Why Weather? 🌦️

Almost all of Earth's heat comes from the Sun. At night, your side of Earth faces away from the Sun, so it cools off. That's why nights are colder than days.

Winter is colder for a bigger reason: Earth is tilted. When your part of Earth tilts away from the Sun, sunlight hits at a low, slanted angle and spreads out over more ground, so each spot gets less heat. Days are shorter, too, so there's less time to warm up.

🧊 Fun fact: When it's winter in Las Vegas, it's SUMMER in Australia. They're tilted toward the Sun while we're tilted away!

In summer, your part of Earth tilts toward the Sun. The Sun climbs high in the sky, and its light hits the ground almost straight down. The same light is squeezed into a smaller spot, so it heats the ground fast. Days are long, so there's more time to heat up.

Las Vegas gets extra hot because it's a desert: the air is dry and there are few clouds to block the Sun. Dark surfaces like asphalt soak up heat. A parking lot can be 40 degrees hotter than the grass right next to it!

🌡️ Las Vegas summer sidewalks can get hot enough to burn a dog's paws. That's why we walk pets in the morning!

Wind is just air moving from one place to another. Here's the trick: the Sun heats the ground unevenly. Some places (like a hot desert or a blacktop) warm up faster than others (like a lake or the ocean).

Warm air is lighter, so it rises. When it rises, cooler air rushes in underneath to take its place. That rush of air is wind! Air always moves from where there's more of it (high pressure) to where there's less (low pressure). The bigger the difference, the stronger the wind.

🏖️ At the beach, the land heats faster than the water, so cool sea air blows in during the afternoon. That's called a sea breeze.

The Sun warms water in oceans, lakes, and puddles, and some of it turns into an invisible gas called water vapor that floats up (that's evaporation). High in the sky it's cold, so the vapor turns back into tiny droplets (that's condensation). Billions of droplets together make a cloud.

Cloud droplets are so small and light that they float. But they bump into each other and join together. When a drop gets big and heavy enough, the air can't hold it up anymore, and it falls as rain. Then the water flows back to the ocean, and the cycle starts again!

💧 A single raindrop is made of about a MILLION cloud droplets.

Inside a tall storm cloud, ice crystals and water droplets whoosh up and down and bump into each other millions of times. All that rubbing builds up static electricity, like when you shuffle across a carpet and shock your friend, but a BILLION times stronger.

When the charge gets too big, it jumps across the sky as a giant spark: lightning. Lightning is hotter than the surface of the Sun! It heats the air so fast that the air explodes outward, and that boom is thunder.

You see lightning before you hear thunder because light travels much faster than sound. Count the seconds between the flash and the boom, then divide by 5: that's about how many miles away the storm is.

⚡ Safety rule: "When thunder roars, go indoors!"

Hail forms in huge thunderstorm clouds that stretch miles high, where it's freezing cold at the top even in summer. Strong winds inside the cloud, called updrafts, blow raindrops up into the freezing zone, where they turn to ice.

The ice ball falls, picks up more water, gets blown back up, and freezes again. Each trip adds a new layer of ice, like the layers of an onion. When the hailstone gets too heavy for the wind to lift, it falls. The stronger the updraft, the bigger the hail!

🧊 If you cut a hailstone in half, you can count its rings, one for each trip up into the cloud.

Snow starts the same way as rain: with water vapor high in a cold cloud. But when it's below freezing (32°F / 0°C), the vapor doesn't make droplets. It freezes straight into tiny ice crystals.

Water molecules lock together in a pattern with six sides, so every snowflake grows six arms. As a crystal tumbles through the cloud, it grows in its own way, which is why no two snowflakes are exactly alike. For snow to reach the ground, the air has to stay cold all the way down. If it warms up on the way, the snow melts into rain.

🏔️ Las Vegas gets snow about once every few years, but Mount Charleston, just 40 minutes away, gets several feet!

Sunlight looks white, but it's really a mix of every color. When sunlight passes through a raindrop, the drop bends the light (that's called refraction) and bounces it back out. Each color bends a slightly different amount, so the colors spread apart.

Millions of raindrops do this at once, and you see a giant arc of color. To spot a rainbow, the Sun has to be behind you and the rain in front of you. The colors are always in the same order: red, orange, yellow, green, blue, indigo, violet. Remember it with the name ROY G. BIV!

🌈 A rainbow is really a full circle. From an airplane, you can sometimes see the whole thing!