Earlier this week we had a snow forecast that could really have affected our operations here at COSI. I was watching the weather forecasts really closely to determine how much of the possible 10 inches of snow we could get here in Columbus and one of the forecasters mentioned the possibility of thundersnow. This is a term I've heard of before, even experienced but I really don't know a lot about it. So I turned to our resident science guy extraordinaire, Steve Whitt and asked him what in the world is thundersnow? How does it form and what is it?
Here's what I found out from Steve:
It all comes down to one idea: the world is made of atoms. Atoms in air combine together to form molecules, mostly nitrogen molecules (made of two nitrogen atoms) and oxygen molecules (made of two oxygen atoms). When these molecules are warm, they move quickly and bounce off one another. When they're cooler, they slow down and don't bounce as much.
In colder air, then, the molecules can get closer together while in warmer air they're further apart. The more molecules, the heavier the air, so cold air is heavier than warm air. When cold air and warm air meet, the cold air pushes under the warm air, sending the warm air higher.
Air isn't much good at absorbing heat from the Sun; instead, it gains heat from the ground. So when you push warm air up, it cools (think about the tops of mountains - it's cold up there!) As the warm air cools, water vapor turns to drops of liquid water, forming clouds. If the drops are big enough, they fall from the cloud as rain or (if the cold air below is cold enough) flakes of snow.
One more thing: all that moving air creates lots of static electricity. Think of rubbing a balloon on your head, or getting clothes from the dryer. That static buildup can result in a discharge - a spark - that also makes a sound. The spark we call lightning and the sound we call thunder.
Everything I've described so far applies to thunderstorms such as we often get in the spring and summer. There's so much heat energy available at these times that air masses can move all over the country, colliding, pushing on one another, and creating storms. In the winter, generally everything is pretty cold, so there's not much energy available to create big air movements. But every once in a while, there's enough energy available to create a powerful snowstorm that includes thunder and lightning.
One interesting fact, and another reason that thundersnow is so rare, is that the falling snow actually muffles the thunder. While thunder from a rainstorm can be heard many miles away, thunder generated in a snowstorm is often only audible up to two or three miles from the source. This means that even if you are near a rare thundersnow, you may never know it because the snow deadens the sound.
That is so cool! I love that when I have a science question I can ask the experts right here in the place that I work. Thanks, Steve, for enlightening me. I can't wait to bring this up next time I'm having dinner with friends!
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