Calculating how far a storm is is quite simple and very necessary. This can help you to seek refuge if, by surprise, the sky darkens and the first lightning appear.

The first step to calculate it is to count the seconds that pass since the light is produced until you hear the thunder. This difference in time is due to the light traveling at a speed of 300.000km per second and the sound, in the air, at only 340m per second. Therefore, to calculate the distance to which a storm is located, we apply the following formula:

Distance = elapsed seconds (from when you see the lightning until you hear the thunder) /3

To know if the storm is approaching or moving away, we let 2 minutes pass and we calculate it again. If in the second calculation the result is lower than the previous one, it means that the storm is coming toward us. If the second result is greater, the storm is moving away.

There is a good measure of prevention in case of hearing thunder or seeing the lightnings. This rule is know as 30-30 Rule.

This rule is to seek refuge if less than 30 seconds pass between the lightning and thunder, and go outdoors only after 30 minutes have passed since the last thunder.