Winter has arrived, and most of us are more occupied with slogging through slush than appreciating the intricate detail and shape of a single snowflake. But the onslaught of snow raises an interesting question—how exactly do snowflakes form?
Snowflakes begin their existence in clouds, which are made of water vapour. As the temperature outdoors falls below freezing, the water in the clouds crystallizes, and falls from the sky as snow rather than rain.
Snowflake formation is a dynamic process. A snowflake is constantly having its structure changed by environmental conditions, making it extremely improbable that anyone would see two identical snowflakes.
Many snowflakes are highly symmetrical. Their symmetry reflects the internal order of their constituent water molecules. Water molecules in the solid state, such as in ice and snow, form weak bonds with one another. During crystallization, the water molecules align themselves in order to maximize attractive forces and minimize repulsive forces. These ordered arrangements are what produce the symmetrical hexagonal shape of the snowflake.
Various factors affect how a snowflake forms its particular shape. Temperature, air currents and humidity influence the shape and size of the snowflake. Dust particles influence the weight of the snowflake, and can also cause cracks and breaks in the crystal, making it easier to melt.
Snowflake shapes vary according to the height of the clouds in which they were formed. Six-sided hexagonal crystals are generally shaped in high clouds. Needles or flat six-sided crystals form in middle-height clouds. And a wide variety of six-sided shapes are formed in low clouds.
Colder temperatures create snowflakes with sharper tips and may also cause the branching of the snowflake’s arms. Warmer temperatures cause snowflakes to grow more slowly, producing smoother, less intricate shapes.
