CENTRAL ILLINOIS (WCIA) – Stunning images were captured over parts of Central Illinois Monday evening and again Tuesday morning.

The cloud formations were associated with towering cumulonimbus thunderstorms reaching high into the sky. These storms were as high as 50,000 to 60,000 feet tall at times, and they could be spotted in some cases over 200 miles away.

As the towering updrafts continue to rapidly grow, they eventually reach the top of the lowest layer of the atmosphere (stratosphere), and then hit a stable layer of air called the tropopause. This is the boundary that sits between the troposphere (layer closest to the surface) and the stratosphere (the next layer of the atmosphere).

These updrafts can sometimes punch through the tropopause if there is enough rising motion (overshooting top), but more than anything the tropopause acts as a ceiling, and rising air then spreads out like a pancake along it. This spreading of the air is called an anvil, and can often be seen for miles and miles, spreading 10s of miles away from the parent thunderstorm, often in the direction of the jet stream overhead.

Photo courtesy NOAA National Severe Storm Laboratory

It is under the anvil of these powerful thunderstorms that Mammatus clouds are most common in Central Illinois, much like they were last night and this morning. As the anvil spreads and the air cools, pockets of air begin to descend from the anvil, forming what looks like bubbles under the bottom of the anvil.

These pouch like structures can be rather common, but are not always as noticeable as they were this week. Sometimes they can vary from small and barely recognizable to large and well defined pouches.

Often, Mammatus clouds are thought to be associated with tornadoes, as supercell thunderstorms that produce tornadoes are strong enough to also produce these. Most tornadic storms do produce these clouds, but they are also common on general thunderstorms and even sometimes on simple showers during the changing of the season. Even in the winter time, when conditions are right they can occur when there are snow showers in the area.

Next time you see clouds like these, you’ll know what they are and why they form. While not always associated with severe storms, it’s still more common to see them associated with them in Central Illinois.