How Snowflakes Form

Love it or hate it, snow is a major part of New England winters. To make matters more exciting, no two storms seem to be alike. This is partially because of the consistency of snow, which is determined by a series of atmospheric factors such as temperature, wind, dew point, humidity, etc. This creates a wide range of probabilities that can be tricky to predict. The formation of a snowflake is caused by a chemical reaction known as crystallization. Did you know that snowflakes are actually classified as minerals? How cool is that?

Close up of snow crystals forming. Photographer: Alexey Kljatov.

A snowflake begins its life as a particle, or a speck of dust. Traveling through the air, water vapor condenses (changing from a gas to a solid) on this particle. From here, two formations may occur. Colder and drier conditions will cause a faceted prism to form. Warmer and wetter conditions will cause branching patterns. All snowflakes are hexagonal in shape, with six sides aptly referred to as “six-fold symmetry.” This is because the crystallization process works on the molecular level, and frozen water molecules produce six sides. However, few snowflakes are perfectly symmetrical – the arms and sides grow independently of one another, so subtle differences in the branching patterns are typical.

Temperature and humidity play a role in which processes occur. Changes imperceptible to humans determine the growth pattern. Sometimes both processes occur at once. As the snowflake is blown around the cloud, it experiences many changes in temperature and humidity. The likelihood of a single particle undergoing exactly the same set of conditions as another particle is unlikely. This is why no two snowflakes are truly identical.

As a snowflake forms and gains mass, it eventually becomes too heavy to stay in the cloud and may even combine with other snow crystals to fall as clumps. As it journeys through the atmosphere, it will undergo additional changes. If temperatures increase as it approaches earth, it may change to water and fall as rain. If temperatures remain around freezing or below, it will reach the earth as a snowflake. Ground temperatures will then determine if it melts or begins to pile up with other snowflakes, forming and contributing to what is referred to as the snow pack.