Why No Two Snowflakes Look Alike
by Brooke Carlisle
Broadcast 12.6 & 12.11.2015

snowflakes falling on cedar branches

Photo by W. Carter, CC 2.0.



You know the old saying “no two snowflakes are alike”? Well, there may be more truth to that than you think. I am from Hillsboro, Oregon, where the snow falls in wet, indistinguishable clumps. When I moved to Montana, I immediately noticed a difference.

Here, when the conditions are right, you can pick out each of the six arms of individual snowflakes. They look like tiny versions of the paper crafts that school-kids make, perfectly formed and yet unique. This led me to question how snowflakes are formed, and why each snowflake is one of a kind.

One snowflake expert is physicist Dr. Ken Libbrecht at the California Institute of Technology in Pasadena. Known as “The Snowflake Man,” his research has taken him around the world. As he says, “different locations produce different shapes due to different climates.”

Snowflakes, like rain, begin with evaporation, the process of water molecules changing from liquid on earth’s surface, to gas in the atmosphere. When atmospheric temperatures reach 14 degrees Fahrenheit or lower, clouds are super-cooled and some water particles in them begin to freeze. These particles attach to heavier pollen or dust particles in the clouds which, with the help of gravity, pull the frozen water to earth and collect more water vapor. Because of the composition of water molecules, they begin to crystallize into flat, six-sided plates. Every snowflake begins this way, but after this point the variation in shape starts to take place.

As the six-sided crystals fall and collect moisture, they begin to form a distinct shape. Snowflake shape is influenced mainly by humidity and temperature. In low humidity areas, the snowflake will not develop past the original flat hexagonal plate. In very cold temperatures, around -22 degrees Fahrenheit, the plates will grow into a linear column. Ten degrees warmer and six beautifully-shaped branches form from the original hexagon structure, producing the classic snowflake. Warmer still and the tiny plates grow into long needle-like structures. And finally, between -5 and 0 degrees, the plates return to the classic shape.

lone snowflake in winter

Photo by Aaron Burden, public domain image.

So it makes sense that snowflakes vary in different climates, but why are two flakes that fall from the same cloud so different? The individuality happens because no two snowflakes take the exact same path through the sky. Even slight variations will affect them. Atmospheric temperature and pressure are not uniform. There are layers and pockets throughout the sky. If snowflakes fall through one of these pockets, something very interesting happens: they can change form. These flakes usually become capped cylinders, a columnar shape with two flat plates stuck on each end, similar to barbells at a gym.

When Dr. Libbrecht is not traveling around the cool climates in the north, he is creating his own snowflakes in a laboratory in California. He makes “designer snowflakes” with help from a machine that uses electric fields and temperature changes. Interestingly, “The Snowflake Man” has never made two identical snowflakes in his lab. Even when using the same parameters, the ice has slightly varied reactions, such as a split tip versus a single point.

Whether made naturally or in the lab, no two snowflakes are alike. We know that humidity and temperature affect flake formation, but there is still much to learn. So the next time you’re caught in a snowstorm, stop, look closely at all those snowflakes swirling down around you, and appreciate each snowflake’s unique journey.