The science of snowflakes

Friday’s snow globe reminds us of the beauty and magic of snowflakes.

It is said no two snowflakes are alike. And it’s true there are many different types of snow crystals. But what atmospheric factors determine the type of snowflake that falls to earth?

Temperature-critical

Snowflakes form in the so-called “dendritic growth zone” (DGZ) a few thousand feet above us. It turns out the temperature in that layer at the time of snowflake formation is critical to determining what type of snow crystal falls to earth.

DGZ temperatures between 25 and 30 degrees produce hexagonal plates or big fat stellar dendrites like many of us saw today.

DGZ temperatures either side of 20 degrees may produce ice needles, columns, or prisms. Different types of dendrites and plates reappear with single-digit temperatures. Subzero temperatures magically produce more plates and columns.

What happens below the dendritic growth zone also impacts the type of crystals that ultimately land on your nose.

If temperatures are near the melting point during the trip to earth, the edges of snowflakes may bond and create big lumpy ‘stellar dendrite clusters.’ (Sounds like a good name for a new cereal if you’re listening, General Mills.)

One of the premier researchers on snow crystals is North Dakota native and Cal Tech physics professor Dr. Kenneth Libbrecht. I interviewed Ken about the science of snowflakes.

Ken was fascinated by snowflakes as a child in North Dakota. That fascination drove him to grow amazing snow crystals in his sub-freezing laboratory at Cal Tech.

His website snowcrystals.com is a beautiful and amazing resource on the physics of snowflakes.

So the next time you see snowflakes drifting to earth, think about what is happening in the dendritic growth zone a few thousand feet above you. The combination of temperature and pressure in that layer determines which kind of snowflakes land on your tongue.