68 Thunderstorms-High

Thunderstorms FOCUS Question What causes thunderstorms?

A Dark and Stormy Night Zap! Lightning streaks across the sky. Boom! Thunder rattles the windows. A thunderstorm can be exciting, but it can also be dangerous. Heavy rain can cause floods. Lightning can strike houses, trees, and even people. Thunderstorms start out like any other rainstorm. The Sun warms up moist air near the ground. The warm air rises and sends water vapor toward the sky. High in the sky, the vapor cools and condenses into tiny water droplets to form a cloud. But unlike common rain clouds, thunderclouds grow tall and develop electrical charges. Here's how it works.

A Charged-Up Cloud A thundercloud begins to form when warm, moist air rises into the sky. The rising air creates an updraft. Near the top of the cloud, the air is cold. This cold air is heavy, so it sinks through the cloud, creating a downdraft. Water droplets that have turned to ice also fall through the cloud. Meanwhile, more warm, moist air rises up. The cloud grows taller and becomes a thundercloud, or cumulonimbus cloud. As the updraft and downdraft move within the cloud, dust, water droplets, and ice bump into each other. These particles rub together and become electrically charged.

It's Electrifying! Have you ever felt a shock after walking across a rug in your socks? That shock is a tiny zap of static electricity. Lightning is a much bigger zap. In a thundercloud, positive electrical charges build up near the top. Negative charges build up in the middle and near the bottom of the cloud. Just like in a magnet, positive and negative charges attract each other. Lightning happens when a group of negative charges jump toward the positive charges. Lightning can occur within a cloud, or it can move from one cloud to another cloud. It can also spark between a cloud and the ground.

Bolt and Boom! Lightning is almost always followed by thunder. That loud clap happens because lightning releases a lot of energy. The air near the bolt becomes extremely hot, making it suddenly expand. As the air quickly cools, it contracts. This collapsing air makes a boom that we hear as thunder. Light travels much faster than sound. If lightning strikes nearby, you will hear a loud crack of thunder at the same moment you see the flash. If lightning strikes in the distance, you will see it right away, but the thunder will rumble a few seconds later. Math Moment Each second between seeing lightning and hearing thunder represents about 300 meters (984 ft.) between you and the bolt. How far away is the bolt if you count 5 seconds between the flash and the boom?

Types of Thunderstorms A towering thundercloud is also called a cell. Single cell thunderstorms create short bursts of rain with a lot of wind and some lightning. A storm with just one cell won't last long. When single cells join together, a multicell storm forms. Multicell thunderstorms can be very strong and last for a long time. As one cell begins to die down, another cell gains strength, dropping even more rain and producing more lightning. The strongest type of thunderstorm comes from a supercell. Supercells happen when the strong updraft twists inside the cell. Supercells are rare and can lead to tornadoes.