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Understanding Lightning & Thunder on the Trail

When hiking, particularly above treeline, the importance of lightning awareness cannot be understated. Understanding more about lightning and thunder can help keep you and your trail family safe.

Paul Bodnar     Educational       7/14/2020

The (Quick & Dirty) Science Behind Lightning

The speed of light is 670,616,629 mph, so when you see a lightning strike you’re perceiving it practically instantaneously. Every strike heats up the surrounding air to between 18,000 to 60,000 degrees Fahrenheit (two to six times the temperature of the surface of the sun), which causes the surrounding air to rapidly expand and then suddenly contract, resulting in a sound wave – thunder.

A lightning strike on a dark mountain.

Distance of a Storm

If you don’t hear any thunder but see a lightning strike, the lightning is likely over 10 miles away from you, as the sound wave is being absorbed before reaching out. As such, if you see a lightning strike but don’t hear the corresponding thunder you are likely not in immediate danger. Storms move quickly, however, and it’s important to hike off of exposed ridges, passes, and summits and to prepare for the storm to potentially reach you soon.  

If you do hear thunder, you are within about 10 miles of the lightning strike and should seek immediate protection from a lightning strike.

The American Hiking Society has a downloadable pdf titled Lightning Safety that outlines specific precautions that should be taken.

Lightning Safety Guidelines

Always check the weather forecast before leaving town, if conditions are not safe on trail find a safe place to shelter in town.

Always descend from peaks, ridges or elevated areas when in a storm or when one is approaching.

A safe structure is a building that is fully enclosed and has electricity and plumbing. A public library would be a great place to temporarily shelter in town if you can’t find a hostel or motel. Structures like trail shelters, patios, tents, or sheds are not safe during a lightning storm. 

If you can not find a suitable shelter on trail seek protection by immediately reducing elevation, find a valley or depression in the area and avoid isolated trees or tall structures. 

Never lie flat on the ground during a lightning storm. You should crouch on the ground with your feet together and with your weight on the balls of your feet.

The tips above are not comprehensive. Please review detailed information from the National Oceanic and Atmospheric Administration (NOAA) and the American Hiking Society before your next outdoor adventure.

A lightning strike in the distance past some mountains and hills.
A lightning strike on a dark mountain.

To determine the approximate distance (in miles) of lightning from you, count the number of seconds between the observed lightning flash and the sound of thunder, then divide this number by five. (See equation below.)

Approximate Distance Away (miles) = number of seconds between flash and sound / 5

Use the above equation to calculate a series of distances from a few different strikes and you will be able to determine if the thunderstorm is stationary, moving toward you or away from you. If the calculated distance doesn’t change between lightning strikes you can assume the storm is stationary. If the distance gets larger between lightning strikes you can assume the storm is moving away from you. If the distance gets shorter between lightning strikes the storm is moving closer to you and storm precautions should be observed. 

Real Trail Story: Safety Over Miles

By Dahn Pratt

While hiking on the Continental Divide, I was on a major time crunch and often found myself on exposed ridge-lines during thunderstorms. This arbitrary time-frame forced me into dangerous situations that I’ll never repeat again. On the Montana/Idaho border I was “threading the needle” through multiple thunderstorms trying to make forward progress without considering my safety. As thunder shattered all around me, I ran for hours trying to avoid the ominous clouds shooting off lightning every couple of seconds. Being up high, above treeline, was very stupid as it began to hail furiously. The lightning and thunder were milliseconds apart and I felt an electric surge up my legs from a ground strike a stone’s throw away. The experience caused some major post traumatic stress for me on the hike and forced me to adopt a motto, “safety over miles” when approaching a climb, especially later in the day and when there were less than ideal conditions. Never jeopardize your safety for the sake of forward progress!

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Showers Lake Vista, Tahoe Rim Trail
Photo courtesy of the Tahoe Rim Trail Association
A lake reflects a nearby wildflower meadow and trees.
Showers Lake Vista, Tahoe Rim Trail
Photo courtesy of the Tahoe Rim Trail Association

Trail guides that get you to places you’ve dreamed of.

As the makers of Guthook Guides, Bikepacking Guides, and Cyclewayz, we help you navigate the most popular trails around the world on your smartphone. Our hiking guides and biking guides work completely offline. Let Guthook guide your next adventure!

Download our popular hiking and biking guides!
About the Authors
A man wearing an Arizona Trail baseball cap stands in a field in front of a mountain.

Paul Bodnar

Paul has always liked hiking and thru-hiked the Pacific Crest Trail in 1997 after college. After years of working in chemistry, he wanted to create a career involving the outdoors, so he hiked the Pacific Crest Trail again in 2010 to do research for his guide book Pocket PCT. He realized that creating a smartphone app for navigating the outdoors would make it easier to keep the data current and provide a better way to navigate. While hiking with Ryan (aka Guthook) in 2010, they decided to work together to create the first comprehensive smartphone guide for the Pacific Crest Trail. Now with the help of a team of great people they have created over 50 guides for trails around the world.

Dahn Pratt

Dahn began collecting trail data for Atlas Guides in 2017 on his 10,000 mile project called Chasing Summer. The most recent data for the Te Araroa, Pacific Crest Trail, Continental Divide Trail, Jordan Trail and Israel National Trail all came from Dahn. Now you will find Dahn on the office side of Atlas Guides doing all kinds of things, like data analytics, data processing, customer support, and more. When he is not hiking he can be found camping, or making bad jokes.