideways to make the anvil shape that characterizes a cloud as a thunderhead. As water vapor condenses to form a cloud, the latent heat makes the air in the cloud warmer than the air outside the cloud. Water droplets and ice fly up through the cloud in updrafts. When these droplets get heavy enough, they fall. A mature thunderstorm with updrafts and downdrafts that reach the ground. This starts a downdraft, and soon there is a convection cell within the cloud. The cloud grows into a cumulonimbus


the end

The downdrafts cool the air at the base of the cloud, so the air is no longer warm enough to rise. As a result, convection shuts down. Without convection, water vapor does not condense, no latent heat is released, and the thunderhead runs out of energy. A thunderstorm usually ends only 15 to 30 minutes after it begins, but other thunderstorms may start in the same area.

severe thunderstorms

With severe thunderstorms, the downdrafts are so intense that when they hit the ground, warm air from the ground is sent upward into the storm. The warm air gives the convection cells more energy. Rain and hail grow huge before gravity pulls them to Earth. Severe thunderstorms can last for hours and can cause a lot of damage because of high winds, flooding, intense hail, and tornadoes.

squall lines

Thunderstorms can form individually or in squall lines along a cold front. In the United States, squall lines form in spring and early summer in the Midwest, where the maritime tropical (mT) air mass from the Gulf of Mexico meets the continental polar (cP) air mass from Canada (Figure 1.3). Cold air from the Rockies collided with warm, moist air from the Gulf of Mexico to form this squall line.


lightning and thunder

So much energy collects in cumulonimbus clouds that a huge release of electricity, called lightning, may result (Figure 1.4). The electrical discharge may be between one part of the cloud and another, two clouds, or a cloud and the ground. Lightning heats the air so that it expands explosively. The loud clap is thunder. Light waves travel so rapidly that lightning is seen instantly. Sound waves travel much more slowly, so a thunderclap may come many seconds after the lightning is spotted. Lightning behind the town of Diamond Head, Hawaii.


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thunderstorms are

a) a rare event.

b) rare except in a few places.

-->  c) common in many places.

d) nearly constant everywhere on earth.

energy that collects in cumulonimbus clouds release electricity called

a) thunder

-->  b) lightning

c) static

d) none of the above

lightning never strikes twice.

a) true

-->  b) false

sound waves travel more slowly, so thunder may come many seconds after lightning.

-->  a) true

b) false

thunderstorms most commonly occur

-->  a) when ground temperatures are high compared to the air temperature.

b) in summer and fall.

c) in the early to mid-morning.

d) all of these.

for a thunderstorm to grow

a) warm, moist air creates updrafts forming cumulus and then cumulonimbus clouds form.

b) high winds blow the cloud into an anvil shape.

c) latent heat from the condensation of water vapor makes the cloud warmer than the air outside it, creating heavy updrafts.

-->  d) all of these.

lightning may discharge between

a) parts of two different clouds.

b) two clouds.

c) between a cloud and the ground

-->  d) all of the above

a thunderstorm will end when

a) all the moisture has rained out of the cloud.

b) all the electrical charge in the cloud has been neutralized.

-->  c) downdrafts cool the base of the cloud and shut down convection.

d) all of the above

what causes a severe thunderstorm?

-->  a) intense downdrafts hit the ground and shoot warm air back up into the cloud.

b) there is more moisture in the cloud so the storm can last longer.

c) the electrical charge is more intense due to the squall line.

d) all of the above

what causes thunder?

a) downdrafts in the cloud are drawn down so rapidly that the air collapse behind them.

-->  b) lightning heats the air so that it expands explosively.

c) lightning is light and sound waves that travel at different speeds.

d) none of these.

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