Lightning is an electrical discharge and nature’s balancing mechanism for distributing charge throughout the atmosphere.
Thunderstorms become electrified when electrons, which are negatively charged particles, are shaved off one water particle — like a raindrop, snowflake or hailstone — and end up on another, leaving the former with a net positive charge and the latter a bit extra negative. Generally speaking, ice crystals acquire a positive charge, while raindrops take on a negative charge.
That makes the top of a cloud, where temperature are well below freezing, positively charged. Below that is a more expansive “central negative” within the storm. A shallow, broad positive charge sits at the storm’s base like the bottom of a hamburger bun.
Most lightning we see is either intracloud (within the cloud) or takes the form of cloud-to-ground bolts, most commonly originating from the middle negative charge. The greater the electrical field within a cloud, the more “sparky” the storm will be.
Getting an electric spark to jump through thin air is tricky. The ambient electric field has to be great enough to overwhelm the “dielectric breakdown strength” of air.
Think of a dam. It prevents water from flowing beyond it, unless the volume of water behind it reaches a threshold sufficient to burst the dam. Then the stored-up water can break through unimpeded.
For air, that magic number is 3 megavolts (or 3 million volts) per meter for dry air (it will change some in a storm). Charge accumulating on the surface will begin to bleed into thin air in a fine stream of electrons known as a “corona” discharge. That heats the adjacent air, lowering the resistance and making it possible for that spark to begin spreading in jagged increments.
It’s unclear what processes unfold within a cloud, but eventually what’s called a “stepped leader” of electricity races toward the ground, leaping in a branched, fractal pattern.
“Upward streamers,” or narrow tendrils of electricity, reach skyward from the surface, akin to a group of students raising their hands. Eventually, the downward stepped leader connects with one of the upward streamers to create an unbroken channel of electricity between the cloud and the ground. Current pulses surge through the channel, each causing a burst of light. That’s why lightning appears to flicker.
Surprising facts about lightning
- Lightning isn’t that thick. In fact, it’s only an inch or two across. It just looks wider because of luminosity.
- Lightning is five times hotter than the surface of the sun. Within that narrow lightning channel, the electricity heats the air to nearly 55,000 degrees. That causes a rapid expansion of the air, which produces the atmospheric shock wave we hear as thunder.
- Lightning can be triggered. Researchers at Los Alamos National Laboratory in New Mexico use rockets to trigger lightning, and then employ high-speed cameras and instruments to collect data. It’s also well-established that airplanes, helicopters, tall man-made structures and even wind turbines can spark their own strikes.
- “Upward lightning” is a thing. It’s exactly what it sounds like — lightning that leaps from the ground to the cloud, fanning outward along the cloud’s expansive lower positive charge. In fact, self-initiated upward leaders are common from man-made transmission/broadcast towers, and are an area of emerging research.
- Some lightning is more likely to spark wildfires. Although lightning is extremely hot, it is also brief. That limits its window of opportunity to ignite a wildfire. But instead of current flowing between the sky and ground in a brief series of staccato bursts, some lightning takes the form of a “continuing current” discharge. That means the current flows over longer-duration pulses. Because the current is heating the ground for longer, the odds of a wildfire climb markedly.
- Men are struck roughly four times as often as women. In the United States, men account for 84 percent of lightning fatalities, and women make up the remaining 16 percent.
- Lightning fatalities are trending downward. Because of improved forecasts, education and awareness, lightning fatalities have decreased significantly in recent decades. An average of 43 people died of lightning strikes annually in the United States between 1989 and 2018, but the average dropped to 23 between 2012 and 2022. A record low 11 deaths occurred in 2021.
Tips and facts to know for staying safe when there’s lightning
- Never shelter under a tree. If lightning strikes a tree, the charge can flow through the trunk and laterally strike individuals beneath it, or also spread through the ground. Many lightning tragedies have stemmed from individuals seeking shelter beneath trees. The previous lightning fatality in DC, which took place on May 17, 1991, occurred when a group sheltered beneath a tree during a lacrosse game.
- Leisure activities — especially fishing and boating — are the greatest sources of lightning fatalities. “[F]ishermen and boaters are likely to be out in the open and more vulnerable to a direct lightning strike,” a report from the National Lightning Safety Council from 2020 stated.
- Lightning can strike even in blizzards. Thundersnow is real and it can be dangerous. On Jan. 25, 1990, lightning hit a light pole during a thundersnow storm in Crystal Lake, Ill. The charge traveled through the frozen ground and injured 11 people nearby shoveling snow or pushing stranded motorists.
- Lightning can travel 10 or more miles away from a parent thunderstorm and even strike in clear air far from any rain. These “bolts from the blue” are often more powerful and potent, since they originate from the positively charged top of a thunderstorm. These are among the most dangerous, since they can strike in otherwise tranquil conditions. That’s why experts recommend sheltering at the first sign of thunder, as that’s a sign that you’re close enough to be struck by lightning.
- Ninety percent of lightning-strike victims survive. There are an average of 30 lightning fatalities in the United States every year. The lightning strike near the White House on Thursday brought this year’s fatality count to 11.
Read more about lightning …
‘Gigantic jet’ lightning is a mystery. These researchers are solving it.
Jonathan’s story: After tragic ‘bolt from the blue,’ two simple rules that could save your life
Bolts from the blue: Here’s how lightning can strike when a storm is tens of miles away
Where lightning hit the most in the US in 2021