Verifying 7 claims about lightning and thunder

Thunderstorms are most common during the spring and summer months, which means there is no better time to learn about lightning safety.

Many of us picked up lightning safety tips from family and friends over the years, but some of those words of wisdom are actually myths. The VERIFY team took reader questions about lightning and thunder to the experts to help you figure out what advice is worth listening to and what you can dismiss as urban legend.

THE SOURCES

• Chita Craft, meteorologist at KHOU in Houston
• Dave Downey, meteorologist at WOI in Des Moines, Iowa
• University Corporation for Atmospheric Research (UCAR)
• National Oceanic and Atmospheric Administration (NOAA)
• National Weather Service
• Insurance Information Institute
• Lightning Protection Institute
• Centers for Disease Control and Prevention (CDC)
• New York State Department of Health
• La Plata Electric Association

WHAT WE FOUND

1. Does lightning always strike the highest point?

No, lightning doesn’t always strike the highest point.

Although it’s true that lightning typically strikes tall objects, that’s not the case all the time and there’s some unpredictability to where strikes actually occur. That’s why it’s always dangerous to be outside during a thunderstorm no matter where you are.

“Lightning can strike the ground in an open field even if the tree line is close by,” NOAA says. “It all depends on where the charges accumulate.”

These charges that NOAA refers to are what creates lightning in the first place.

For lightning to form, the University Corporation for Atmospheric Research (UCAR), National Oceanic and Atmospheric Administration (NOAA) and the Canadian government explain ice and other water particles within a storm cloud must crash into each other to create opposite electric charges. This leaves negative charges near the bottom of the cloud.

The ground has positive charges, and opposites attract. So once enough negative charges build up, they begin to head toward the positive charges on the ground. Those charges, most of the time, build up at the highest point because they’re getting pulled by the opposite charge from the cloud. The charges meet not too far above the ground, creating lightning when they do. 

When lightning strikes a building or structure, it will then run along conductors — like metal or water — or electric currents until it reaches the ground. This is why metal lightning rods, when paired with metal cabling that connect to a ground network, are able to provide lightning protection to homes.

“Lightning rods (and the accompanying protection system) are designed to protect a house or building from a direct lightning strike and, in particular, a lightning-initiated fire,” the National Weather Service says. “Note that lightning protection systems do not prevent lightning from striking the structure, but rather intercept a lightning strike, provide a conductive path for the harmful electrical discharge to follow (the appropriate UL-listed copper or aluminum cable), and disperse the energy safely into the ground (grounding network).”

Once meeting the ground, the lightning equalizes the charges until the process starts over and the opposite charges begin building up again.

2. Can lightning strike the inside of your home if you leave a window open?

Yes, lightning can strike the inside of your home if you leave a window open. While it’s not likely lightning will strike you through an open window, your odds of being struck are higher with open windows than closed windows.

“Open windows do not increase the chance of lightning striking a house; however, leaving them open does allow lightning to more easily strike an object inside the house,” said WOI meteorologist Dave Downey.

“You should stay at least a few feet away from windows and doors whenever a thunderstorm is approaching,” Downey continued. “You're probably a little better off with windows closed, but the take home point is that it’s much more important to put at least a few feet of air between you and the window… You don’t want to be injured by shattering glass if lightning does happen to hit your window. You also don’t want to get your house wet by giving sheets of rain easy access indoors!”

3. Should you avoid taking a bath or shower during a thunderstorm?

Yes, you should avoid taking a bath or shower when lightning is in the area. Metal and water both conduct electricity, which makes the bathtub one of the riskier areas of the home.

“While a house is the safest place you can be during a storm, just going inside isn’t enough,” the Insurance Information Institute says. “You must avoid any conducting path leading outside, such as electrical appliances, wires, TV cables, plumbing, metal doors or metal window frames.”

According to KHOU meteorologist Chita Craft, there are 10 to 20 reported cases of people being electrocuted by lightning in their bathtubs every year.

Because metal and water conduct electricity, lightning can travel through pipes and jump to a person. Craft says this danger isn’t limited to the bathtub — it’s anything with metal piping, such as the toilet.

“So you don't want to be around any of that,” Craft said. “It's a good idea to avoid any water, any plumbing around the area and of course anything that could hold a charge.”

The Centers for Disease Control and Prevention (CDC) notes that the risk of lightning traveling through plastic pipes might be less than through metal pipes, but maintains it’s best to avoid any contact with plumbing and running water during a thunderstorm, even in a home with plastic piping.

4. Is it true each second between lightning and thunder means the storm is one mile away?

No, it’s not true that each second between lightning and thunder means the storm is one mile away. Actually, every five seconds is about a mile of distance.

Thunder is the sound created by a flash of lightning. Lightning heats the air it passes through, causing the air to expand. The air then cools quickly after the flash and contracts just as quickly as a result. The rapid expansion and contraction creates a sound wave: thunder.

