Lightning Does Strike the Same Place Twice

Lightning never strikes the same place twice. It is one of the most comforting things people say, usually about bad luck, and it has one small problem: it is not true. According to the US National Weather Service, lightning often strikes the same place again and again, especially if that place is tall, pointy and standing on its own. The Empire State Building in New York is hit an average of 23 times a year.

Divide the year by 23 and that comes to roughly one strike every two and a bit weeks, although thunderstorms do not keep to a timetable. The building is not especially unlucky. It is simply very tall, very pointed and rather lonely at the top, and those, the weather service says, are exactly the things that decide where a bolt lands.

Here is the part that surprises most people. Metal has nothing to do with it. The same weather service lists the idea that metal attracts lightning as another myth: height, a pointy shape and isolation are the dominant factors, and the presence of metal makes no difference at all to where lightning strikes. Trees and mountains, which contain little or no metal, are struck many times a year. Metal does conduct electricity once lightning has hit, though, which is why it is still wise to keep away from fences and railings in a storm.

And a single flash does not even have to choose one spot. Many cloud-to-ground flashes fork on the way down and touch the earth in more than one place. Tests in the United States and Japan found this in at least half of negative flashes and in more than 70 per cent of positive ones. So lightning can, in a sense, strike two places at once, which spoils the saying from the other direction as well.

The reason tall things get hit lies in how a flash connects. Most, if not all, lightning starts inside the cloud. When a flash is heading for the ground, a channel works its way downwards in short steps, known as a stepped leader. When it gets within roughly a hundred yards of the surface, objects below, such as trees, bushes and buildings, begin sending up sparks of their own to meet it. Whichever spark connects first receives the huge surge of current. Tall objects are more likely than the ground around them to produce that connecting spark, which is why they are struck more often.

The National Severe Storms Laboratory adds that a particular patch of ground may have other reasons for being hit more than its neighbours: how salty or damp the soil is at the time, rock, standing water or pipes underground, or the shape of the land. Sometimes a repeat strike may simply be chance, because with so much lightning in the world, some of it is bound to land near where some already has. Either way, the old saying is better kept for talking about luck than about weather. Lightning is not looking for somewhere new. It simply likes a good tall target, and it will come back to one as often as it pleases.