Precipitation comes in many forms such as rain, sleet, hail and snow. A snowflake starts out as a dust particle. Then water vapor starts to condense onto the dust particle and if the temperature is cold enough it freezes. Most naturally occurring ice is shaped in a hexagonal structure. The snowflake becomes more and more formed because water molecules have an attraction for each other and water is more stable in the form of ice. The water molecule is even more stable in the form of ice when arranged in hexagonal layers, and that gives the snowflake a 6-sided symmetry. As more and more water vapor condenses onto this ice crystal, the snowflake grows.
Several factors influence the shape of any one snowflake, the temperature, humidity and the air currents. If there are a lot of dust and dirt particles mixed in during this freezing process, the shape of the snowflake is affected. As these ice crystals move up and down in the cloud with the updrafts and downdrafts they continue to form and be shaped. Finally the snowflake is heavy enough to escape the clouds updrafts and falls to the ground.
Falling to the ground can also alter its shape. If the snowflake spins it will probably keep its symmetrical shape. If they aren’t spinning when they hit the ground they will lose their shape and be lumpy.
Common snowflake shapes
The shape of the ice crystals that form the snowflake is dependent on temperature. Here is a list of their shapes and the temperature that they formed in.
25 – 32 F: Thin 6-sided hexagonal crystals, formed in the high clouds.
21 – 25 F: Needles or flat-sided crystals are formed in the middle height clouds.
14 – 21 F: Hollow columns
10 – 14 F: Sector plates, which are hexagons with indentations.
3 – 10 F: Dendrites, lacy hexagonal shapes.
Snowflakes are composed of many ice crystals that affect their shapes. They might start out as a one shape and land as another shape. You will probably never see two snowflakes that look alike, it is a constant though that in the formation of one, it is always 6-sided, or hexagonal.
Why is snow white?
Water is clear, so why is snow white. The answer has to do with the fact that snowflakes have so many light-reflecting surfaces that they scatter the light into all of its colors, so snow appears white. It has to do with how the brain perceives the light into the color.
Another form of snow
There is another form of snow that some people have never heard of or seen, it is called graupel, also referred to as snow pellets. Some describe it as soft fuzzy hail. It starts out as a snowflake and then combine with supercooled water droplets frozen together. These are small pellets, not large like hail might be and soft.
A side note about updrafts and downdrafts
A snowflake can go up and down in a cloud gathering more crystals that form its shape until it gets heavy enough to fall to the ground. You can actually see this updraft and downdraft action yourself when it hails. The next time it hails and if the hail is big enough, look for ones that have broken in half on the ground. You can see rings inside the hailstone. Each ring represents a trip up and down in the cloud. The hailstone rises and gathers another layer of ice, then it falls in the downdraft and melts a little bit, rises up again and refreezes picking up another layer of ice until it gets heavy enough to fall to earth.
Sam Montana © 05 January 2009
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