The National Weather Service says that the sound of thunder takes about five seconds to travel a mile, while we see lightning the moment it strikes, regardless of distance. That means a lightning strike is one mile away for every five seconds it takes for thunder to follow. So if it takes 10 seconds between the lightning flash and the rumble of thunder, then the strike is two miles away; if it takes 15 seconds before there’s a thunderclap, then it’s three miles away, and so on. Typically, thunder can only be heard within 10 miles of a lightning strike, the National Weather Service says, so it’s unlikely the sound of thunder will travel for more than 50 seconds after lightning strikes.

Counting the difference in time between lightning and thunder isn’t the only way to judge a storm’s distance, the National Weather Service says. The actual sound the thunder makes is also a good way to estimate distance.

“Typically, a sharp crack or click will indicate that the lightning channel passed nearby,” the National Weather Service says. “If the thunder sounds more like a rumble, the lightning was at least several miles away.”

“Really, the point with that is that if you can hear the thunder, you're in the striking distance of the storm, no doubt,” Dave Downey said. “We've seen lightning strikes happen 15, 20 miles plus away from where the core of the thunderstorm is occurring.”

5. Is it true your car will protect you from lightning strikes?

You’ve probably heard that a car is the safest place to be if you’re caught outside during a storm because of its tires. The first part is true — if you can’t go inside a building during a storm, a car is the next safest structure — but it’s not because of a car’s rubber tires.

Most cars will protect you from lightning strikes because of their metal frame, which conducts lightning away from the car’s interior. The National Weather Service, Insurance Information Institute and Lighting Protection Institute all say the belief that a car’s rubber tires will protect you is a myth.

“Most cars are reasonably safe from lightning, but it’s the metal roof and metal sides that protect you, not the rubber tires,” the Lightning Protection Institute says. “Thus convertibles, motorcycles, bikes, open-shelled outdoor recreation vehicles, and cars with plastic or fiberglass shells offer no lightning protection.”

Chita Craft says this is because a car acts as a kind of “Faraday cage.” Basically, when lightning strikes a metal cage or container, it wraps around the exterior of the cage without traveling inside of it. So the outside gets struck by lightning, but the inside remains protected, so long as the car is completely enclosed.

The National Weather Service warns against leaning on car doors during a thunderstorm. That would allow any lightning that may run down the metal of the door to jump from the car to you. 

Dave Downey notes that lightning can total a car, even if the vehicle protects the person inside. He said a lightning strike can damage the car’s antenna, frame or even the electrical system.

“Being in a car, you're less likely to get hurt,” Downey said. “But that doesn't mean your car is going to survive without getting any damage.”

6. Is it safe to be on a phone during a thunderstorm?

As long as it’s a wireless phone, like most phones today, it’s fine. Corded phones, however, are dangerous.

“Avoid using landlines, except in an emergency,” the New York State Department of Health warns. “If lightning hits the telephone lines, it could flow to the phone. Cell or cordless phones, not connected to the building’s wiring, are safe to use.”

Dave Downey said cell phones are actually a good way to receive information about a storm. That’s because they don’t need to be connected to any wiring to work, unlike a desktop computer, for example.

The La Plata Electric Association in Colorado says lightning can travel through the electrical, phone, plumbing and radio/television reception systems once inside a home.

“Lightning always seeks the ground, so if it should happen to strike a building with electricity or plumbing, the current will typically travel through the electrical or telephone wiring or plumbing and then into the ground,” the La Plata Electric Association said. “This is the reason to avoid connection with running water (in showers, sinks, hot tubs) and electronic equipment (a corded telephone or computer).”

7. Does metal attract lightning?

No, contrary to popular belief, metal doesn’t attract lightning. That means lightning isn’t more likely to strike you because you’re wearing small metal objects such as glasses, piercings, watches, cell phones and jewelry.

“Height, pointy shape, and isolation are the dominant factors controlling where a lightning bolt will strike. The presence of metal makes absolutely no difference on where lightning strikes. Mountains are made of stone but get struck by lightning many times a year,” the National Weather Service says. “While metal does not attract lightning, it does conduct it, so stay away from metal fences, railing, bleachers, etc.”

It’s always a bad idea to stay outside during a thunderstorm, but it’s an even worse idea to stay outside and stand near a metal object. If lightning strikes the object, it could travel down the object until it can jump to you.

The difference with metal on your person is that lightning would have to strike you before whatever you’re wearing can conduct it.

Obviously, this doesn’t mean it’s safe to wave an umbrella, golf club or fishing pole high above your head in a thunderstorm. That creates a tall, pointy spot for lightning to strike.

“Your chances of a direct hit are higher when you are carrying a conductor above shoulder level. Be sure to avoid other metal objects as well, such as wire fences. You are more likely to be burned if you are in contact with metal when you are struck by lightning, the CDC says.”

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