Hail Storms

Hail Storms

How Hail Forms

Within these thunderstorms, very fast currents of air move upwards (called updrafts) and downwards (called downdrafts). Inside the updrafts, water vapor (which is a gas) and rain (which is liquid) are pushed extremely high into the cumulonimbus cloud. At a certain height, the air temperature drops below freezing, and the water condenses onto dust or other such particles, known as condensation nuclei. The supercooled water molecules condense onto the condensation nucleus and freeze, producing a tiny ice particle which serves as the center of the hailstone.

World's Largest Hailstone: Vivian, Nebraska

Image of the world's largest hailstone that fell on July 23, 2010 in Vivian, South Dakota. (Photo: NWS)  (NWS Aberdeen, South Dakota)

Through time, the tiny ice particle will remain lofted within the thunderstorm due to the force of the updrafts, but it will fall below the freezing line due to the force of gravity. As it does so, the ice particle collides with rain drops and other ice particles and accumulates a layer of water, or aggregates together into an icy, spiky clump. It eventually gets caught in an updraft and is forced above the freezing layer, causing this new layer to freeze.

The hailstone then undergoes the up-and-down cycle within the thunderstorm until one of two situations: the hailstone encounters a downdraft that sends the hail to the ground, or the hailstone grows to a size in which it is too large for the storm's updrafts to overcome the force of gravity, at which it falls to the ground.

According to the National Weather Service, in order for a thunderstorm to produce dime-sized hail, its updraft speed