Lightning and thunder always go together, because thunder is the sound that results from lightning. Lightning bolts are close to 30,000 degrees Celsius (54,000 degrees Fahrenheit), so the air in the atmosphere that they zip through becomes superheated and quickly expands.
That sound of expansion is called thunder, and on average it’s about 120 decibels (a chainsaw is 125, for reference). Sometimes you can see lightning but not hear the thunder, but that’s only because the lightning is too far away for you to hear it. Because light travels faster than sound, you always see lightning before hearing it.
- Start the count
When you see a flash of lightning, start counting. A stopwatch would be the most accurate way.
- Five seconds
The rule is that for every five seconds, the storm is roughly 1.6 kilometres (one mile) away.
- Do the maths
Stop counting after the thunder and do the maths. If the storm’s close, take the necessary precautions.