What causes thunder and lightning? And how to stay safe in UK thunderstorms this week

While the weather across the UK has enjoyed sunshine and clear skies, it’s typical for British weather to change in the blink of an eye.

For England, the Met Office has issued yellow weather warnings for thunderstorms across much of the country this week.

This is everything you need to know about thunder and lightning, and how to stay safe.

What does the yellow weather warning mean?

In regards to thunderstorms, the yellow weather warning from the Met Office says that you should expect:

- A small chance that homes and businesses could be flooded quickly, with damage to some buildings from floodwater, lightning strikes, hail and strong winds

- A chance of delays and some cancellations to train and bus services

- Difficult driving conditions due to spray, sudden flooding and possible road closures

- A small chance that some communities may become cut off by flooded roads

- A slight chance that power cuts could occur and other services to some homes and businesses could be lost

What creates 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 negatively charged ice crystals sink to the bottom.

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What’s 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.

How can I 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.

The Met Office states that both of those facts “are false, as lightning strikes the best conductor on the ground - whether it has been struck before or not”.

There are steps that you can take before, and during, a thunderstorm to help keep you safe.

What to do before a thunderstorm

Prior to a thunderstorm, you should unplug any non-essential appliances if you’re not already using a surge protector, as lightning can cause power surges.

You should also seek shelter where possible - the Met Office states that if you can hear thunder, you’re already within range of where the next ground flash could occur.

What to do during a thunderstorm

During the thunderstorm itself, you should avoid using a landline phone, unless it’s an emergency, as telephone lines can conduct electricity.

If you’re outside during a thunderstorm, avoid water and find a low lying open place that is a safe distance away from the likes of trees, poles or metal objects.

You should be aware of metal objects around you that could act as conductors, 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 that you “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” - which means you should not lie down.

If you feel your hair standing up on end, drop to the previously described position immediately.

After the thunderstorm has run its course you should avoid any downed power lines or broken cables.