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A Moment of Science

Thunderstorms Operate In Cycles

On a summer day, a thunderstorm can appear out of nowhere and disappear just as fast. What causes a storm to change so suddenly?

lightening striking close to homes

Photo: Brian Leon (Flickr)

Storms follow cycles to produce lightening and hail.

On a summer day, a thunderstorm can appear out of nowhere and disappear just as fast. Meteorologists have found that a storm goes through a cycle in which the cloud’s own forces build the storm to its peak and then cause it to subside.

Completing A Cycle

The life cycle of a storm starts inside one of the common, puffy clouds, known as cumulus. To begin with, the cloud is a collection of tiny water droplets.

As warm, moist air rises up through the cumulus cloud and out the top, the water droplets evaporate in the drier air above.

As the air above the cloud gets moister, droplets form at higher and higher altitudes, causing the cloud to grow vertically into the tall anvil-shape associated with thunderstorms.

Updrafts And Downdrafts

As the cloud grows up into the colder air where temperatures are below freezing, the droplets that make up the cloud get larger and larger.

At first they can still be supported by the warm updraft, but when they get too big, they begin to fall, creating a downdraft inside the cloud and rain on the ground.

The updraft and downdraft of air, rain and hail create strong winds and may even help generate lightning and thunder.

Warm To Cold To Warm

Eventually, the cool downdraft forces out the warm, moist air that started the cycle. Without that warm air, the updraft stops and the storm dies out. Sometimes you can feel the cool air from the downdraft at the end of a storm on a hot summer day.

The cycle of a simple storm produced by one cloud can take less than an hour as the cloud’s own precipitation produces a downdraft, cutting off the supply of warm air that started the storm in the first place.

Longer, more violent storms involve numerous clouds, each with its own storm cycle. A group of such storms can occur either together or as a series.

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