Summer is the most dangerous season for lightning deaths and injuries. Nearly 100 people die from lightning strikes each year, and hundreds are injured. If you see lightning or hear thunder, you are a potential target for a lightning strike. For each five seconds you count between seeing the lightning flash and hearing the thunder, there is one mile between you and that lightning strike. Pools that have obstructed views should evacuate anytime thunder is heard.
Thunder usually becomes audible within ten miles of the thunderstorm.
A developing storm may provide no advance warning before the first lightning strike. There should be a well grounded, enclosed and sturdy building handy for everyone. If not, evacuate the pool sooner. Include the extra time needed to get people out of the pool and to the building in your evacuation plan. Wait thirty minutes from the last time thunder is heard before reopening the pool.