HOW IT FORMS
Ice, hail and charge
Updrafts carry ice up while heavier hail falls. Collisions pass electrons to the hail, so the cloud base turns negative and the top positive, until the charge sparks.
See the numbersWHAT THE MET OFFICE SAYS
Hear thunder?
Head inside.
Lightning is a spark the size of a storm.
GET INSIDE at the first rumble
200–300k Lightning counts in a typical year
- Check the forecast first
- Buildings and cars, not trees
- Off hills, off water
- Simple moves, safer storms
Ice and hail rubbing together inside a thundercloud build up a huge electrical charge. When it lets go, the channel can reach 30,000 °C. UK safety advice boils down to one habit: get into a building or a car as soon as you hear it.
THE SHORT ANSWER
Shelter properly,
and do it early.
Most of the risk is outdoors.
The advice is about where you stand when a storm arrives.
HILLS
Come down off the top
The Met Office says to get off hills, ridges and peaks straight away and move to lower ground, then into a building or a car.
Check where you are
TREES
Not under a tree
RoSPA says one in four people struck by lightning are sheltering under trees. Isolated trees are exactly the wrong place to wait it out.
What to doA QUICK STORM CHECK
Where are you when
the thunder starts?
Pick a spot to see what the safety advice says. The bar shows how urgently the guidance says to move.
Based on Met Office and RoSPA lightning safety advice and the US National Weather Service. General information only.
FOUR HABITS TO TRY
Plan around storms,
not through them.
Most of this happens before you leave the house. A glance at the forecast does more than any trick in the field.
Check the forecast first
The Met Office suggests checking before any outdoor or water activity and rescheduling if thunderstorms are forecast.
Move at the first rumble
If you hear thunder outdoors, get into a building or a car. The US weather service says many casualties come from waiting too long.
Stay in for half an hour
RoSPA's 30/30 rule: shelter if flash to bang is 30 seconds or less, and stay put until 30 minutes after the last thunder.
Know it is safe to help
A person struck by lightning does not carry a charge. Call the emergency services and give first aid or CPR if you know how.
TWO NUMBERS WORTH KNOWING
Lightning is common.
Being hit is rare.
One figure on how often lightning comes down,
one on how many people it reaches.
200–300k
Lightning counts in a typical year
TORRO says the UK, Ireland and surrounding seas typically see 200,000 to 300,000 lightning counts a year. On 28 June 2012 alone there were 64,000 strikes.
UK LIGHTNING · TORRO
30–60 people
People struck in Britain each year
RoSPA says 30 to 60 people are struck by lightning each year in Britain and on average 3 of these strikes are fatal. 80% of victims are male.
PEOPLE STRUCK · RoSPA
TORRO says storms can happen anywhere in the UK in any month, but are most common in south-east England and from May to August.
MYTHS TO DROP
It can strike
the same place twice.
Lightning often hits the same spot again, especially tall, pointed, isolated things. The US National Weather Service says the Empire State Building is hit about 23 times a year.
It can also strike well away from the rain: the weather service says lightning often strikes more than three miles from the centre of a storm, which is why a clear patch overhead is not a sign that it is safe.
Questions
Questions people ask
How does lightning form?
Updrafts carry ice particles up inside a storm cloud while heavier hail falls back through it. Collisions pass electrons to the hail, giving the lower cloud a negative charge and the top a positive one, and lightning is the discharge.
How hot is lightning?
The Met Office says a lightning channel can reach temperatures of up to 30,000 °C almost instantly. The bolt itself is only about 2 to 3 cm wide.
How do I tell how far away a storm is?
Count the seconds between the flash and the thunder. The Met Office says divide by five for an approximate distance in miles, or by three for kilometres.
Is it safe to stay in a car?
Yes. The Met Office names a car as a safe, enclosed shelter, and RoSPA lists a motor vehicle alongside a large building.
Should I crouch down if I am caught in the open?
UK advice describes a low crouch only as a last resort when there is no shelter. The US National Weather Service stresses that crouching does not make you safe, so keep moving towards a building or a car.
Where the facts come from
Updated