What atmospheric condition is necessary for the formation of hailstones?

The formation of hailstones is predominantly associated with strong updrafts in cumulonimbus clouds. These powerful updrafts are critical because they carry water droplets high into the colder regions of the atmosphere, where temperatures are below freezing. As the droplets are lifted, they may freeze upon contact with ice nuclei. The updrafts ensure that these frozen particles continue to circulate within the cloud, allowing additional water droplets to accumulate and freeze onto the hailstone. This process can repeat multiple times, causing the hailstones to grow larger as they ascend and descend within the cloud until they become too heavy for the updrafts to support them, resulting in their fall to the ground.

Other atmospheric conditions, while they may contribute to storm formation, do not directly lead to hailstone development. For instance, stable atmospheric pressure or low temperatures alone are not sufficient to facilitate the complex dynamics of hail formation, and high humidity levels, while important for overall storm development, do not specifically point to the necessary conditions for hailstone creation. Strong updrafts are distinctly crucial for the growth of hailstones in a thunderstorm environment.