Cumulonimbus clouds can be up to 10 km high. Here we see three of them lined up together and lit up by the setting sun. Strong winds in the upper atmosphere will flatten the top of the clouds into an anvil-like shape. Cumulonimbus clouds are thunderstorm clouds and can bring heavy rain, snow, hail, lightning, and sometimes tornadoes
The electric charges which build up in thunderclouds are huge. A lightning protection system has to be able to handle surges of up to 120 thousand amps, voltage of up to one billion volts, and temperatures which can melt glass. Positively charged lightning, which comes from the top of the cloud, can be up to ten times more powerful.
Around the rod of a lightning protection system there will sometimes be a glow, caused by the ionization of the air around it, however it doesn’t mean that a lightning strike is imminent.
If you are standing outside during a thunderstorm, you have an increased chance of being struck by lightning. Your wet skin will act as the lightning conductor carrying the charge to the ground. Unlike other types of electrical shock, lightning will follow the outside of your skin to the ground, rather than travelling through your body.
To reduce your chances of being struck, stay indoors during lightning storms. If you can’t get indoors, avoid tall objects, such as trees, and avoid open areas where you are the tallest object. And don’t carry anything long and metallic, such as a ladder or a golf club.