How do hail pellets get bigger?

Hail pellets get bigger through a process called accretion, where supercooled water droplets in a thunderstorm freeze onto a hailstone as it is lifted and falls through the storm multiple times. The hailstone grows as more water freezes onto it, creating layers of ice. The stronger the updrafts in the storm, the more times the hailstone is lifted and falls through the storm, allowing it to accumulate more ice and grow in size.