Weird Clouds: Mammatus

Mammatus clouds over Pittsburgh, 16 June 2022, 9:00pm (photo by Kate St. John)

17 June 2022

Severe thunderstorms were predicted for 6:00pm yesterday in the upper Ohio Valley. By 2:00pm the Severe Thunderstorm Watch called for an inch of rain in 1 hour — definitely flash flood material — but at 5:00pm the storm line split. Some went north toward I-80, the rest went south to West Virginia. Pittsburgh had no lightning, no strong winds, no rain. Nothing happened.

But the sky got weird. At sunset the last of the storm clouds left our area with a flourish of rare mammatus clouds, dramatically lit from below. Their name is derived from the Latin word for breast or udder.

As Wikipedia explains, mammatus are formations that hang from the base of rain clouds. The distinct lumpy undersides are formed by cold air sinking down to form pockets. Usually composed of ice, each lobe averages 1/2 to 2 miles across and 0.3 mile deep. Alone a lobe can last 10 minutes but a cluster may last several hours.

Mammatus are an indication of a severe thunderstorm but in my experience in Pittsburgh they do not predict the storm. Instead they show up after the storm has passed.

The clouds started out as lines and gave way to stratus clouds and a gleam at sunset.

Mammatus clouds forming lines, Pittsburgh PA, 8:58pm, 16 June 2022 (photo by Kate St. John)
Mammatus clouds looking east, Pittsburgh PA, 8:58pm, 16 June 2022 (photo by Kate St. John)
Last line of mammatus clouds gives way to stratus at sunset, looking west, Pittsburgh PA, 9:05pm, 16 June 2022 (photo by Kate St. John)

Next time you see these weird clouds, remember their name describes their shape.

p.s. Steve Tirone left a comment with a link to his video of the clouds.

(photos by Kate St. John)

7 thoughts on “Weird Clouds: Mammatus

  1. I saw them too, dramatically illuminated red by the setting sun. I had the same experience many years ago and have photos from back then. The only other time I saw these clouds was in Colorado a few years ago after a storm at the Pawnee Grasslands. An exciting rare weather phenomenon, although they are associated with severe storms so they can be concerning.

  2. Thanks, Kate for this post. I saw these strange looking clouds and never encountered them before. I was going to reach out to you to explain what they were. Mother Nature holds many phenomenon in store for us. We need to keep our eyes open.

  3. Walking to work one day– camera in hand– I happened to look up and noticed some unusually- shaped clouds the like of which I’d never seen before. I took a photo, later downloaded. I learned that they are called mammatus clouds. (And if I told you I wasn’t amused when I found out their name, I’d be lying: Because inside every grown man…
    is a 12-year old boy!)

    Wonderful photos/video. Another great article, Kate!

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