Explain why some storms produce huge hailstones.

Powerful updrafts in thunderstorms

In a heavy storm, the warm air at the ground is sucked upwards at sometimes impressive speeds. This vertical current, called updraft, can easily exceed 100 km/h. The stronger this current, the farther it carries small water droplets upwards, transporting them to the icy regions of the clouds. Once up there, this mixture cools quickly, freezing into small solid pieces. When these pieces attempt to fall, the enormous force of the updraft immediately lifts them back up. Trapped inside, these small hailstones gradually grow, accumulating layer after layer of ice, until they sometimes become truly enormous. The more intense the updraft, the larger the hailstone created.

The extended duration of vertical circulation

In some heavy storms, hailstones spend their time going up and down. They continuously rise and fall within the cloud thanks to very strong air currents that last a long time. The longer this vertical ride lasts, the more chance the hailstone has to accumulate additional layers of ice. The result: instead of just having a small hailstone, you end up with a real large projectile. Persistent vertical circulation allows these ice blocks to gain size and weight before finally falling to the ground.

Very cold temperatures at high altitudes.

At high altitudes, the extremely cold air plays a crucial role in forming huge hailstones during thunderstorms. This very cold zone allows water droplets that rise with the updrafts to freeze quickly. The colder it is at the top, the faster and easier the water freezes, forming solid hailstones with different layers of ice. Each pass through this icy region adds a new layer, making these pieces of ice grow larger and larger. When these hailstones become too heavy to be supported by the updraft, they then fall abruptly to the ground as huge hailstones capable of causing significant damage.

Humidity and initial size of water droplets

The more humid the air is, the more numerous and larger the initial droplets become. This really helps hail to grow quickly, as these large droplets will easily clump together and quickly form large hailstones. The less moisture the air contains, the harder it will be for the ice crystals to find partners to merge with, so the hail remains small. It's somewhat like when you want to make big snowballs: the wetter the snow, the faster it sticks, and the quicker your snowball grows.

Abundant presence of freezing nuclei

In storms, freezing nuclei act as seeds for ice. They are generally tiny particles like dust, pollen, or grains of sand carried aloft. The more there are, the more the small supercooled water droplets (very cold but still liquid) can quickly transform into ice. These particles provide an ideal surface for water to crystallize, thus facilitating the initial formation of hailstones. When there are many, hailstones form faster and can become much larger, as they have a solid base to rapidly accumulate more ice.