How big can hail get (and how is that even possible)?

You don't want to play golf with this, nor do you want it falling on your car.
You don't want to play golf with this, nor do you want it falling on your car.

Say you don't live in the tropics, or even in a nicely temperate zone where your garden can reliably sprout tomatoes during a lengthy growing season. Say instead you must eke out fresh produce during a severely truncated summer in a northern location like, for instance, Alberta. The answer to your problem, of course, is a greenhouse. So, you invest a few thousand dollars in an aluminum-and-plastic structure, and before you know it, heirloom tomatoes are spiraling upward, flowering and fruiting and generally promising an abundant harvest.

Then comes July. High summer. One day, a tremendous thunderstorm passes over. Exciting! You love lightning. But then, white bullets fire down from the heavens. Golf balls made of ice. It's hail.

When you dare to go outside again, your windshield is shattered, your trees have been de-limbed, your beautiful new greenhouse is in tatters and the tomato plants inside it are corpses.

Did you forget that Alberta is in the so-called "Hail Alley"? Your insurance company didn't. If you heard a droning sound before the storm, that was a fleet of planes taking off and flying straight into the gathering thunderclouds. Their mission? To cut the hail down to size through a process called cloud seeding.

Back in 1991, a 30-minute hailstorm caused so much damage in the city of Calgary that insurers ended up forking over $342 million to their customers. Loathe to make a payout like that again, they banded together and hired a North Dakota outfit to do something about it. Weather Modification Inc. (WMI) flies cloud-seeding planes above and below hail-producing clouds, while firing flares full of silver iodide in the hopes of reducing the size of the hailstones [source: Sheremata].

How that works, or at least how they hope it works, gets us closer to the answer we seek. Just how big can hail get?