That’s an old adage, quite common in weather lore when the unique nature of a snowflake is described, and I’m sure you’ve heard it at least once in your life. However, this rule of thumb is only right to a point: snowflakes can indeed look exactly alike, only differing in the abundance of certain isotopes or the number of water molecules, thus making them technically not identical. When I read this, my childhood notions regarding the magic that was snow melted like Frosty during spring thaw. Yet, despite this elimination of wonder, the science behind the fascinating patterns that make up the structures of snowflakes infused a strange beauty back into them.
One of the biggest proponents to the formation of a snowflake is clouds. There are high, middle, and low clouds, and each shapes its water vapor differently. High clouds normally produce “six-sided hexagonal crystals,” according to Anne Marie Helmenstine, PhD. In the middle clouds, flatter six-sided crystals and needles are made. Last are the lower clouds where random assortments of six-sided shapes are generated. Temperature affects these shapes by making them more or less detailed to the human eye. Naturally, it’s the higher temperatures that make the snowflakes harder to form, thus the shapes are smoother without as much structural design. In general, the temperatures also yield specific patterns of snowflakes. The warmer ends of freezing (25-32 degrees Fahrenheit) produce the flimsy hexagonal structures. When the temperatures cool down, the shapes progress from the weak hexagons to needles, then hollow columns, sector plates, and dendrites. The latter shape is the most detailed to observe, but we have to wait for temperatures as low as ten degrees Fahrenheit to begin seeing them.
When observing a snowflake, the aesthetic qualities of their structure strike the human eye quite dramatically. One of the reasons is because a snowflake, for the most part, is symmetrical. In general, this is a result of the water molecules arranging themselves in an order that suits them best when they are in a solid state as opposed to a liquid one. This arrangement is based off the hydrogen bonds between these molecules. In the process of making these bonds, the water molecules try to get rid of as many “repulsive forces” as possible, and make as many “attractive forces” in return, according to About.com. The delicate balance they create results in the shapes that were being formed in the water vapor.
Surprisingly enough, snowflakes are not just water vapor. They contain dirt particles too. As they form, dirt and dust particles make their way into the structure and become an integral part of the weight of the snowflake as well as provide it with durability, states Dr. Helmenstine. So, the next time you open your mouth to catch a snowflake on your tongue, think about that!