Lightning

The current message

The NWS states its position in three sentences, and they are worth having exactly:

There is no safe place outside when thunderstorms are in the area.
If you hear thunder, you are likely within striking distance of the
storm. Just remember, When Thunder Roars, Go Indoors.

Lightning strikes the United States about 25 million times a year and kills about 20 people annually, with hundreds more severely injured. Published averages differ depending on the years they cover and they have been falling for decades, so quote the figure with its source rather than from memory.

Bolt from the blue

Lightning can strike more than ten miles from the rain that produced it, under clear sky. Which produces the statistic that should change your behaviour more than any other in this lesson: more than half of lightning deaths happen after the storm has passed.

The reason is behavioural rather than meteorological. People wait out the rain, the rain stops, they come out, and the storm is still close enough. Wait 30 minutes after the last thunder before going back outside, and restart the thirty minutes if you hear thunder again.

Vehicles

A hard-topped metal vehicle with the windows up is genuinely good protection, and almost everybody believes it for the wrong reason. The NWS is explicit about the mechanism:

"the outer metal shell of hard-topped metal vehicles does provide protection to those inside a vehicle with the windows closed." The current runs over the shell and then, in the NWS's own description of a strike, through the tyres to the ground. The tyres are part of the path, not an insulator.

Five ways it reaches you

Direct strike

The flash hits you. Rarest, and the most often imagined.

Side flash

The flash hits something taller nearby, usually a tree, and jumps sideways to you. This is why sheltering under a tree is not shelter.

Ground current

The current spreads out through the ground from the strike point and passes up one leg and down the other. This kills the most people, and it is why there is no safe distance from a strike point in the open.

Conduction

Along wiring, plumbing, fences and metal structures, which can carry it a very long way indoors. The reason to stay off a corded phone and out of the shower in a storm.

Upward streamer

The upward discharge from an object on the ground that does not end up completing the main channel. Still carries enough current to injure or kill.

If somebody is struck

Check your own safety first, because the storm that struck them is still there and may strike again in the same place. Move the casualty if you can do it safely and quickly.