Crystal Magic: The science of snowflakes

Ever look closely at a snowflake?

Fern-like stellar dendrite.

It's mostly true no two snowflakes precisely alike. There are actually many different varieties of snow crystals. The precise meteorological conditions during growth and travel of snowflakes through the atmosphere determines what type of snow crystal falls in your backyard, or on your nose.

Snow crystals at the Huttner Weather Lab. Paul Huttner/MPR News

What is a snowflake?

What we think of as snowflakes are really tiny snow crystals. I’ve interviewed North Dakota native and snow crystal expert Dr. Kenneth Libbrecht of Cal Tech about the science of snowflakes. Here’s a good description of what makes a snowflake from his amazing site

When people say snowflake, they often mean snow crystal. The latter is a single crystal of ice, within which the water molecules are all lined up in a precise hexagonal array. Snow crystals display that characteristic six-fold symmetry we are all familiar with.

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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The morphology of snow crystals

I believe the snowflake is as close to god as we can come on earth. The process of growing snow crystals in the atmosphere is simply magical.

Snow crystals grow from water vapor directly to ice in the atmosphere, skipping the liquid water phase. That’s pretty incredible if you think about it.

It turns out temperature and humidity in the zone where snowflakes form are critical to determining the type of snow crystal that develops. If temperatures are below zero, plates and columns form. At 5 degrees above zero, large beautiful stellar dendrites and hexagonal plates magically appear. This "Dendritic Growth Zone" (DGZ) produces large flakes that pile up in a hurry.

Stellar dendrite.

At temperatures around 20 degrees, a magical variety of prisms, columns and needles flutter earthward. Dendrites and plates are again favored as temperatures approach the freezing mark.

Cal Tech

So the next time beautiful snowflakes fall around you, take a moment to think about just how unique and magical each snow crystal really is.