Squeaks and I were out on a walk this morning, and we both noticed lots of things are changing!

We found leaves that had changed color and fallen to the ground, and we saw birds flying south for the winter. What else did you observe, Squeaks? [Squeaks squeaks].

Squeaks says that he found something all over the plants this morning, something frozen and sparkling. Hmm. Was it cold, and just lightly covering the plants? [Squeaks squeaks].

Squeaks, it sounds like you found frost. That’s a layer of ice that can freeze over things like plants, windows, and even spiderwebs. It only happens at certain times of the year, and it can be a special treat that shows us our seasons in action.

During fall and spring, the weather is changing from hot to cold, or from cold to hot, which is perfect for frost. During the day, temperatures are warm enough that the air can hold onto a bit of water vapor, which is water that’s spread out through the air as an invisible gas. But then, as night falls and the air gets colder, the gas turns into liquid water again.

That’s why sometimes when you go outside in the morning the grass is wet, even if it hasn’t rained. The water on the grass actually comes from the air. There’s a special name for when water in the air turns into a liquid like this.

It’s called condensation. The water vapor touching things like grass or windows condenses, leaving tiny drops of water over everything. If it’s only a little cold, the water on the grass will stay the way it is, making the ground and plants a bit wet in the morning.

But when the weather is just right, which is when it’s warm during the day and can get very cold at night, the water changes one more time: it freezes into ice! That ice is what we call frost, and it happens when the temperature at night is below 0 degrees. Celsius, or 32 degrees Fahrenheit.

Frost usually won’t make ice over the entire surface of a leaf it freezes on. Instead, water freezes in the shape of the small drops it first made, so it looks like little delicate freckles of ice polka-dotting the whole leaf. Once morning comes, you can walk outside and see beautiful, frozen frost on everything.

It can sparkle in the bright sunlight, but it won’t last for long. What do you think will happen to the frost, Squeaks? [Squeaks squeaks]. That’s a good observation, Squeaks.

It does look like the frost just disappears. But the frost is actually changing again. Later in the morning, as the sun warms up the space around it, the frost starts to melt.

The ice might turn back into liquid water, or if it warms up enough very quickly, it can even turn right back into water vapor in the air. Sometimes, you can even see the water vapor rising right off of the ground. It looks just like a thick fog coming up.

Frost can be beautiful to see, and it’s usually a sign that the seasons and weather are changing. When we’re going from the warm summer to the cold winter, frost means fall is here, and the air and soil are about to get very chilly. People who grow plants, like farmers and gardeners, pay very close attention to the temperatures in fall to help keep their plants from freezing in the morning frost.

Some farmers that work in places where there’s lots of frost need to make sure to pick all of their crops before fall gets too cold. They’ll check things like how much water is in the air, the temperature during the day and at night, and how fast the wind is going, all so they can know when the first big frost of the year will happen. It’s like they’re water scientists!

You can be a frost-watching expert, too! You could try checking the weather before bed to see how cold it will get during the night, and guess whether there might be frost in the morning. Is the air above freezing before bed, but going to drop down below freezing overnight?

Is it humid, with lots of water vapor in the air? Make your guess, then look at the ground outside the next morning to see if you were right! [Squeaks squeaks]. Sure, we can try it tonight, Squeaks!

We’ll make a field journal where we can write everything down to keep track. If you try this, too, Squeaks and I would love to hear about what you learned! Just ask a grown-up to help you go to our website at patreon.com/scishowkids, where you can tell us about your results.

Thanks, and we’ll see you next time here at the Fort!