Snow is an all-too-familiar feature of the colder months across much of the U.S., but how much do you know about the science of snowflakes?

There will be plenty of snowflakes falling on Wednesday with a major Nor’easter expected to bring heavy snow.

"A snowflake begins to form when an extremely cold water droplet freezes onto a pollen or dust particle in the sky," explains NOAA on its website. "This creates an ice crystal. As the ice crystal falls to the ground, water vapor freezes onto the primary crystal, building new crystals – the six arms of the snowflake."

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NOAA notes that the ice crystals that comprise snowflakes are symmetrical because they reflect the order of the crystal’s water molecules as they arrange themselves in predetermined spaces, a process known as crystallization. This forms a six-sided snowflake, the scientists explain.

"Ultimately, it is the temperature at which a crystal forms — and to a lesser extent the humidity of the air — that determines the basic shape of the ice crystal," NOAA says. "Thus, we see long needle-like crystals at 23 degrees F and very flat plate-like crystals at 5 degrees F." 

"The intricate shape of a single arm of the snowflake is determined by the atmospheric conditions experienced by entire ice crystal as it falls," NOAA adds. "A crystal might begin to grow arms in one manner, and then minutes or even seconds later, slight changes in the surrounding temperature or humidity causes the crystal to grow in another way." 

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The journey to the ground is also responsible for the uniqueness of each snowflake, according to NOAA. "Individual snowflakes all follow slightly different paths from the sky to the ground —and thus encounter slightly different atmospheric conditions along the way," it says. "Therefore, they all tend to look unique, resembling everything from prisms and needles to the familiar lacy pattern." 

The terms snowflake and snow crystal have become interchangeable.

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"When people say snowflake, they often mean snow crystal," writes Kenneth Libbrecht, a physics professor at CalTech and author of "The Snowflake: Winter’s Frozen Artistry" on his website snowcrystals.com. "A snowflake, on the other hand, is a more general term. It can mean an individual snow crystal, but it can also mean just about anything that falls from the winter clouds. Often hundreds or even thousands of snow crystals collide and stick together in mid-air as they fall, forming flimsy puff-balls we call snowflakes. Calling a snow crystal a snowflake is fine, like calling a tulip a flower."

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