Saturday, July 6th 2013

Snow 101

Written by Amy Mayhew
Tuesday, December 28 2010

It’s December, and we Michiganders take snow for granted, don’t we? Yep, we’re content to dust off the shovel or fire up the snow blower without giving it a second thought.  But have you ever stopped and thought about how Mother Nature manufactures the stuff, or how she is able to make each flake completely unique?

How does snow form?

Snow forms when water vapor in the air drops below the freezing point. The vapor loses an amount of energy called the “heat of crystallization.” A similar process occurs to form ice, but the water is a solid, not a vapor.

Water vapor crystallizes the easiest on a particle of some sort – like a particle of dust, for instance. Once the process is underway, it explodes into action. Water vapor in the air easily crystallizes on existing water crystals.

If you look closely, you’ll find that each snowflake is based on a hexagonal shape. Even so, depending on temperature and humidity, the bonding can really result in any number of shapes. Throw weather conditions into the mix as the flake gets tossed around inside of a cloud, and one shape can quickly turn into another.

Are all flakes unique?
Pao-Kuan Wang, an atmospheric physicist who studies snowflakes at the University of Wisconsin-Madison says it all depends on how hard you look. Wang said that on the molecular level, they certainly appear to be different, but with the naked eye, they all sort of look the same.

Wang thinks the belief that all snowflakes look different came about “as a kind of appreciation for their complicated design, and because they look so beautiful.”

How big can snowflakes get?
OK – so there isn’t an official answer on this one, but what we do know is that a single snowflake is made up of many smaller snow crystals. In most cases, snowflakes measure less than 1/2- inch in diameter.  If conditions are just right – that is, near-freezing conditions, light wind and unstable atmospheric conditions, then you might see larger and irregular flakes forming, sometimes measuring nearly two inches in diameter.

Why is snow white?
Most natural materials absorb some sunlight which gives them their color. Snow, however, reflects most of the sunlight. The complex structure of snow crystals results in countless tiny surfaces from which visible light is efficiently reflected. What little sunlight is absorbed by the snow is absorbed uniformly over the wavelengths of visible light, thereby making snow white.

Is it ever too cold to snow?
We wish! No, it’s never too cold to snow. As long as there is some source of moisture and a way to lift or cool the air, it can snow at excruciatingly cold temps. It is true, however, that our heavier snowfall will happen when the temperatures near the ground are relatively warm – say 15 degrees Fahrenheit or warmer.

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