Sometimes we hear thunder, but don’t see any lightning. Why?

Question Answered by Andrew McKaughan, Lead Meteorologist, National Weather Service-Pocatello Office

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There could be a number of reasons for this but first let’s start with what lightning and thunder are exactly. Lightning is created from the discharge of electric particles in the atmosphere and on the ground. As a thunderstorm moves it gathers positively charged particles along the ground that travel with the storm. As the differences in charges continue to increase, positively charged particles rise up taller objects such as trees, houses and telephone poles. A channel of negative charge, called a “stepped leader” will descend from the bottom of the storm toward the ground. This is all invisible to the human eye, and shoots to the ground in a series of rapid steps, all occurring in less time than it takes to blink your eye. As the negative leader approaches the ground, positive charges collect in the ground and surrounding objects. These positive charges “reach” out to the approaching negative charge with its own channel called a “streamer.” When these channels connect, the resulting electrical transfer is what we see as lightning. After the initial lightning strike, if enough charge is leftover, additional strokes of lightning will use the same channel and will give the bolt its flickering appearance.

On average, a lightning bolt strikes the Earth 100 times per second! This amounts to around 8 million lightning strikes per day or over 3 billion per year! The heat generated from a bolt of lightning can have a temperature of over 50,000 degrees, a temperature that’s over 5 times hotter than the surface of the sun! When a lightning strike occurs, the air around it expands rapidly and this rapid expansion causes millions of shockwaves, or sonic booms, that propagate outward away from the lightning bolt. All of this happens in just a fraction of a second and the sound created from these shockwaves are what we hear as thunder!

Under most circumstances, thunder can generally be heard within about a 10 mile range of the actual lightning strike, but certain atmospheric conditions can make this distance shorter or longer by a few miles.

Left: How sound waves travel through cool and warm air | Right: How warm and cool air affect the sound of thunder

All this being said, why do we not always see that lightning that causes thunder? The most likely reason is that the lightning strike that created the thunder you heard did not actually hit the ground. In addition to striking the ground millions of times per day, lightning strikes also occur within the clouds themselves and this also produces thunder! These lightning bolts are sometimes not as visible as the ones that reach the ground since they are occurring thousands of feet above the surface. The soundwaves from these bolts are still able to reach the ground sometimes however and will be heard as thunder. Other reasons could be because the lightning strike was obscured by a nearby mountain or building. Cloud-to-ground lightning strikes from far away could also be difficult to see due to low visibility from the rain that is falling in the area. Hope this answers your question and be sure to always go inside immediately when you see lightning or hear rumbles of thunder! When thunder roars, go indoors!

Static Electricity
Static electricity is the build-up of an electrical change on the surface of an object. The reason it’s called static electricity is because the charges stay in one area for a time and don’t flow or move to another area.

Atoms are made up of protons, neutrons and electrons. The electrons move on the outside of the atom. A static charge happens when two surface touch each other and the electrons move from one to the other. One of the objects will have a positive charge and the other a negative charge.

If you rub an object like a balloon quickly with a piece of cloth, the changes build up. Lightning is essentially a giant static electricity shock.

What you will need: a piece of cloth, 2 Styrofoam plates

  1. Rub the base of a plate with the cloth.
  2. Place the plate on a flat surface.
  3. Try to place the other plate (base-down) on the other plate and watch as they repel.

This trick works due to static electricity. When you rub the plate with the cloth, the plate gains electrons from the cloth and becomes negatively charged. These electrons repel the electrons in the other plate.

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