Thunder and lightning

Thunder and lighting are some of the most dramatic weather phenomena in the UK. They are caused through the formation of cumulonimbus clouds and usually last no more than half an hour.

A thunderstorm is a series of sudden electrical discharges resulting from atmospheric conditions. These discharges result in sudden flashes of light and trembling sound waves, commonly known as thunder and lightning.

Thunderstorms are associated with convective clouds and are often accompanied by precipitation.

How do thunderstorms form?

Thunderstorms develop when the atmosphere is unstable - this is when warm air exists underneath much colder air. As the warm air rises it cools and condenses forming small droplets of water vapour. If there is enough instability in the air, the updraft of warm air is rapid and the water vapour will quickly form a cumulonimbus clouds. Typically, these cumulonimbus clouds can form in under an hour.

As the warm air continues to rise, the water droplets combine to create larger droplets which freeze to form ice crystals. As result of circulating air in the clouds, water freezes on the surface of the droplet or crystal. Eventually the droplets become too heavy to be supported by the updraughts of air and they fall as hail.

As hail moves within the cloud it picks up a negative charge by rubbing against smaller positively charged ice crystals. A negative charge forms at the base of the cloud where the hail collects, while the lighter ice crystals remain near the top of the cloud and create a positive charge.

The negative charge is attracted to the Earth's surface and other clouds and objects and when the attraction becomes too strong, the positive and negative charges come together, or discharge, to balance the difference in a flash of lightning (sometimes known as a lightning strike or lightning bolt). The rapid expansion and heating of air caused by lightning produces the accompanying loud clap of thunder.

Transcript - How does lightning form and how do we detect it Transcript - How does lightning form and how do we detect it (PDF, 81 kB)

To view PDF documents you will need Adobe Reader.
Adobe Acrobat Reader

Where do thunderstorms form?

Thunderstorms are common occurrences on earth. It is estimated that a lightning strike hits somewhere on the earth's surface approximately 44 times every second, a total of nearly 1.4 billion lightning strikes every year.

Owing to the fact thunderstorms are created by intense heating of the earth's surface, they are most common in areas of the globe where the weather is hot and humid. Land masses therefore experience more storms than the oceans and they are also more frequent in tropical areas than the higher latitudes.

In the UK thunderstorms are most common over the East Midlands and the south-east.

Optical Transient Detector (OTD) and Lightning Imaging Sensor (LIS) image of global lightning (Source: NASA MSFC) Optical Transient Detector (OTD) and Lightning Imaging Sensor (LIS) image of global lightning (Source: NASA MSFC)

Facts about thunderstorms

  • A bolt of lightning lasts on average for about one 10,000th of a second but could light a 100 Watt light bulb for three months
  • Lightning travels through the air at around 270,000 mph - that's around 75 miles every second
  • Lightning is hotter than the surface of the sun reaching temperatures of around 30,000 °C
  • Thunderstorms can trigger asthma - find out more in  Thunderstorm-related asthma Thunderstorm-related asthma (PDF, 257 kB)
  • The island of Java is the most thundery place on earth with 220 days of thunderstorms every year.

Last updated: 4 December 2013