There is one undeniable fact which has proven to be a supportive basis for the continued use and expansion of lightning warning systems at all outdoor venues. The lightning death statistics, which have averaged 100 deaths in the United States from the 1950's through 1992, have changed in a statistically significant manner. Due to the increased use of such systems and educational efforts from the United States Golf Association, universities, schools, and municipalities, the death average has steadily decreased to the all-time low of 29 in 2013. If this statistic for 2013 lightning deaths is confirmed, then the efforts of all of these groups deserve credit for improving lightning awareness in the United States.
There are two technologies which compete for the limited resources available in today's lightning warning marketplace: These are lightning detection and lightning prediction. These technologies are very different in the atmospheric analysis of lightning strikes which have already occurred and lightning prediction which provides warning prior to a strike. There are also lightning protection systems which are utilized to protect structures through the use of approved air terminals in accordance with NFPA 780. Although this protective technology is necessary and valuable, lightning protection systems are not the subject of the article.
Lightning Detection Systems
Lightning detections systems are designed to advise a user when-or after-an actual strike has occurred. Within a range of up to 10 miles, depending on the geography and ambient local noise levels, the human eyes and ears are the best detection system available. If you are looking in the direction of a lightning strike, you will see it immediately because there are no electronic processing or internetrelated delays. You will hear the thunder from that strike with the delay between the visible strike and the initial sound of thunder being about five seconds for every mile that strike occurred from you. As accurate as this system is, you can never know where the next strike will occur. Because there is no way detection can accurately "predict" where the next strike will occur, it would be prudent to immediately seek shelter upon seeing a strike. Any strike you see is already too close to assume you are a safe distance from the next strike.
Electronic detection systems are much better detecting actual strikes beyond ten miles. In fact, networked detection systems can see lightning in most locations in North America. These systems monitor the Earth's electromagnetic atmosphere which is disturbed when a lightning strike occurs, in the same way AM radio signals are disturbed by lightning. Various techniques are utilized to locate those strikes and filter out "false" alerts. These filters have been shown to actually filter out small strikes, which is essential, as even a small strike can be deadly.
According to the National Weather Service and Severe Storms Laboratories in Norman, OK, lightning can strike from a storm 15 miles in the distance. The Bolt-Out-Of-The- Blue can strike from over 50 miles away. Detection systems can't provide advance warning from such strikes. Many companies in the detection business claim that cloudto- cloud lightning strikes are an absolute precursor to cloud-to-ground strikes and use those inter-cloud strikes as a predictive tool for local warnings. Sometimes this type of lightning does provide pre-storm warnings, but more often than not it does not. This type of predictive technology is no more than a sophisticated guess. Lightning is not created in the Earth's electromagnetic field, it only disturbs it. Therefore only site-specific warnings can be considered "safe" through detection if the warning/shut-down is activated by lightning coming to ground at a distance of 20 miles. While this will not help with the Bolt-Out-Of-The-Blue, it would be a reasonable alternative to the commonly safety & security by Bob Dugan used dangerous distance to strike ranges of 5, 6, 8 or 10 miles. Of course, any range used in detection over 5 miles will result in many hours of delayed activities with no local storm activity.
LIGHTNING PREDICTION TECHNOLOGY
True lightning prediction systems do not use actual lightning strikes or the electromagnetic atmosphere to provide warnings for their customers. Rather, such systems watch for and measure, then analyze the Earth's electrostatic atmosphere. Through the utilization of sophisticated sensors and historical data, prediction systems do provide site specific warnings up to 2.5 miles from that sensor. Before you conclude that 2.5 miles is far less that 10 or more miles and too short for lightning warning, one needs to understand that 2.5 miles of prediction is totally different than 2.5 miles of detection.
Lightning is created when the changing atmospheric conditions create friction in the atmosphere. This friction creates fields of moving positive and negative ions. While such ions are always present in the atmosphere, they are normally in balance. In order for lightning to develop, these charges must grow and present the new unbalanced atmosphere with abnormal charge levels. When the level rises where there are two areas of positive and negative charges, present in the clouds and ground, and the electrical difference greatly increases, the opposite charges attract one another; when there is enough voltage to overcome the relatively dry atmosphere between the clouds and ground, you get lightning. The physics of electrical growth and recession during all storm activity permits advanced measurements of these interactions. Lightning prediction systems observe all changes and determine when a strike will occur, prior to the strike actually coming to ground. Typically, even a lightning strike that begins in a storm 12 miles away can take 10 to 20 minutes to develop a large enough electrostatic attraction to that point prior to the strike making its 12 mile trip. Detection will only tell you it just happened!
Lightning prediction is a time based system (proactive) while detection systems are distance based systems (reactive). Relating to a 2.5 mile radius of prediction, a typical warning time prior to a strike, even a first strike, is 12 to 20 minutes. This means that within that time period, a strike will occur within that 2.5 mile radius in 12 to 20 minutes. True prediction systems do not require any lightning anywhere in order to provide a timely warning for imminent lightning.
After a storm has passed can often be more dangerous that prior to a storms arrival. Frequently a storm will leave behind charges on the ground which could attract a lightning strike from the recently passed storm. While a prediction system will either see or not see such local delinquent charges, its decision to provide an all clear will be based only on the local electrostatic atmosphere. No energy present, no chance of a return strike. Detection systems will make a customer wait 30 minutes or more from the time of the last lightning strike within some distance assumed safe. There are many documented strikes returning from a storm already 15 or more miles away. More often than not, the prediction system will allow users a faster and safer resumption of activities.
Whether you choose a detection system or a prediction system, it is imperative you study the facts, the longevity of the company and the type of customers each has. Deciding to provide a lightning-safe environment for your students, staff and visitors is an important decision. This decision will ultimately contribute to the further improvement in the lightning statistics nationwide, a very worthwhile contribution.
is President of Thor Guard, Inc., and began with the company in 1988. Bob grew up in Albany, NY, and Pittsfield, Ma. Bob graduated from the College of the Holy Cross in 1975 and now resides in Marco Island, FL. For more information, email Bob at bdugan@ thorguard.com or call 954-835-0900.