|Meteorologist Jim Woodmencey|
(Note: This is re-posted here from the original article that appeared in Jackson Hole News & Guide Mountain Weather column on July 9, 2014.)
In my last Mountain Weather column (June 25) I gave you a few facts and statistics about lightning related incidents, both nationally and locally. This week I will give you some more practical knowledge about thunderstorms and lightning, and what to do if you find yourself outdoors during a dangerous thunderstorm.
The first thing you need to do is follow the weather forecast, every day, to see what the chances are for thunderstorms. Have some idea if thunderstorms are going to be a threat, and get the latest updated forecast, before you head out the door.
Once out the door, keep an eye on the sky and see how the clouds are developing as the day progresses. If they are growing taller, and the bases of the clouds are getting darker, then thunderstorms and their accompanying lightning may be imminent. Remember: what you observe always trumps what the forecast said!
When to Hide
As soon as you can hear the thunder, lightning is close enough to strike, and it is time to seek shelter. Lightning can be seen from about 15 miles away, and thunder can be heard up to about 10 miles away, on a good day. In a canyon, or out in the wind, it may not be heard until much closer.
You can estimate how far away the lightning is by counting the seconds between when you see the flash of lightning and when you hear the thunder. Count in seconds (one-thousand-one, one-thousand two, etc.). Five seconds equals one mile. If you count to 25, that means the lightning is 5 miles away, which is actually close enough to be able to reach out and kill you.
Don’t wait for it to start raining before you think about seeking shelter, or for the first bolt to hit nearby, as most people tend to do.
Where to Hide
If you can get to a building, or a car, that is the safest place to be. Picnic shelters, a gazebo, a dugout at the ball field, are NOT good shelters from lightning. Your car is, not because the tires insulate, but because the frame and body take all the electrical current and disperses it. Get in the car, don’t touch the doorframe, and wait it out.
If you find yourself stuck outside, far from the car or a building, don’t run underneath the biggest, loneliest looking tree for shelter. A better option is to get into a stand of trees of similar height, and make sure you are not standing on top of any tree roots. If all else fails, get into a low spot in the terrain, that is not a watercourse, and crouch down.
If you are in the mountains, get down off the higher ridgetops, get into a gully or low spot between ridges, but don’t sit in a gully that might become a running watercourse. Also, DO NOT get under an overhanging rock or in a cave. Electricity will often jump the gap that you are sitting or standing in when lightning strikes nearby.
If you are on a lake or river, get out of the water, and off the boat. Water is a great conductor of electricity! Get to shore and find a stand of similar sized trees to wait it out.
How to Hide
The absolute best thing you can do to prevent injuries from lightning striking nearby is: KEEP YOUR FEET TOGETHER.
Keeping your feet together will help prevent dangerous ground currents from running up through one leg and exiting down the other. You may feel a bump under your feet as the ground current passes, if both feet are together, but it is unlikely that you would receive a serious electrical injury. Your other option is to sit on the ground with your legs crossed, Indian-style.
This is why lightning, due to the difference in voltage of the ground current between each leg, frequently kills cows and sheep. They don’t have the ability, or the sense, to put all four of their feet together.
Also, get away from any metal objects, or empty your pack of any metal. You might want to also take off any metal jewelry.
Lastly, don’t huddle together in a group, as cows and sheep also tend to do during thunderstorms. Spread out, at least 25-feet feet apart, 50 feet of separation from your companions is even better.
A lightning strike has about the same kill-casualty radius as a standard Army-issue hand grenade. Either one can kill you and everyone that is within a 25-foot radius of the explosive, and injure you or everyone out to a 50-foot radius.
You should stay in a safe location or position for at least 20 to 30 minutes after the last lightning bolt strikes, to make sure the thunderstorm is a safe distance away. That’s another thing that is hard to get people to do. We usually come back out to play way too soon.
TIMING LIGHTNING to THUNDER
Lightning travels at the speed of light, which is faster than the speed of sound that Thunder travels. Therefore, lightning is seen before the thunder is heard. You can time how far away the lightning is by counting, in seconds (one-thousand-one, one-thousand-two, etc.), From the time you see the flash, until the time you hear the thunder.
Take the number of seconds and divide by 5 to calculate the distance the lightning is from you in miles. Seconds Counted / 5 Seconds per mile = Number of Miles Away.
25 seconds = 5 miles away. 5 seconds = one mile away. 1 second = less than a quarter mile away.
20/20 Lightning Rule
If the time between the lightning flash and the thunder is 20 seconds or less, then the lightning bolt was less than 5 miles from your location. It is time to seek shelter IMMEDIATELY!
After the last lightning bolt is seen, give it at least 20 minutes until you return to any exposed area. ( A “30/30” Rule is even safer!)
Jim is the chief meteorologist at mountainweather.com and has been forecasting the weather in Jackson Hole and the Teton Mountains for over 20 years.