A lightning strike or lightning bolt is a lightning event in which an electric discharge takes place between the atmosphere and the ground. Most originate in a cumulonimbus cloud and terminate on the ground, called cloud-to-ground (CG) lightning. A less common type of strike, ground-to-cloud (GC) lightning, is upward-propagating lightning initiated from a tall grounded object and reaching into the clouds. About 25% of all lightning events worldwide are strikes between the atmosphere and earth-bound objects. Most are intracloud (IC) lightning and cloud-to-cloud (CC), where discharges only occur high in the atmosphere. Lightning strikes the average commercial aircraft at least once a year, but modern engineering and design means this is rarely a problem. The movement of aircraft through clouds can even cause lightning strikes.
Lightning strikes can injure humans in several different ways:
Warning signs of an impending strike nearby can include a crackling sound, sensations of static electricity in the hair or skin, the pungent smell of ozone, or the appearance of a blue haze around persons or objects (St. Elmo's fire). People caught in such extreme situations â without having been able to flee to a safer, fully enclosed space â are advised to assume the "lightning position", which involves "sitting or crouching with knees and feet close together to create only one point of contact with the ground" (with the feet off the ground if sitting; if a standing position is needed, the feet must be touching).
Lightning strikes can produce severe injuries in humans, and are lethal in between 10 and 30% of cases, with up to 80% of survivors sustaining long-term injuries. These severe injuries are not usually caused by thermal burns, since the current is too brief to greatly heat up tissues; instead, nerves and muscles may be directly damaged by the high voltage producing holes in their cell membranes, a process called electroporation. Metallic objects in contact with the skin may "concentrate" the lightning's energy, given it is a better natural conductor and the preferred pathway, resulting in more serious injuries, such as burns from molten or evaporating metal. At least two cases have been reported where a strike victim wearing an iPod suffered more serious injuries as a result.
During a flash, though, the current flowing through the channel and around the body can generate large electromagnetic fields and EMPs, which may induce electrical transients (surges) within the nervous system or pacemaker of the heart, upsetting normal operations. This effect might explain cases where cardiac arrest or seizures followed a lightning strike that produced no external injuries. It may also point to the victim not being directly struck at all, but just being very close to the strike termination.
According to the CDC there are about 6,000 lightning strikes per minute, or more than 8 million strikes every day. As of 2008 there were about 240,000 "lightning strikes incidents" around the world each year.
According to the National Oceanic and Atmospheric Administration in 2012, over the twenty years to 2012 the United States averaged 51 annual lightning strike fatalities, making it the second-most frequent cause of weather-related death after floods. In the US, as of 1999, between 9 and 10% of those struck died, with an annual average of 25 deaths in the 2010s decade (16 in 2017).
In the United States in the period 2009 to 2018 an average of 27 lightning fatalities occurred per year. In the United States an average of 23 people died from lightning per year from 2012 to 2021. Some people suffer from lifelong brain injuries.
As of 2005, in Kisii, Kenya, some 30 people die each year from lightning strikes. Kisii's high rate of lightning fatalities occurs because of the frequency of thunderstorms and because many of the area's structures have metal roofs. As of 2013, direct-strike casualties could be much higher than reported numbers. In 2015 it was reported that between five and ten deaths from lightning occur in Australia every year with over 100 injuries occurring.
In 2018, it was reported that "a direct strike accounts for only 3 to 5 percent of all injuries and death, while ground currents, which spread out over the ground after lightning strikes, account for up to 50 per cent... ...Where the lightning strikes the ground, the ground becomes highly electrified and if you're within that area of ground electrification..." you can receive an electrical shock from the lightning.
In 2021, one report wrote that "30-60 people are struck by lightning each year in Britain, and on average, 3 (5-10%) of these strikes are fatal." It also estimated that "...one in four people struck by lightning were sheltering under trees."
