“Thunder only happens when it’s raining
Players only love you when they’re playing
Say women they will come and they will go
When the rain washes you clean, you’ll know, you’ll know”
– Fleetwood Mac, “Dreams”
Contrary to Fleetwood Mac’s claims, thunder does NOT only happen when it’s raining.
Thunder is the sound caused by lightning. Lightning is an electrostatic discharge, or a sudden flow of electricity between two electrically charged objects. This can happen between a cloud and the ground, two clouds, or even within different regions of the same cloud.
Lightning heats the air around it as hot at 30,000 degrees Celsius (54,000 degrees Fahrenheit). As the temperature of the air rockets upwards, so does the pressure. The heated air then expands outwards and compresses the surrounding air, forming a shock wave, creating the initial sharp “crack” of thunder. The disturbance in the surrounding air spreads out from the lightning strike, causing the thunder sound waves to travel farther and “rumble.”
In traditional thunderstorms– that is, rain with lightning and thunder- warm, moist air rises upwards, forming an updraft. The water condenses as the air rises, forming clouds. The clouds grow as more warm air rises, adding more water to the clouds and causing the water droplets to grow larger. The water droplets then become too heavy to be held up by the rising air, and they fall downward. Cool, dry air sinks through the cloud, creating a downdraft and pulling the water down as rain. The moving air and water creates electrically charged areas, sparking lightning.
Now let’s look into how we can get lightning and thunder without rain.
Take, for example, dry thunderstorms in the western states. Dry thunderstorms form from a combination of dry air and moist air. Farther up in the atmosphere, moist air creates a thunderstorm. As the rain falls to the ground, it encounters dry air. The dry air evaporates the rain before it can hit the ground. Thus, it’s a dry thunderstorm.
You can also have “rainless” thunder through thundersnow, a snowstorm accompanied by lightning and thunder. Thundersnow is pretty rare- one study estimated that only 0.07% of snowfalls in the United States came with lightning and thunder. There are three main ways thundersnow forms. The first is similar to how regular thunderstorms form. Warmer, moist air near the ground rises to mix with the colder and denser air higher in the atmosphere. The mixing causes disturbance, which then brings lightning and thunder. For thundersnow, the air has to be just the right temperature- warm enough to rise, but cool enough to prevent the snow from melting. The second way to make thundersnow is through pressure variations in a strong snowstorm. Air is pushed upwards, caused instability, which leads to lightning and thunder. The last way to form thundersnow is related to how lake effect snow forms. In the Great Lakes region, cold air can pass over the lakes, which hold relatively warm water. The warmer lake water warms the lower layer of air, which also picks up water vapor from the lake. As the water vapor rises, it cools to form snow, which then falls to the ground as the air mixes to create lightning and thunder.
Finally, there’s volcanic thunder. When a volcano erupts, ash, rock fragments, dust, and other particles are thrown into the air. These particles collide, generating static electricity, then lightning and thunder.
Thus, if thunder comes from lightning, and lightning does not only come with rain, then thunder does not always happen with it’s raining. If Fleetwood Mac wanted to be more accurate, they could sing, “Thunder only happens when there’s lightning.” Though maybe that’s a bit more awkward to sing.
Keep calm and science on.
Science On 