How far away is the storm? The flash-to-bang method can help.
When lightning is made by a storm the rapid heating and expansion of the air create the thunderclap. But because sound travels slower than light, there's a gap between seeing the lightning and hearing the thunder it produced. Using Distance = speed x time, by counting the seconds from seeing the lightning you can easily estimate how far away it is.
Conveniently, the speed of sound in air is about 330 metres/second. So depending on your unit preference:
Give it a try at a safe distance from your next lightning storm.