People and Community Science and Technology

What to know if lightning strikes

UM weather expert and senior research associate Brian McNoldy explains the science behind lightning and how to stay out of its path.
Lightning over Miami.

With thunderstorms interrupting our afternoons almost daily at this time of year, it is important to remember how to stay safe from lightning.

Brian McNoldyUniversity of Miami senior research associate Brian McNoldy, a tropical cyclone specialist at the Rosenstiel School of Marine and Atmospheric Science, shares some insights as to what causes lightning and how to protect yourself from it.

Why does Florida attract so much lightning?

Florida gets a lot of thunderstorms just because of its warm and humid tropical climate, and because it's surrounded by water. During the rainy season (mid-May through mid-October), a sea breeze sets up almost daily. A sea breeze is a boundary between the air over land and the air over the water that migrates during the day as the land heats up. When the atmosphere becomes unstable — due to heating from the sun for example — that boundary becomes the focus for thunderstorm development.

Thunderstorms often move slowly here because of a lack of strong steering winds, so a particular location might get torrential rain and frequent lightning for quite some time. A map of climatological lightning activity reveals that in the United States, Florida is a hot spot for lightning activity, but other areas of the world get even more (near central Africa, such as in the Democratic Republic of Congo, as well as in northern Colombia, Paraguay and northeastern Argentina in South America, and Kuala Lumpur and Indonesia in Asia). However, all of the areas with really high values are warm and humid most of the year.

Florida averages about 3,500 cloud-to-ground lightning flashes per day.

What causes lightning to occur?

Clouds become electrified when ice crystals within them are vigorously mixed by strong columns of rising air, also known as updrafts. The stronger the updraft, the more electrified the thunderstorm can get. Lightning is needed to balance out the charge differences.

Lightning occurs when a charged part of a cloud connects with something of an opposite charge. For example, when the difference in charge is sufficiently large, a positive part of a cloud can make a connection to a negatively-charged part of another cloud, to an area within the same cloud, or it can connect with the ground. The same is true for negatively-charged parts of a cloud. Only the cloud-to-ground lightning discharges are dangerous to us on the ground.

How harmful can lightning be to humans?

So far in 2019, lightning has killed 12 people in the United States, three of them in Florida. Florida is historically the deadliest state when it comes to lightning strikes because of the frequency of lightning, the dense population, and a tendency for people to be outdoors. Over the last decade, 284 people have been killed by lightning in the U.S. and 78 percent of them were male. While lightning can certainly be deadly, roughly 90 percent of lightning strike victims actually survive the encounter, though often with mental and/or physical disabilities.

Can electricity from lightning travel through things?

When lightning hits a tree, or the ground, it doesn't just stop at that point. The current spreads out horizontally and downward until it's dissipated. You can be as much as 100 feet away from where a lightning bolt strikes and still feel a jolt (or worse). It will travel along tree roots, metal pipes, wires, and just wet soil. You're dealing with a sudden injection of perhaps 20,000 amps and  100,000,000 volts, so it takes some distance to dissipate that energy.

Where is the safest place to be when it is lightning?

The safest place to be during a thunderstorm is indoors, away from plumbing and appliances. A close lightning strike can find your pipes and any water coming out of them, so it’s best to stay out of the shower when there is lightning.

Also, if you’re caught outdoors, you absolutely do not want to take shelter near or under a tree. Trees are great attractors of lightning. If you are outside and get caught in a thunderstorm, either rush indoors or to a car if you can, or squat down with your feet together as a last resort. It can be terrifying and you'll get drenched, but it could save your life.

WeatherSTEM units on the University’s Coral Gables, medical and marine campuses continually scan atmospheric conditions to provide important data on weather conditions and much more. Students on the Coral Gables campus should be aware there is an outdoor siren that goes off when lightning is expected within the immediate area. The siren sounds like a distant, steady car horn that continues for about 10 seconds. This is a signal to anyone presently outdoors that lightning is imminent and that they should seek shelter indoors as soon as possible. When the threat has passed, the siren will sound a series of short blasts to let the community know there is no longer a threat of lightning expected nearby.

The University’s Office of Emergency Management also has information available regarding severe weather events and preparedness. For more information on specific response to the most common campus hazards (including severe weather and lightning), visit the Office of Emergency Management website. The office also offers in-person All Hazards Emergency Preparedness trainings, available free to all UM faculty, staff and students. 

Faculty and staff can register for the training on ULearn by logging in, searching for “Hazards”, and registering for the specific date/time/location of their choosing. Students can register for the training at and selecting which date/time/location they prefer to attend.