Thunderstorms are a type of weather formation. The light level falls to 10, but mobs spawn as if the light level was 5. Lightning may strike during thunderstorms, but the resulting fire is usually put out by rain. Thunderstorms can occur in deserts, where there is no rain to stop a fire. However, most of the time the lightning will not strike in them, and there is nothing to burn. Thunderstorms are dangerous, as they may occur at any time with little warning. Zombie Pigmen may spawn as well, as Pigs struck by lightning mutate. Charged Creepers present another hazard, but both of these transformative occurences are very, very rare. Rain falls anywhere it can normally.