What Creates a Shelf Cloud

Did you see these cool clouds in our area this morning? We saw similar pictures flow in last weekend, too, as storms raced through our area. These are shelf clouds, which can look pretty ominous when they show up above your neighborhood. These are usually the clouds that invoke references to Independence Day (the movie) or alien spaceships.

A shelf cloud shows up on the leading edge of a line of strong storms. When you see a setup like this, expect the wind to get strong when the cloud formation gets closer to you. You are also likely in for some heavy rain and lightning, so head indoors after snapping a pic from a safe distance.

Another easy way to identify a shelf cloud is that it takes up most of the horizon; it's not a small cloud feature. Think of these has having a horizontal (as opposed to vertical) axis, like a roll of carpet. You may even notice a shelf cloud rotating in the horizontal plane but not usually in the vertical.

These types of clouds form when the downdraft in a thunderstorm brings cooler air down with it. That cooler air displaces warmer air out ahead of the storm, lifting the warmer air up which causes it to condense. When the rising warm air condenses, it forms the shelf cloud you see advancing toward you ahead of the thunderstorm. To keep this going, the storm needs to maintain a pretty strong downdraft of cool air in an environment with lots of warm air ahead of it. This is also why you likely notice a temperature drop as the shelf cloud passes you, in addition to the rain and wind already mentioned.

To be a shelf cloud, the feature must stay connected to the storm. If the cloud becomes disconnected from the storm and is way out ahead of it, that's a roll cloud. They look similar but a roll cloud isn't connected to the thunderstorm itself. You also don't want to confuse a shelf cloud with a wall cloud; they are different, but we won't dive into wall clouds here to avoid confusion. Share your cloud pictures with us on social media; we love to see what the view looks like where you are!