Sleet forms in winter storms, while hail is a warm-season type of precipitation. As noted above, sleet forms when snow melts in a warm layer and then refreezes into ice pellets as it falls though a cold layer. Hail, however, forms in spring, summer or fall thunderstorms.
Explanation:
I put this question before and got this one so I think it will be this answer. Hope this helps. :)
