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The science behind thunderstorms

August 20, 2018

Temperatures across the UK have recently been at a 5-year high, which begs the question, how long will this heatwave last?

With all the sticky summer sun we’ve been having, it was only a matter of time before we saw cracks of lightning and heard the rumble of thunder.

As we enjoy the respite brought by recent downpours, we’ve decided to explore the science of thunderstorms.

How does a thunderstorm develop?

For a thunderstorm to develop, moisture and rapidly rising warm air must be present. These elements are usually rare in the UK, but the recent soaring temperatures and high humidity has created the perfect condition for thunderstorms to thrive.

But how do these conditions culminate in a thunderstorm?

If the lowest layer of air in the atmosphere is humid, the upper layer of air exceptionally cold, or often both, the air mass becomes unstable. This instability leads to the formation of a tall convective cloud, better known as a thunderstorm.

As near-surface air rises in an unstable air mass it expands and cools. This makes it warmer than its environment, and so the rising continues to increase.

The increasing humidity results in an increase of water vapour present, which condenses into a cloud. This cloud has the ability to release heat, which adds to the warmth of the existing air mass, causing it to rise again within the atmosphere.

Even in tropical locations, the top part of a thunderstorm will consist of ice, ice graupel, snow and even hail. Approximately 50% of thunderstorm rain is a result of the ice present in the upper portion of a thunderstorm.

Why are thunderstorms important?

Thunderstorms are needed to stabilise the atmosphere. This occurs through using excess water vapour to cool the lower atmosphere, warming the upper atmosphere.

Is lightning needed for a storm to be classed as a thunderstorm?

The answer is yes. Lightning is caused when liquid and ice particles above the freezing level collide, resulting in large electrical fields within the clouds. When these electrical fields reach a big enough size, a giant spark is created, known as lightning.

What time is a thunderstorm most likely to occur?

The most common time for a thunderstorm is the afternoon. This is because the daytime heating of the land by the sun causes the lowest layer of the atmosphere to become unstable.