Science: Inside Thunderclouds

Thunderclouds—and the plane-racking turbulence that goes on inside them—are a constant menace to a pilot. He cannot always tell whether the cloud ahead is dangerous or not. Last week both the airlines and the U.S. Weather Bureau were peering into clouds with radar—which seems to be the way to spot a genuine thunderhead full of dreaded turbulence.

What a radar "sees" is not the thundercloud itself; raindrops or hailstones inside it reflect the radar's waves. The fierce air currents do not show up on the scope, but the presence of large masses of raindrops is a strong indication of turbulence. A plane...