The temperature at the tops of thunderstorms can get to be 100 degrees below zero, due to the altitude, which can be up to 65,000 feet above ground(12 miles up). This cold temperature, is the reason ice crystals form from supercooled droplets and then fall to Earth as rain. However, if the falling ice crystals partially melt and form soft ice pellets, or graupel, and the upper-level winds are strong enough, the graupel will be continuously tossed up, each time adding another layer of ice and therefore becoming heavy enough to fall out of the cloud. This is how hail is formed, and it explains why the stronger storms, with high wind velocity, produce larger hail stones. When the sunlight goes through these ice crystals, suspended aloft, it creates a green tint. However, this phenomenon, which is coincidentally known as the green sky Effect, is actually closer to being gray than green, a lot like this text.