This is a fair question – it’s been terribly hot every day this week, with massive thunderstorms every evening. Here’s what causes this phenomenon:
Hot weather increases the rate of evaporation of surface water. We all know that hot air rises. As the air moves upwards, into the atmosphere, laden with water, it begins to cool because the temperature up there is cooler than the temperature on the land. Clouds form. Warm air can hold more water than cool air. When the air temperature drops, the air becomes saturated with water and it rains. As the droplets of water fall through the clouds, they pick up negative charges and here is where my knowledge of physics starts and ends. Something happens between negative and positive charges, and suddenly we’ve got a thunderstorm on our hands.