by Nicole Gadda
Most of us who have lived through a North Carolina summer have experienced a thunderstorm. Think of those hot, humid days where the sun is beating down without a cloud in the sky. You can hear the sounds of cicadas chirping and the laughter of kids outside on summer recess. Suddenly, BOOM! Dark, ominous clouds suddenly roll in, heavy rain begins to pellet the ground, lightning flashes, and thunder reverberates the air. And almost as quickly as it started, the rain begins to lighten, the clouds roll away, and the sun is shining again. How do thunderstorms occur so suddenly? And why do thunderstorms happen in the first place?
Thunderstorms are weather events that produce rain, lightning, and thunder. Severe thunderstorms can produce hail, tornadoes, strong winds, and flash flooding. Thunderstorms form in three stages: (1) the developing stage, where storm clouds form, (2) the mature stage, where the thunderstorm is fully formed and active, and (3) the dissipating stage, where the storm weakens and ends.
The developing stage occurs when warm, moist air (like the air on a hot, muggy summer day) rises into the atmosphere. Because air in the atmosphere is cooler than air closer to Earth, the warm air cools as it rises. The water vapor present in the air forms liquid water droplets in a process called condensation, creating puffy cumulus clouds. Similar to how the bubbles in a boiling pot of water rise from the bottom of the pot to the top, the cloud will continue to grow as long as warm air from below rises. Once the air is fully cooled, it drops lower in the atmosphere, where it warms up and rises again. This cycle of rising and falling air is called a “convection cell.” Thunderstorms can form a single convection cell, or multiple convection cells can group together and create a severe storm, with strong winds and tornadoes possible. Whether a convection cell results in a cloud or a thunderstorm depends on the volume of air and moisture. Smaller volumes lead to cloud formation, whereas larger volumes lead to thunderstorms. This is why thunderstorms are more common in the summer – the heavy humidity (which is a measurement for the amount of water vapor in the air) results in more water vapor condensing into liquid water droplets. Similarly, summer storms seem like they happen out of nowhere because of the intensity of the summer sun. In the summer, Earth is tilted closer to the sun, which results in warmer weather. Because the Earth is closer to the sun, the air heats up faster and rises into the atmosphere where it creates convection cells. The heat + humidity = the perfect equation for a spontaneous storm!
As a cloud gets larger and heavier, and more water vapor from the rising air condenses into liquid, the cloud begins to look dark and gray. When the rising air can no longer support the weight of the cloud, raindrops start to fall, marking the start of the mature stage. Cool, dry air (a downdraft) flows downward as warm, moist air (an updraft) flows upward in the cloud. Have you ever rubbed your feet on the carpet back and forth fast enough to create a shock? Similarly, the moving air within the cloud builds up electric charges as it slides past air moving in the opposite direction. This buildup of energy creates lightning that strikes the earth. Lightning can heat the air around it to 54,000°F! This extreme heating causes the air to expand, creating a shock wave that turns into a booming sound that’s better known as thunder. The “BOOM!” and “crackle!” that we hear after seeing a bolt of lightning is the sound of lightning itself. The reason we hear it a few seconds after seeing a bolt of lightning is because sound travels slower than light.
The thunderstorm enters the dissipating stage when the thunderstorm starts to weaken. This occurs once the downdrafts are stronger than the updrafts. As a result, rain gets lighter, the electrical charges that cause lightning disappear, and the clouds fade away, revealing the sun and sky again.
In the United States, most thunderstorms occur along the Gulf Coast and across southeastern and western states during the spring and summer months; however, no place is completely safe from the threat of severe storms. As you’re reading this, there are likely 2,000 thunderstorms happening right now across the world! So, the next time a thunderstorm rolls in while you’re enjoying a hot, summer day in the pool, at least you’ll know you’re not alone while you wait for the storm to pass.
