A supercell thunderstorm looms east of Leedey, Okla., on April 22, 2013. (Photo courtesy of Roger Hill)
They look like an alien invasion, but rotating supercells happen far more often than a visit from E.T.
The photos above are examples of what happens when forces of weather combine to produce an incredibly photogenic sight -- known simply as the "mothership" cloud.
Captured by storm chasers and weather-gawkers, these approaching storms were already ominous. However, with the rise of photo-enhancement apps like Instagram, which allow amateurs to make images appear professionally edited, rotating supercells look more like alien spacecraft than ever.
The Science Behind Supercells
From Nick Wiltgen, weather.com meteorologist in an April 2013 article:
"A supercell thunderstorm is characterized by a sustained and powerful rotating updraft. These storms originate in unstable air accompanied by a particular type of changing wind direction at various altitudes in the atmosphere; a common combination supportive of supercells is a southerly or southeasterly wind near ground level and a southwesterly or westerly wind higher up in the atmosphere.
This combination of changing wind directions creates a horizontal rolling motion in the lower atmosphere. The same rapidly rising air motions that form the thunderstorm turn this horizontal rotation into a vertical rotation, and in the case of this particular storm, this rotation is spectacularly evident in the circular striations, or layers, visible in the cloud structure.
The structure of supercell thunderstorms allows rain and hail to fall well away from the source of the warm, unstable air fueling the storm, so these storms do not choke on their own rain-cooled air. In some cases this allows supercell thunderstorms to stay intact for hours, covering tens or even hundreds of miles. In the process they can produce giant hail, very high winds, and tornadoes."
If you have photos of "mothership" clouds, we hope you'll submit them to our iWitness Weather page.