When do shelf clouds form?

Shelf cloud?

Like this one in Austria, they can look downright scary — but shelf clouds are actually a common thunderstorm feature, often signaling the arrival of strong, gusty winds.

They form when rain-cooled air inside a thunderstorm sinks, then surges outward and ahead of the storm. That cooler, denser air wedges underneath the warmer, more humid air ahead of it, forcing that air upward.

As it rises, it cools and condenses, forming that long, dramatic ledge of cloud along the storm's leading edge.

The cloud itself isn't the danger — but the gust front beneath it can be your signal to get inside.

And storm chasers have naturally found the perfect name for pictures taken in front of them.

You guessed it:

#Shelfie.