Snow science 101: See how a snowflake forms and why each one is unique

A winter storm is settling in over the U.S. and soon snowflakes will be falling across the nation. Have you ever wondered how one forms?

Snow is made up of tiny ice crystals that can transform into a variety of intricate symmetrical patterns forming a beautiful snowflake. And because every snowflake travels a different path from the sky to the ground, each one is unique.

Here’s a closer look at the science of snow:

The birth of a snowflake

The diagram below, inspired by Japanese physicist Ukichiro Nakaya, illustrates how atmospheric temperature and humidity impact the growth of ice crystals as they start the process of becoming snowflakes. Once a snow crystal becomes a prism, it can head in one of two directions: plate or column.

From ice crystal to snowflake

First, a frigid droplet of water freezes onto a particle of dust or pollen in the sky, according to the National Oceanic and Atmospheric Administration. An ice crystal forms and water vapor freezes onto the original ice crystal as it drifts toward the ground, creating additional crystals and eventually a six-armed snowflake.

Each snowflake travels a slightly different path as it descends, and each can come in contact with varying atmospheric conditions on its route. As it falls, each snowflake will develops a unique appearance, which can resemble a simple prism or a lacy pattern.

How many snowflakes fall each winter? The number of snow crystals that fall from the sky each winter tallys to an estimated 1 septillion (that's 1,000,000,000,000,000,000,000,000 – or about a trillion trillion), according to the Library of Congress.

That's a lot of very unique snowflakes!

See how much snow has fallen near you!