Why can one hailstone have both clear and cloudy ice layers instead of growing in one simple up-and-down path?

Answer: It moves through storm zones with different freezing speeds

Lightning flashes mark the ice as it grows — Lightning can accompany hailstorms, so it is an easy thing to picture. But it does not paint layers inside the stone. The clear-or-cloudy pattern comes from how newly collected water freezes around the hailstone and whether tiny air bubbles get trapped.

Each band comes from a separate thunderstorm — A hailstone can record changing conditions, but those changes do not require a new storm for every band. Strong storms have complicated sideways and rotating winds inside one cloud system. A single stone can travel through several growth zones before it finally falls.

It moves through storm zones with different freezing speeds ✓ — The layers are a record of changing growth conditions. When water freezes more slowly, bubbles can escape and the ice looks clearer; when it freezes quickly, bubbles get trapped and the ice looks cloudy. Because the stone's path through a storm is three-dimensional, not just a vertical elevator ride, it can collect alternating layers.