Lightning strikes are a threat to animals. They are most studied as a threat to livestock used in human ranching and agriculture. In particular, large quadrupeds such as cattle, sheep, and horses are at particular risk to the electricity from a lightning strike. A few unlucky ones are struck directly by lightning or by side flashes, but there is a larger danger: step potential and step voltage. When a huge amount of electricity goes to ground, such as during a lightning strike, there can become a step voltage difference between multiple points of contact with the ground. This difference creates a path for the current to pass through an entity standing on the affected ground. Bipeds such as humans are less likely to fall victim to this, as their two feet are comparatively close together, reducing the voltage difference. If some current goes through them, it may be largely through non-lethal areas such as the legs. Quadrupeds are not so lucky. The large distance between their front legs and back legs invite the surging electricity to path through one set of legs, through their body, and out the other set of legs. Further, this electricity will go through critical organs in their heart and nervous system more easily than for humans, killing them. This can result in simultaneous mass kills of livestock that crowded near a tree from the current in the ground itself. This situation is worsened as trees provide shade from the heat and partial shelter from the rain, and thus attract livestock to congregate nearby. But trees also attract lightning strikes due to being a local high point.
Similarly, a metal or wire fence struck by lightning is also a danger. Livestock that don't seek shelter under trees are reported to sometimes gather at the periphery of a property as if trying to get away from a storm, which can result in groups of livestock all in contact with a fence. To mitigate these risks, farmers and ranchers using wire fences are encouraged to stick ground rods every so often along them. Otherwise, a lightning strike can easily travel down a fence and electrocute livestock touching any section of it. They are also encouraged to discourage livestock from lone trees on hilltops, which can attract both a herd of nervous livestock while being a prime danger area for lightning strikes in a storm. If deterrence with a wooden fence or the like is not feasible or desirable (such as for trees intended to provide such shade in hot climates), covering the surface near the at-risk tree with gravel or a similarly non-conductive insulating material is recommended. For even further protection, the tree can have metal wire wrapped around the trunk, connected with vertical wire that goes beneath the surface and spreads radially from the tree. This would attempt to provide a low-resistance path to guide the electric current farther away and deeper underground during a strike.
Deaths by lightning to large livestock don't leave obvious marks as to the cause to an untrained eye; afflicted cattle appear to have simply fallen over. This lack of obvious sign means that farmers sometimes incorrectly classify livestock death as due to lightning, or possibly dishonestly attempt to pass off deaths due to negligence as lightning deaths as a form of insurance fraud. One study of cattle deaths claimed to be the result of lightning in Belgium found that only around half of the deaths claimed to be due to lightning were verified by expert veterinary analysis. Still, making a conclusive determination of cause of death can be difficult even for forensic investigators who know what to look for.
The effect of lightning on wild animals is poorly documented and not closely tracked, but seem to be a risk to wild quadrupeds for similar reasons as livestock from the cases that are known. One mass mortality incident in Norway saw 323 wild reindeer killed by lightning.
In sparsely populated areas such as the Russian Far East and Siberia, lightning strikes are one of the major causes of forest fires. The smoke and mist expelled by a very large forest fire can cause secondary lightning strikes, starting additional fires many kilometers downwind.
When water in fractured rock is rapidly heated by a lightning strike, the resulting steam explosion can cause rock disintegration and shift boulders. It may be a significant factor in erosion of tropical and subtropical mountains that have never been glaciated. Evidence of lightning strikes includes erratic magnetic fields.
Telephones, modems, computers, and other electronic devices can be damaged by lightning, as harmful overcurrent can reach them through the phone jack, Ethernet cable, or electricity outlet.
Lightning currents have a very fast rise time, on the order of 40 kA per microsecond. Hence, although lightning is a form of direct current, conductors of such currents exhibit marked skin effect as with an alternating current, causing most of the currents to flow through the outer surface of the conductor.
Hundreds of devices, including lightning rods and charge transfer systems, are used to mitigate lightning damage and influence the path of a lightning flash.
