Tornadoes are mysterious. But on this EarthDate, we’ll try to unravel a few of their secrets.

You’ve probably heard there’s a “tornado season” that happens in “tornado alley.” Well, not exactly.

Tornadoes can happen almost anywhere—North and South America, Australia and New Zealand, South Africa, and the Indian subcontinent, where they’re most deadly due to higher population density.

And they can happen any time. Most occur within a few months…but that depends on where you are. In the southeastern US, it’s January through March. In the central plains, April through June. In the Midwest, July through September. The only months they’re less frequent are October through December.

Tornadoes appear to form from the cloud downward. But that’s not really the case. Researchers think most of them form horizontally, within the cloud, like a rolling barrel. Then an updraft turns them vertical, and they extend to the ground…

Or not. Some scientists think they may form from the bottom up, as a swirling wind eddy on the ground reaches up to the cloud, connecting to and triggering that rolling barrel of wind. Or it could be some of each.

But we can’t really tell by looking at radar since tornadoes form too quickly and too near the ground for our current technology to map them.

Clearly, there’s still a lot of mystery surrounding tornadoes. But as research comes in, we’ll keep blowing it your way.