Hailstones are a form of precipitation which are basically ice balls by the time they reach the ground. The ice forms as the water vapor in the clouds gets too heavy to float on air, and while it travels to earth, it passes through freezing temperatures. The air temperature may be in layers where the precipitation melts and then freezes between layers. This causes the hailstone to grow larger the nearer it gets to the ground. The officially recognized biggest hailstone fell near Vivian, South Dakota on July 23, 2010.