Hail is a form of precipitation that consists of hard spheres of ice that range from 0.2 to 6 inches in diameter. Snow is water that has crystallized in the atmosphere before falling.
There are seven types of snow crystals, which are all distinct from the three forms of particle precipitation, which include graupel, hail and sleet. Hail usually forms when convective clouds with strong updrafts are present. As a result, hail often occurs alongside thunderstorms. The ice pellets that characterize sleet often resemble hailstones, but they are of a smaller size, usually less than 0.2 inches in diameter.
The ice crystals that are characteristic of snow do not form directly from water vapor unless the temperature is below minus 40 degrees Celsius. At temperatures above minus 40 degrees Celsius, snow crystals develop around very small dust or chemical particles floating in the air.