A lot of members of my community pool are having a dispute we need your help in rectifying. Here it is: Every Friday night our pool is supose to stay open until 9:30, but ALWAYS closes early due to so called "lightning". This so called "lightning" even ocurs on clear nights with little or no cloud cover. What we think the lifeguards are actually seeing is "inner cloud lightning" from far-far away. I realize sky to ground lighnting is extremely hazardous, but what about this type of ocurrance? We think our pool lifeguards use this as an excuse to close the pool early, and that the severity to life and limb is greatly exagerated. Please explain.
Posted July 3, 2007
MIKE MOSS SAYS: Mike, It may be a good idea to consider having a clear, concise lightning safety plan developed and written down that everyone can agree on. Generally, safety experts recommend that if thunder is audible, it is time to consider moving to a safe location, and that facilities such as pools, athletic fields and so on remain clear until 30 minutes have passed since the last thunder was heard. The rationale here is that atmospheric refraction of the sound waves associated with thunder tends to make them inauduble beyond about ten miles away, and in rare cases lightning has been known to strike as much as ten miles from the parent storm. The threat is considered critical when cloud to ground strikes are occuring within six miles. This can be estimated by timing "flash to bang" and noting if the thunder occurs 30 seconds or less after the lightning flash. There are times at night when distant lightning may be visible from much more than ten miles away - unless thunder can be heard, this is probably not a serious threat (some common sense applies here, of course - if some kind of ambient noise in the local area would mask the sound of thunder, be extra cautious about visible lightning, etc).
Here are some addresses where you can find more detail on lightning safety.