2013-07-12 / In the Know

When thunder roars, go indoors

By John Jensenius Special contributor

The title of this article is a public education catchphrase that the National Weather Service uses to educate the public about the dangers of thunderstorms. The idea is to stop outdoor activities and seek shelter immediately in a substantial building or a hard-topped metal vehicle as soon as you hear thunder because lightning could strike at any time.

It’s a common situation. A thunderstorm is approaching or nearby. Are conditions safe, or is it time to head for safety? Not wanting to appear overly cautious, many people wait far too long before reacting to this potentially deadly weather threat. To promote a better understanding of the threats of lightning, the National Weather Service (NWS) and the National Oceanic and Atmospheric Administration (NOAA), in conjunction with lightning experts across the country, sponsor a Lightning Safety Awareness Week each year.

The goal of this campaign is to give people a better understanding of the dangers of lightning so that they make safer decisions when thunderstorms threaten. The safety recommendations outlined during the week are based on lightning research and the lessons learned from the unfortunate experiences of thousands of lightning strike victims.

Several survivors have joined with the NWS in this educational effort. As the survivors can attest, knowledge of lightning safety is something that should be learned through education, not through experience. In order to understand the lightning threat, some basic information is required.

Thunderstorms produce two types of lightning flashes, negative and positive. While both types are deadly, the characteristics of the two types of flashes are quite different.

Of the two, negative flashes occur more frequently, usually under or near the base of the thunderstorm where rain is falling. In contrast, positive flashes generally occur away from the center of the storm and often in areas where rain is not falling. Because these positive flashes occur where the lightning threat is perceived to be low or nonexistent, they often catch people by surprise. Each year across the United States, thunderstorms produce an estimated 25 million cloud-to-ground flashes of lightning – each one of those flashes is a potential killer.

Based on cases documented by the National Weather Service over the past 30 years, an average of 73 people are killed by lightning each year and hundreds more are injured, some suffering devastating neurological injuries that persist for the rest of their lives. A growing percentage of those struck are involved in outside recreational activities. When lightning is in the area, the sooner that activities are stopped and people get to a safe place, the greater the level of safety. In general, a significant lightning threat extends outward from the base of a thunderstorm cloud about 6 to 10 miles. Therefore, people should move to a safe place when a thunderstorm is 6 to 10 miles away. Thunder can usually be heard for a distance of about 10 miles provided that there is no background noise.

Traffic, wind, and precipitation may limit the ability to hear thunder to less than 10 miles. If you hear thunder, though, it’s a safe bet that the storm is within 10 miles. If the time between lightning and corresponding thunder is 30 seconds or less, this would indicate the thunderstorm is six miles away or less. Additionally, activities should be halted if the sky looks threatening. Thunderstorms can develop directly overhead and some storms may develop lightning just as they move into an area. There is no place outside that is safe in or near a thunderstorm. Consequently, people need to stop what they are doing and get to a safe place immediately. Small outdoor buildings, including dugouts, rain shelters, sheds, etc., are not safe.

Substantial buildings with wiring and plumbing provide the greatest amount of protection. Office buildings, schools and homes are examples of buildings that would offer good protection. Once inside, stay away from windows and doors and anything that conducts electricity such as corded phones, wiring, plumbing and anything connected to these.

In the absence of a substantial building, a hard-topped metal vehicle with the windows closed provides good protection.

Occupants should avoid contact with metal in the vehicle and, to the extent possible, move away from windows. Because electrical charges can linger in clouds after a thunderstorm has passed, experts agree that people should wait at least 30 minutes after the storm before resuming outdoor activities. Most victims can survive a lightning strike; however, medical attention may be needed immediately. Call 911 for medical help. Victims do not carry an electrical charge and should be attended to at once. In many cases, the victim’s heart and/or breathing may have stopped and CPR may be needed to revive them.

The victim should continue to be monitored until medical help arrives; heart and/or respiratory problems could persist, or the victim could go into shock. If possible, move the victim to a safer place away from the threat of another lightning strike. For more information on lightning and lightning safety visit the National Weather Service at www.lightningsafety.noaa.gov or call the NWS forecast office in Gray at 688-3216.

John Jenseniua is a warning coordination meteorologist for the National Weather Service in Gray.

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