News Columns & Blogs

How hail happens

In a blogpost about the Wingnuts game at Lawrence Dumont Stadium Wednesday night, Eagle colleague Jeff Lutz added this:

The thing I can't figure out, though — and it's kind of a "speaking the obvious" thing. But why is hail cold? I get that it's ice. But it was 85 degrees last night. What's going on up in the sky to not only turn water to ice in midair, but also make it cold? I'm sure it has something to do with atmospheric pressure or something like that, but it's one of those things that seems obvious yet no layperson really has an answer for.

Actually, Jeff, there is an answer. Hail is cold because it’s ice. Hail is ice because it forms in layers of the atmosphere where the temperature is below freezing. As the ice crystals are buffeted around in the upper levels of the thunderstorm, they gradually accumulate moisture that also freezes, making the stone larger.

The stones fall toward the earth, but if the updrafts in the storm are strong enough they’ll push the stones back up into the upper levels again, where the process repeats itself: moisture attaches itself to the stone and freezes, making it even larger.

Eventually, the stones become too heavy to be kept aloft, and they fall to the ground. The larger the hail stones, the stronger the updrafts aloft in the thunderstorm.

That’s why large hail is one marker of an impending tornado: the same updrafts that make the large hail possible can be an ingredient in the formation of a tornado - though not every thunderstorm that produces hail is capable of developing a tornado, and not every tornadic thunderstorm has hail in it.

The temperatures near the surface of the ground - where we are - have no real bearing on the formation of hail. They merely have a say on how quickly the stones melt.

  Comments