LOTS of great photos!!
Lymerick
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A shelf cloud, also known as an arcus or arc cloud, may be the most frequently submitted cloud photo to our weather.com photo gallery and Facebook page. Based on their appearance, we certainly understand why.

A more rare variety of this type of cloud, a roll cloud, resembles a giant rolling pin in the sky. The first two photos in the slideshow from Lake Hendricks, Minnesota, on June 20, 2015, show a terrific example of a roll cloud.

To understand how roll clouds form, we first must explain how shelf clouds develop.

Shelf clouds are typically seen at the leading edge of a thunderstorm or squall line of thunderstorms. While menacing in appearance, shelf clouds are not tornadoes or wall clouds.

(PHOTOS: Scary Clouds That Are Not Tornadoes)

What you're seeing in a shelf cloud is the boundary between a downdraft and updraft of a thunderstorm or line of thunderstorms.

Rain-chilled air descends in a thunderstorm's downdraft, then spreads laterally when reaching Earth's surface. Warmer, more moist air is lifted at the leading edge, or gust front, of this rain-cooled air. When this warm, moist air condenses, you see the shelf cloud.

SNIP