Hail forms inside strong thunderstorms with powerful updrafts that carry raindrops upward into very cold regions of the atmosphere. Here is a detailed explanation of the process:
- Raindrops are lifted by the storm's updrafts high into the cloud where temperatures are below freezing. At this altitude, the droplets freeze and form small ice pellets or hailstones
- These hailstones grow larger as they collide with supercooled water droplets (liquid water below freezing temperature) that freeze upon contact. This process can happen repeatedly as the hailstone is carried up and down within the storm by updrafts and downdrafts, accumulating layers of ice
- The hailstone's layers can be clear or cloudy depending on how quickly the water freezes. Slow freezing allows air bubbles to escape, creating clear ice, while rapid freezing traps air bubbles, resulting in cloudy ice
- Eventually, the hailstone becomes too heavy for the updraft to support, or the updraft weakens, causing the hailstone to fall to the ground as solid ice
- The size of hailstones depends on the strength and duration of the updrafts. Stronger and longer-lasting updrafts allow hailstones to grow larger by repeatedly cycling through freezing layers in the cloud
In summary, hail is made by thunderstorm updrafts lifting water droplets into freezing heights where they freeze and grow by collecting more supercooled water, until they become heavy enough to fall as ice balls or lumps to the surface
