2005-12-09 / Columnists

Drawing On Science


by Stephen Yaeger

It’s snow season again; time for those long-awaited snow storms and one or two blizzards to get our minds off the long-hot summer that just passed. Did you ever notice how much we complain about the weather? You get a hot day, around 90 degrees and the TV newscasters are out on the street asking everyone who walks by, “How do you feel about this heat?” or “Are you hot enough today?” or “Would you rather be on the beach?” What do those bowling balls expect their victims to say? “It’s just what I wanted?” “No I’m nice and cool in this 90 degree heat.” “No I’d rather be here on this hot street talking to you.” Wait until our first snow fall. Can you guess what these Einsteins will ask? Think about it.

OK, for those of you who couldn’t care less about snow turn the page now. The rest of you can continue reading, so sit back and enjoy.

A snowflake is, basically, a thin piece of ice formed from water vapor molecules. It occurs when the temperature in the upper atmosphere falls to 32o F (0 oC). This is the freezing point of water or the point when water changes phase from a liquid to a solid (or from a solid to a liquid…you know, melting). The molecules that make up the water vapor begin to solidify forming ice crystals, which trap air. The crystals that make up the snowflakes have many surfaces and these surfaces tend to reflect light in all directions. Our eyes perceive this light as white, so that snowflakes will always appear white to us. If you have ever seen glacial ice it appears blue. This is because the ice is so fully packed that there is virtually no air in the crystals. When impurities in the air are trapped in the formation of the crystals the snow will, of course, become discolored.

Snowflakes have the shape of a six-sided hexagonal crystal. But the type of crystal varies depending on where they are formed. The common hexagonal shape that we are familiar with is formed in high clouds in temperatures ranging from 25oF to 32oF. At middle cloud heights six-sided, flat crystals form at temperatures of 21oF to 25oF. Hollow column crystals form at temperatures of 21oF to 14oF, at 10o F to 14oF sector plates form and at 3oF to 10oF dendrites or lacy hexagonal shapes form.

Snow flakes that form under favorable conditions will be symmetrical. This is due to three factors: 1. The chemical bond between hydrogen and oxygen within the water molecule itself. 2. The attraction and repulsive forces between water molecules. 3. Hydrogen bonds (weak bonds between hydrogen and oxygen atoms of adjacent water molecules). These factors dictate that during crystallization, the water molecules must align themselves to maximize attractive forces and minimize repulsive forces. There is only one physical way to do this: a hexagonal shape of the snowflake. If temperatures are uneven or the formation of the snow flake is affected by dirt, the resulting plate may not be symmetrical.

To maintain the crystallization of the snowflake, temperatures must be at the freezing point both in the high atmosphere where they formed and on the ground. If the temperature is warmer near the ground the snowflakes will melt and it will rain instead. High winds and falling snow result in a snowstorm. Blizzard conditions occur when the winds reach a velocity of at least 35 mph. The blizzard does not have to be falling snow. It can be snow that is being lifted from the ground — snow that has fallen previously. Or it can be a combination of falling and ground snow. In any case the visibility must be ΒΌ mile or less and the conditions must last for at least three hours.

When rain falls during conditions where the ground temperature and the air just above the ground is below freezing, the water droplets will freeze into small ice pellets before they reach the ground. This results in sleet. Freezing rain occurs when the rain water does not freeze until it actually touches the ground.

So get ready for the winter ahead. It is predicted that it will be a very cold one. OK, so you skeptics say there’s no such thing as global warming — that’s another topic.

Questions/comments?

E-mail Steve: Drawingonscience@ aol.com

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