Nothing ruins a summer cookout, dip in the pool, or camping trip like a thunderstorm.

If you are outdoors when a thunderstorm rolls up, it can be tempting to stall as long as possible before going indoors. But how do you know when it's time to stop what you're doing and head inside? Keep a lookout for certain signs; they'll warn you when it's time to seek shelter indoors and when lightning may be about to strike.

Signs of Lightning

Cloud-to-ground lightning is nearby if you notice one or more of these early signs. Seek shelter immediately to reduce the risk of lightning injury or even death.

A rapidly growing cumulonimbus cloud. Although cumulonimbus clouds appear bright white and form in sunny skies, don't be fooled—they're the beginning stage of a developing thunderstorm. If you notice them growing taller and taller in the sky, you can rest assured that a storm is in the making and headed your way.

Although cumulonimbus clouds appear bright white and form in sunny skies, don't be fooled—they're the beginning stage of a developing thunderstorm. If you notice them growing taller and taller in the sky, you can rest assured that a storm is in the making and headed your way. Increasing winds and a darkening sky. These are telltale signs of an approaching storm.

These are telltale signs of an approaching storm. Audible thunder. Thunder is the sound created by lightning, so if thunder can be heard, lightning is near. You can determine how near (in miles) by counting the number of seconds between a flash of lightning and a thunderclap and dividing that number by five.

Thunder is the sound created by lightning, so if thunder can be heard, lightning is near. You can determine how near (in miles) by counting the number of seconds between a flash of lightning and a thunderclap and dividing that number by five. A severe thunderstorm warning. The National Weather Service issues a severe thunderstorm warning whenever severe storms have been detected on weather radar or confirmed by storm spotters. Cloud-to-ground lightning is often the main threat of such storms.

Lightning always occurs during thunderstorms, but it isn't necessary for a storm to be directly overhead for you to be in danger of a lightning strike. The threat of lightning actually starts as a thunderstorm approaches, peaks when the storm is overhead, and then gradually diminishes as the storm moves away.

Where to Seek Shelter

At the first sign of approaching lightning, you should quickly seek shelter, ideally in an enclosed building or other structure, away from windows. If you're at home, you may want to retreat to a central room or closet. If you cannot find shelter inside, the next best option is a vehicle with all of the windows rolled up. If for whatever reason, you are stuck outside, you should make sure to stand away from trees and other tall objects. Keep away from water and anything that is wet, as water is a strong conductor of electricity.

Signs of an Immediate Strike

When lightning strikes you or the area immediately nearby, you may experience one or more of these warning signs a few seconds beforehand.

Hair standing on end

Tingling skin

A metallic taste in your mouth

The smell of chlorine (this is ozone, which is produced when nitrogen oxides from lightning interact with other chemicals and sunlight)

Sweaty palms

A vibrating, buzzing, or crackling sound coming from metal objects around you

If you notice any of these signs, it may be too late to avoid being struck and possibly injured or killed. However, if you find that you do have time to react, you should run as fast as you can to a safer location. Running limits the amount of time that both of your feet are on the ground at any given moment, reducing the threat from ground current (lightning that travels outward from the strike point along the ground surface).