Here's what causes thunder and lightning - as the UK prepares for epic storms

Tuesday, 11th August 2020, 12:17 pm
Updated Tuesday, 11th August 2020, 12:17 pm
Thunderstorms happen when the atmosphere is unstable (Photo: Shutterstock)
Thunderstorms happen when the atmosphere is unstable (Photo: Shutterstock)

The Met Office has issued yellow weather warnings across the UK for thunderstorms - but what exactly causes the phenomenon of thunder and lightning?

This is how thunder and lightning is created - and what to do if you find yourself caught in a storm.

What is a thundercloud?

The Met Office explains that “thunderstorms develop when the atmosphere is unstable” and this occurs when “warm air exists underneath much colder air”.

As the warm air rises, it cools and condenses to create moisture and subsequently a cloud.

If the conditions are right, the cloud will build into a cumulonimbus cloud - the type needed to produce thunder and lightning.

Within a cumulonimbus cloud, there are updraughts and downdraughts of air.

The updraughts carry moisture and water droplets up so high that they freeze and turn into ice crystals. Once they become too heavy to be supported by the updraughts, they fall as hail.

During this process, the ice particles bump against each other and give off positive and negative electrical charges.

The lighter positively-charged ice crystals are forced up to the top of the cloud whereas the heavier negative charged ice crystals sink to the bottom.

What causes thunder and lightning?

The negative charged ice crystals are attracted to the positive charge, as well as to charges in nearby clouds and positive charges on the ground.

When this attraction is strong enough, the charges join together and discharge, creating flashes of lightning.

“Lightning is a large electrical spark caused by the negative charges moving from one place to another,” the Weather Channel explains.

Thunder occurs due to the quick expansion and heating of the air caused by lightning.

Thunderstorm warnings in the UK

Currently, the Met Office displays a yellow weather warning across the majority of the UK for thunderstorms.

The yellow warning states that “some places are likely to see severe thunderstorms” but there is “significant uncertainty in location and timing”.

This is what the Met Office says to expect:

  • The small chance that homes and businesses could be flooded quickly, with damage to some buildings from floodwater, lightning strikes and large hail
  • Where flooding or lightning strikes occur, there is a chance of delays and some cancellations to public transport
  • Sprays and sudden flooding could create difficult driving conditions and increase chances of accidents
  • The slight chance that power cuts could occurs and that other services to homes and businesses could be lost
  • The small change of fast flowing or deep flood water could cause danger to life

How to stay safe in a thunderstorm

There are many myths and misconceptions around thunderstorms which could lead to people getting hurt, such as the idea that lightning never strikes the same place twice, or that it always strikes the tallest object.

“Both are false, as lightning strikes the best conductor on the ground - whether it has been struck before or not,” states the Met Office.

There are various steps you can take before, during and after a thunderstorm to keep yourself safe.

Before the thunderstorm:

  • Because lightning can cause power surges, you should unplug any non-essential appliances if you’re not already using a surge protector
  • Seek shelter where possible - the Met Office says that if you can hear thunder, then you’re already within range of where the next ground flash could occur

During the thunderstorm:

  • Avoid using a landline phone, unless in an emergency, as telephone lines can conduct electricity
  • If you’re outside, avoid water and find a low lying open place that is a safe distance away from trees, poles or metal objects
  • Be aware of metal objects that could conduct or attract lightning, such as golf clubs, fishing rods, umbrellas, bikes and wire fencing
  • If you’re stuck in an exposed location, the Met Office recommends to “squat close to the ground, with hands on knees and with [your] head tucked between them” and to “try and touch as little of the ground with your body as possible”, so do not lie down
  • If you feel your hair stand up on end, drop to the previously described position immediately

After the thunderstorm, avoid downed power lines or broken cables.