We had a spectacular show Friday night as the second round of storms for the day passed by to the east. A nice field of mammatus clouds developed.
I went out anticipating that the thunderheads to the east might have some interesting illumination from the setting sun to the west, but was very pleased to see these clouds and watch as the grew and developed.
The following bit of information is condensed from Wikipedia: Mammatus are most often associated with the anvil cloud that extends from a cumulonimbus (thunderheads). Mammatus are often indicative of a particularly strong storm or maybe even a tornadic storm. These tend to form more often during warm months and are most common over the midwest and eastern portions of the United States.
Mammatus may appear as smooth, ragged or lumpy lobes and may be opaque or semitransparent. Because mammatus occur as a grouping of lobes, the way they clump together can vary from an isolated cluster to a field of mamma that spread over hundreds of kilometers to being organized along a line, and may be composed of unequal or similarly-sized lobes. The individual mammatus lobe average diameters of 1–3 km and lengths on average of 0.5 km. A lobe can last an average of 10 minutes, but a whole cluster of mamma can range from 15 minutes to a few hours. They usually are composed of ice, but also can be a mixture of ice and liquid water.
As the sun sank lower, the clouds turned from yellow to red.
It was rather exhilarating to be outside walking under this strange meteorologic phenomenon under a wide open sky!