How Do Snowflakes Form? — For Kids

Elementary: The Story in Steps

1. A tiny speck in the sky. High in the sky, there is a tiny bit of pollen or dust. It is very, very small.
2. A drop freezes on the speck. NOAA says a snowflake begins when an extremely cold water droplet freezes onto a pollen or dust speck in the sky.
3. Now there is an ice crystal. That frozen start is an ice crystal. An ice crystal is a tiny piece of ice.
4. The crystal falls and grows. As the ice crystal falls to the ground, water vapor freezes onto it.
5. Six arms grow. The new ice builds the six arms of the snowflake.
6. It keeps six sides. NOAA says the six-sided shape is always kept, even when the arms branch off in new ways.
7. The arms look the same. NOAA says each arm meets the same air as the other arms. So the arms look identical. That means they look just the same.

Why does it have six sides?

NOAA says the ice crystals are patterned. They show the inside order of the crystal.

The water bits in the crystal line up in set spaces. NOAA calls this crystallization. That is how a six-sided snowflake forms.

Warm or cold air can change the shape

NOAA says temperature is the main thing that sets the basic shape. Temperature is how cold or warm the air is.

The wetness of the air matters too, but less. NOAA calls that wetness humidity.

At 23 degrees F, NOAA says we see long crystals like needles.

At 5 degrees F, NOAA says we see very flat crystals like plates.

As a crystal falls, the air can change a little. Then the crystal can grow in a new way. This can happen in minutes. It can even happen in seconds.

Why does each snowflake look its own way?

NOAA asks why no two snowflakes are exactly alike.

NOAA says each snowflake takes a slightly different path from the sky to the ground.

So each one meets slightly different air on the way down.

NOAA says they all tend to look unique. Unique means one of a kind.

They can look like prisms, like needles, or like the lacy pattern many of us know.

Words to know — Elementary

Water vapor: Water in the air. NOAA says water vapor freezes onto the first ice crystal as it falls.

Ice crystal: A tiny piece of ice. A snowflake starts as one and grows from one.

Hexagon: A shape with six sides. NOAA's snowflake simulator page says every snow crystal has a six-sided, hexagonal shape.

Temperature: How cold or warm the air is.

Humidity: How wet the air is.

Middle: The Fuller Science, in Plain Words

Snow is precipitation in the form of ice crystals.

That is how NOAA's NESDIS Ice and Snow page puts it.

Precipitation is water that falls from clouds.

It starts in a cold cloud

The NESDIS page says snow originates in clouds when temperatures are below the freezing point.

NOAA gives that freezing point as 0 degrees Celsius, or 32 degrees Fahrenheit.

On that page, water vapor in the atmosphere condenses directly into ice, without going through the liquid stage.

Once an ice crystal has formed, NOAA says it absorbs and freezes more water vapor from the air around it.

It grows into a snow crystal or a snow pellet. Then it falls to Earth.

Why six sides, and why the arms match

NOAA's story page says the ice crystals that make up snowflakes are symmetrical, or patterned.

NOAA says that is because they reflect the internal order of the crystal's water molecules.

The molecules arrange themselves in predetermined spaces. NOAA gives the name for that: crystallization.

That is how NOAA explains a six-sided snowflake.

NOAA's snowflake simulator page says the same shape in short form: every snow crystal has a six-sided, hexagonal shape, but they come in all different arrangements and sizes.

As the crystal falls, its six arms can branch off in new directions. The six-sided shape is still maintained.

NOAA says the arms look identical because each arm experiences the same atmospheric conditions.

Temperature first, humidity second

NOAA says it is ultimately the temperature at which a crystal forms that determines the basic shape of the ice crystal.

Humidity matters too, but NOAA says it matters to a lesser extent.

NOAA gives two examples, in NOAA's own figures:

Long needle-like crystals at 23 degrees F.

Very flat plate-like crystals at 5 degrees F.

The fuller shape of one arm depends on the conditions the whole crystal meets as it falls.

A crystal might begin to grow arms in one manner. Minutes or even seconds later, slight changes in temperature or humidity can cause it to grow in another way.

The simulator page adds that, as a snowflake forms, it can move to different parts of the cloud, and differences in temperature and humidity affect its shape.

Why no two are exactly alike — with NOAA's qualifier

NOAA's story page asks: “So, why are no two snowflakes exactly alike?”

Its answer is about the path. Individual snowflakes all follow slightly different paths from the sky to the ground.

So they encounter slightly different atmospheric conditions along the way.

NOAA's conclusion, in its own qualifier, is that they all tend to look unique.

NOAA says they can resemble everything from prisms and needles to the familiar lacy pattern.

Words to know — Middle

Water vapor: Water in the atmosphere in gas form as NOAA uses the term on these pages — it can condense directly into ice in a cold cloud, and it can freeze onto a crystal that is already there.

Ice crystal: The first tiny piece of ice a snowflake grows from, and also the pieces that build its six arms.

Hexagon: A six-sided shape. A hexagonal snow crystal has six sides.

Temperature: How cold or warm the air is. NOAA says the temperature at which a crystal forms determines its basic shape.

Humidity: The wetness of the air. NOAA says it affects the basic shape too, but to a lesser extent than temperature.

Crystallization: NOAA's word for water molecules arranging themselves in predetermined spaces inside the crystal.