Hail is a warm weather phenomena. You get it in the summer, not the winter. What happens is that it's warm at low altitudes, but cold at high ones. Wind turbulence at high altitudes, which is an affect of the temperature differential, has ice crystals circulating up and down and combining with other moisture and growing into ever larger chunks of ice until it becomes hail and is too heavy for the winds to support any longer. Then it falls to the ground. It falls fast enough so that the warmer lower air doesn't melt it before it hits the ground.