1.   Hail is unusual in San Diego, given the lack of thunderstorms with updrafts that are sufficiently strong to suspend embryonic hailstones long enough for them to grow.

2.   Here, embryonic hailstones grow while suspended by updrafts.

3.   Once frozen, the embryonic hailstones grew as they collided with billions of tiny cloud drops that froze on contact.

4.   Tiny water drops high in a cloud freeze onto the silver iodide, forming embryonic hailstones.

5.   Within thunderstorms, updrafts of air must be sufficiently strong for embryonic hailstones to grow.