People watching the skies above Allegheny County and surrounding areas Thursday evening for signs of potential thunderstorms instead were treated to vistas of clouds resembling fluffy cotton balls.
Known as mammatus clouds, they are a rare example of clouds that form in sinking air instead of rising air, according to the website earthsky.org.
Tinted by the setting sun, they provided a visual treat and great photo opportunities for many in the area, including meteorologist Shannon Hefferan and her colleagues at the National Weather Service office in Moon.
The view from our office this evening!????
— NWS Pittsburgh (@NWSPittsburgh) June 17, 2022
Time lapse taken by @jaredrackley #MammatusClouds pic.twitter.com/dO0D11Ohzq
“They were pretty much everywhere for a good three hours,” Hefferan said of the clouds. “It was quite a show.
“We were sort of surprised to see them. They’re usually seen in the Plains states, but they do occasionally happen here.”
Did you take pictures?
• We'd love to see your images. Send them to us via a message on our Facebook pageThe mammatus cloud formation can be associated with severe weather, but that’s not always the case, Hefferan said.
While storms passed to the north and south of Allegheny County, she said, “There was no severe weather here at all.”
According to earthsky.org founder and science educator Deborah Byrd, mammatus clouds are pouch-like protrusions primarily composed of ice that extend from the underside of clouds. They can extend for hundreds of miles.
The clouds can be associated with severe weather, appearing in the vicinity of or before or after a storm, Byrd says, but she notes that it is a myth that the clouds can extend down to form tornadoes.
According to the Department of Atmospheric Sciences at the University of Illinois at Urbana-Champaign, the mammatus formation can occur with a high concentration of ice crystals and water droplets, resulting in saturated air that is heavier than the surrounding air and sinks toward the earth.
