Those are called mammatus clouds

WTWO-TV 2 Chief Meteorologist Jesse Walker was inundated with questions Monday night — calls to the station, scores of social-media queries — asking not about impending threatening weather, but about the clouds floating peacefully in the sky.

Mammatus clouds resemble large pillowy cotton balls, but are associated with severe storms and traditionally don't last very long in the sky, perhaps 15 minutes or so.

"But we had big storms to the southwest of us [Monday evening], and those storms stuck around, so these [clouds] lasted for hours, which is very unusual," Walker explained. "They lasted for a long time, so many people got to see them."

Most clouds are formed by rising air, but mammatus clouds are formed by sinking air, which by nature is colder air, so mammatus clouds are usually filled with ice.

Walker said someone recently asked him what his favorite type of cloud was, and after some reflection, he answered mammatus clouds.

"They're kind of rare, and very unusual," he said.

"Crazy" was how Walker described the response from viewers regarding Monday's clouds. "It was definitely the talk of the station last night," he said.

Walker provided his followers with a link to a Twitter page responding to the hashtag #mammatusclouds, featuring photos and videos of that particular variety of cloud from all over the country.

David Kronke can be reached at 812-231-4232 or at david.kronke@tribstar.com.