What is a shelf cloud?

By  | 

BRIDGEPORT, W. Va. (WDTV) - Have you ever seen a low-hanging, wedge shaped cloud? That is a Arcus cloud called a shelf cloud.

This is a low, horizontal formation that occurs along the leading edge of a gust front in a thunderstorm.

A shelf cloud itself is harmless but indicates a potentially dangerous storm.

Thunderstorms are formed by downdrafts and updrafts. Warm, unstable rises into a storm and fuels it. This is known as the "updraft."
As the rain falls, it cools the air and that air then sinks to the ground. This is called the "downdraft."

All the cool, air from the downdraft pools beneath the storm. As that "cool pool" begins to race away from the storm, that is known as the outflow boundary or gust front.

The updraft then rises along the outflow boundary. As it does, it cools and condenses into a shelf cloud.

So if you see a shelf cloud like this, be sure to get inside before the storm hits.