Little white pieces of ice are falling from the sky. Is it hail or sleet? Size isn’t the only factor. The critical difference is layers. Sleet is formed by a frozen raindrop, or a refrozen melted snowflake, resulting in a solid sphere of ice. Hail, on the other hand, typically consist of layers of ice that form as core of the hailstone passes through various layers of the thunderstorm. Hail can get quite large. In 2003, Nebraska recorded the largest hailstone in the US, when a hailstone with a 7-inch diameter fell in Aurora. This beat the previous record stone from Coffeyville, KS which had a diameter of 5.7 inches and a circumference of 17.5 inches. Then on July 23rd, 2010 Vivian South Dakota saw a mammoth snow with an 8-inch diameter. The Aurora stone still holds the record for circumference.
Mary Knapp, Weather Data Library