Snow Crystals

Just as no two human fingers have identical prints, it is reported that no two snowflakes are the same. Perhaps no two snow crystals identical, but like fingers, many show similar characteristics.

Falling snow particles are classified into ten categories, according to shape. To classify falling snow crystals may sound like a scientific make-work project, but there is some reason for this apparent folly just as there is reason why snow crystals come in different shapes.

The basic hexagonal (six-sided) shape of all snow crystals derives from the shape and bonding of water molecules. Beyond that fundamental constraint, it boils down to a matter of micro-climate, the climate the snow crystal finds itself in as it grows. The two key factors in the micro-climate are temperature and humidity.

If the air is extremely wet and just a few degrees below freezing, only needles and columnar snow crystals form. Six-sided plate crystals grow if the temperature is somewhat colder (plus 10°F, minus 15°C). At plus 5°F (-15°C) star-like crystals grow. The more saturated is the air the more lacy and dendritic they are.

Even for a snowflake, there is no peace and stability in this world of ours. As the crystal grows it moves through the air within an ever-changing micro-climate that dictates a changing growth pattern. A crystal that started out to be a column may fall into cooler air that creates plate-like growth, so then it becomes a capped column. In extremely wet air, lumpy masses called graupel, ice pellets or hail develop. Evidently, the growth is so fast that the molecular forces trying to create beauty in the form of plates, stellar crystals, and columns cannot control the growth pattern.