Thunder Shakes the Northland

by Kevin Strauss

Some people talk about robins or butterflies or green grass as the harbingers of spring, but for me, it is thunder. Last week the sky turned gray and let loose with our first spring thunderstorm. The rain melted much of our winter snowpack and snowmobilers parked their sleds in the garage until next winter.

The “thunder” in thunderstorms is actually the sound produced from lightning strikes. When wind from thundercloud updrafts build up enough of an electrical charge in a cloud, a bolt of white-hot lightning seems to shoot from the sky to the ground. It is a little like a gigantic version of a person shuffling their feet across a shag capet to pick up a spark of static electricity. When the spark jumps from your finger to the oven door, or to your younger sister, it makes a soft “pop” imagine what could happen if your shoes on the carpet could build up a spark 1,000 times stronger. Then you’d have a lightning bolt. (Meteorologists tell us that actually an invisible lightning bolt from the clouds to the ground precedes the visible bolt, which actually travels from the ground to the clouds.)

This lightning is 2.5 times the temperature of the surface of the sun and the heat makes the air rapidly expand around the bolt. This rapid expansion makes the thunder that we hear. Of course, unless we are right at the sight of the lighting strike (never a good idea) we will almost always see a flash of lighting before we hear the booming thunder. That is because light moves faster than sound. For all practical purposes, the speed of light seems instantaneous on the earth’s surface, but sound only travels about 1,000 feet per second. That is why you can count the time between the flash of lightning and the sound of thunder, divide by five and estimate the distance to a thunderstorm (a mile is 5,280 feet).

Some people might argue that lightning doesn’t always cause thunder, citing the example of “heat lighting” or flashes from cloud to cloud in the summer sky that don’t result in thunder. These flashes do produce thunder, but it is so far away that by the time we hear the sound, we have often forgotten about the flash.

Lightning safety: When you hear thunder or see lighting, it is a good idea to get off any water (lake, river) and make sure that you are not the tallest thing in the area. Lighting seeks the easiest path between the sky and the ground. Don’t stand under a tree or lamp post if it is the tallest thing around since that is where lightning will often strike. It is also a good idea to turn off and unplug expensive electronic equipment during a thunderstorm. Surge protectors offer some protection, but a nearby lightning strike may still damage delicate equipment like computers.

The Ely Timberjay