A lightning rod (or lightning protector) is a metal strip or rod connected to earth through conductors and a grounding system, used to provide a preferred pathway to ground if lightning terminates on a structure. The class of these products is often called a "finial" or "air terminal". A lightning rod or "Franklin rod" in honor of its famous inventor, Benjamin Franklin, is simply a metal rod, and without being connected to the lightning protection system, as was sometimes the case in the past, will provide no added protection to a structure. Other names include "lightning conductor", "arrester", and "discharger"; however, over the years these names have been incorporated into other products or industries with a stake in lightning protection. Lightning arrester, for example, often refers to fused links that explode when a strike occurs to a high-voltage overhead power line to protect the more expensive transformers down the line by opening the circuit. In reality, it was an early form of a heavy duty surge-protection device. Modern arresters, constructed with metal oxides, are capable of safely shunting abnormally high voltage surges to ground while preventing normal system voltages from being shorted to ground.
The exact location of a lightning strike and when it will occur are still impossible to predict. However, products and systems have been designed of varying complexities to alert people as the probability of a strike increases above a set level determined by a risk assessment for the location's conditions and circumstances. One significant improvement has been in the area of detection of flashes through both ground- and satellite-based observation devices. The strikes and atmospheric flashes are not predicted, but the level of detail recorded by these technologies has vastly improved in the past 20 years.
Although commonly associated with thunderstorms at close range, lightning strikes can occur on a day that seems devoid of clouds. This occurrence is known as "a bolt from the blue [sky]".
Lightning interferes with amplitude modulation (AM) radio signals much more than frequency modulation (FM) signals, providing an easy way to gauge local lightning strike intensity.
The U.S. National Lightning Safety Institute advises American citizens to have a plan for their safety when a thunderstorm occurs and to commence it as soon as the first lightning is seen or thunder heard. This is important, as lightning can strike without rain actually falling and a storm being overhead, contrary to popular belief. If thunder can be heard at all, then a risk of lightning exists.
The National Lightning Safety Institute also recommends using the F-B (flash to boom) method to gauge distance to a lightning strike. The flash of a lightning strike and resulting thunder occur at roughly the same time. But light travels 300,000 km/sec, almost a million times the speed of sound. Sound travels at the slower speed of about 340 m/sec (depending on the temperature), so the flash of lightning is seen before thunder is heard. A method to determine the distance between lightning strike and viewer involves counting the seconds between the lightning flash and thunder. Then, dividing by three to determine the distance in kilometers, or by five for miles. Immediate precautions against lightning should be taken if the F-B time is 25 seconds or less, that is, if the lightning is closer than 8 km or 5 miles.
A 2014 report suggested that whether a person was standing up, squatting, or lying down when outside during a thunderstorm does not matter, because lightning can travel along the ground; this report suggested being inside a solid structure or vehicle was safest. The riskiest activities include fishing, boating, camping, and golf. A person injured by lightning does not carry an electrical charge, and can be safely handled to apply first aid before emergency services arrive. Lightning can affect the brainstem, which controls breathing.
Several studies conducted in South Asia and Africa suggest that the dangers of lightning are not taken sufficiently seriously there. A research team from the University of Colombo found that even in neighborhoods that had experienced deaths from lightning, no precautions were taken against future storms. An expert forum convened in 2007 to address how to raise awareness of lightning and improve lightning-protection standards, and expressed concern that many countries had no official standards for the installation of lightning rods.
Safety measures
Airplanes are commonly struck by lightning without damage, with the typical commercial aircraft hit at least once a year. Sometimes, though, the effects of a strike are serious.
A 2017 lightning bolt across the midwestern United States set the record for the longest lightning bolt ever detected. The bolt stretched for 515 miles from Dallas, Texas to Kansas City, Missouri. The World Meteorological Organization confirmed its record-breaking status in July 2025.