First Warning Weather University: How Does Hail Form?

Austin

AUSTIN (KXAN) –  How does hail form? It starts with a thunderstorm.

Ever notice how thunderstorm clouds are much deeper and taller than other clouds? That’s because there’s a stronger current of rising air inside of the cloud called an “updraft”. This is the same thing that causes airplane turbulence.

This updraft carries little particles up into the cloud. As those particles rise through the cloud, they bump into tons of tiny water droplets. That original particle serves as something for the water droplets to stick to, which then grows into a rain drop.

As the particles rise, they reach an area where the air temperature drops below freezing. At this altitude, the rain drop turns into ice. This ice, which will end up being the very center of the hailstone, violently collides with “super cooled drops” of water that haven’t had a chance to freeze yet. When these collide, they freeze, and the hailstone grows.

This process continues until the hailstone gets too heavy and falls to the ground.

If the wind blowing straight up through the cloud towards space is only 25 mph, the hail will fall when it reaches the size of a pea. If the updraft speed is 50 mph, the hail falls when it reaches the size of a quarter. Quarter-sized hail is fairly common in Central Texas.

If the storm is strong enough to have an updraft of 100 mph, the hail might not fall until it’s as big as a grapefruit!

Hailstones can fall very fast. That’s why hail is really dangerous to be outside in and can be a big threat to pets and livestock.

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