How do thunderstorms form and why do thunderstorms occur in summer?

ITV Weather Presenter Becky Mantin explains the science behind how thunderstorms form

The weather during the summer months can be very dramatic, with plenty of heat and energy in the air producing some big thunderstorms, but how do they form?

It is all to do with heat and moisture.

As air rises it cools, causing the water vapour in the air to cool and condense into liquid water droplets and make clouds.

Some clouds are small and produce no rain, some are really high and made of ice, and some are huge cumulonimbus clouds that produce hail and thunder.

A cumulonimbus cloud

Within one of these thunderclouds there are huge currents of air moving up and down.

These currents drag heat and moisture into the cloud, allowing them to grow in size.

The moving air carries water droplets to the top of the cloud (which can be 20,000 to 40,000 feet above the surface) where they freeze into balls of ice - what we know as hail.

As hail and other, smaller ice particles bump against each other they become electrically charged.

The hail gets a negative charge and the ice particles become positive.

The heavy hail sinks to the base of the cloud and the lighter ice particles are drawn to the top on those air currents.

The cumulonimbus cloud effectively ends up like a giant battery.

Positive and negative charges within a thunderstorm

As the negative charge at the bottom of the cloud increases, the energy becomes too much for the cloud to contain and has to discharge somehow.

This is when we see lightning and hear thunder - either from the base of the cloud to the ground, or within the cloud itself.

How powerful is lightning?

Lightning travels at 270,000 mph. As it moves through the air it creates a huge amount of heat almost instantly - some 30,000°C some five times hotter than the surface of the sun.

Each lightning bolt is around 300 million volts of power (30,000 amps). Compared to your standard 240 volt plug socket at home.

One lighting bolt has enough energy to power a lightbulb for a year!

What is thunder?

Thunder is sound we hear as the air rapidly expands from lightning heating it. The closer you are to lightning the louder it is.

If you're over 20km away from a thunderstorm, you can see lightning but not hear the thunder as the atmosphere has the ability to muffle the sound.

What impacts do Thunderstorms bring?

Thunderstorms have the ability to produce property damage by flooding from short intense rainfall events and fire produced from lightning.

Thunderstorm facts

  • There are around 3 million lightning strikes every day around the globe

  • A lightning bolt strikes Earth every 44 seconds on average

  • If you count in seconds the gap between seeing lightning and hearing thunder and divide this by 5 it will roughly tell you how far away a thunderstorm is in miles to you.