Stoke the fire for a forecast

Years ago, almost every household had a woodstove. Today we have electric fireplaces to set the mood and gas fireplaces that we can turn on with a switch. Times have changed, but people do still have wood-burning stoves. If you have one, you’ve probably noticed that some days very few sparks fly when you open the door to stoke the fire but other days, sparks fill the air. Well, you guessed it, Grandma had a theory; she believed it was a sign of incoming rain.

When I started to study meteorology and the physics of the atmosphere, I couldn’t wait to find out why this was. Well, as is so often the case with many of Grandma’s sayings, there is some pretty solid science behind it.

Air is a mixture of gases, largely composed of nitrogen and oxygen. Air is generally considered an insulator and would be an excellent one if all the oxygen and nitrogen molecules were in a neutral state. However, the air is actually composed of varying quantities of neutral molecules and positive and negative ions. As the number of ions in the air increases, the air progressively becomes a better conductor. So where do these ions come from? Precipitation. High in the upper atmosphere, you’ll find large, less mobile ions. Falling rain, snow or even ice ahead of a weather system tend to pull these ions down toward the Earth, making the air a better conductor.

So, “when sparks begin to fly, a storm is nearby.”