School was over for the day. Will watched his friends open their umbrellas and head home.
Will had forgotten his umbrella. "It's a good thing Dad can pick me up today.
The weather is terrible!" he thought and sat on a bench in the hallway. "I wonder why."
Will's science class was studying weather, so he started to read the chapter about storms while he waited.
After only a few paragraphs, he fell asleep.
A gust of wind made Will open his eyes. All around him was the wide-open sky!
Glancing down, he realized he was in the basket of a hot air balloon, high above the ground.
Suddenly Will's phone beeped loudly. He pulled QT out of his pocket and said, "Hi! The people down there look like bugs!"
"But they'll get bigger if we start to drop," QT warned.
"Quick, pull the silver handles down to start the burners!"
As soon as Will pulled the handles, huge flames shot out above him.
"I don't want to burn the balloon!" he yelled over the burners' noise, letting go of the handles.
An image of a hot air balloon lit up QT's screen.
"We need the burners to heat the air in the balloon.
Hot air is lighter than the cold air outside the balloon.
That makes the balloon float," QT explained.
"Hot air rising is very powerful. It also creates the weather, you know!"
"Really?" Will asked. "How does it create weather?"
"The sun heats the planet, but some areas get hotter than others.
So the air in the hot regions rises, and cooler air moves in to take its place. We call this air movement wind."
"So that's what makes wind!" Will watched a cloud pass by. "Does hot air make clouds too?"
"Not really. When the sun heats water, some of those particles evaporate.
That means they turn into a gas, called water vapor.
The water vapor rises with the hot air. But the air cools with time.
When it's cold enough, the water vapor condenses, meaning it becomes liquid water again.
But the tiny droplets are so light that they float, forming clouds."
Will pointed to a low, gray cloud in the distance. "That's water?"
"Yes. The cloud looks dark and gray because the water is blocking the sunlight.
That feathery one high above us is actually made of ice crystals, not water, because it's much colder higher up," QT explained.
Gazing at the clouds, Will commented, "I like the ones that look like cotton balls best. Their shapes are always changing."
"That's exactly what makes them dangerous! That harmless-looking, little cloud can quickly become a huge thundercloud, over 12,000 meters tall!
Look to your left, and you'll see what I mean."
Will turned and saw a tall, dark cloud in the distance. "Wow! That's huge."
An image of a cloud appeared on QT's screen.
"Thunderclouds form when there's a lot of warm, humid air.
First a puffy, little cloud appears, like that one.
If the cloud stays warmer than the air around it, it grows taller; warm air keeps moving up and up.
The water droplets combine with other droplets until they get too big and heavy. Then they fall to the ground.
Snow and hail also fall when they get too heavy," QT explained.
"It's raining over there! I hope we don't get wet," Will said. "What makes it snow?"
"Snowflakes form when a cloud's temperature is below freezing, so water vapor turns directly into ice without becoming drops of water first.
The ice crystals give each snowflake a unique shape," QT answered.
"Hail is another kind of precipitation. It forms in thunderclouds.
Water droplets are carried by wind from warmer parts of the cloud into colder parts.
The droplets freeze, and when they fall back through the warm parts of the cloud,
the little balls of ice are covered by a layer of water condensing around them.
If another wind carries the ice up again, that layer will freeze, making the hail bigger.
After many cycles of this, hail can become as big as a baseball!"
"I hope that thundercloud doesn't create such big hail," Will muttered, nervously watching the dark cloud. "It's coming this way!"
"We'd better land. We don't want to be up here if that cloud produces lightning!
Pull on that cord to release some hot air," QT instructed.
Will pulled on the cord, and a vent at the top of the balloon opened. They began to descend slowly.
"What causes lightning?" Will asked.
"Well, when rain starts to fall from a thundercloud, it pulls some air down with it.
The falling air and water rubs against the rising air and water, which creates electric charges.
Lightning allows this energy to flow. The same basic thing happens when you touch a metal doorknob and feel a shock."
Suddenly a lightning bolt escaped from the cloud, and thunder soon followed.
Will tried not to seem scared, asking, "Why do we usually hear thunder after lightning?"
"When lightning strikes, it heats the air around it to thirty thousand degrees Celsius!
That makes the air expand very quickly.
As it expands, it pushes the air around it, which creates a sound wave—thunder.
We see lightning first because light travels much faster than sound."
"I heard that you can measure how far away lightning is by counting the seconds between the lightning and thunder.
If three seconds pass, the lightning struck about a kilometer away," Will said.
"That's right, but we're almost to the ground! Get ready to land!"
Will grabbed the side of the basket and closed his eyes. The basket shook as it touched the ground.
Will opened one eye and saw his dad standing over him, gently shaking his shoulder. "Time to go, sleepyhead," he said.
"I hope it's still storming," Will said as he got up. "Storms are really amazing, Dad!"