Simple Science: How A Thunderstorm Works

With a big red balloon and a watering can, meteorologist Eric Snitil explains how a thunderstorm is created.

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By Eric Snitil

Story Created: Jun 23, 2011 at 11:25 AM AKDT

Story Updated: Jun 24, 2011 at 10:41 AM AKDT


It’s summer, and that means ice cream, baseball, and thunderstorms. Interior portions of Alaska have been dealing with afternoon rumblers since temperatures have begun soaring since spring arrived.

The science behind how a thunderstorm forms can be both simple, and incredibly complex. With simplicity in mind, we’re able to explain how these bad boys form using something as simple as a helium balloon.

There’s s reason we tie those weights to the string of balloons. If we don’t, that balloon takes off toward the sky. How come? The gas inside a helium balloon is less dense than air. The particles within that helium balloon are less compacted together than the air we breathe. Think of it as helium being “lighter” than air. So when we let that balloon go, it rises above the denser air.

Let’s keep that balloon on the ground for a moment by putting a cap on it. That balloon wants to rise, but the cap won’t let it. This is exactly how our atmosphere works.

Temperatures tend to decrease with height in the atmosphere. But occasionally, there’s a layer where temps increase. We call that a capping inversion. We all know that warm air rises and cold air sinks (another reference to density). Warm air will keep rising until it encounters an environment even warmer than itself. In this instance, the atmosphere is “capped”, or quite literally, there’s a ceiling preventing the air underneath from rising.

We need one of two things to get past this problem. One, is called a lifting mechanism- something to physically force the air to rise aside from pure buoyancy. Fronts tend to be a good trigger for this kind of lift. The other can come from our high Alaskan sun angle.

Take Fairbanks in the summer. Temps are cool in the morning, but as the sun rises higher in the sky, temps at the surface begin to warm. The warmer we get, the more unstable, or buoyant that air becomes. We begin to erode away at that cap until eventually - it breaks. Once it breaks, that warm and moist air surges higher into the atmosphere where it cools and condenses, forming clouds and eventually precipitation.

Once that cloud grows to a certain height, varying charges between the atmosphere and ground can generate lightning and thunder. And now we have our thunderstorm!
The audible thunder you hear is the result, in part, of rapid expansion and contraction of air following the near 50,000-degree bolt of lightning. It’s the same reason you hear the pop of a balloon- the highly pressurized air expands rapidly when it pops, creating the noise we all recognize.

It’s pretty amazing how we can duplicate a big thunderstorm in something as small as a balloon.

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