![]() ![]() Unlike a shelf cloud, the roll cloud is detached from its parent thunderstorm(s). Wind gusts once the shelf cloud has passed may be quite strong, causing downed trees, tree limbs and power outages. When this warm, moist air condenses, you see the shelf cloud.Īs the shelf cloud passes, you feel an abrupt shift in wind direction and increased wind speed, followed within minutes by heavy rain or hail. Warmer, more moist air is lifted at the leading edge, or gust front, of this rain-cooled air. Rain-chilled air descends in a thunderstorm's downdraft, then spreads laterally when reaching Earth's surface. What you're seeing in a shelf cloud is the boundary between a downdraft and updraft of a thunderstorm or line of thunderstorms. ( PHOTOS: Scary Clouds That Are Not Tornadoes) While menacing in appearance, shelf clouds are not tornadoes or wall clouds. Shelf clouds are typically seen at the leading edge of a thunderstorm or squall line of thunderstorms. To understand how roll clouds form, we first must explain how shelf clouds develop. ![]() The first two photos in the slideshow from Lake Hendricks, Minnesota, on June 20, 2015, show a terrific example of a roll cloud. Based on their appearance, we certainly understand why.Ī more rare variety of this type of cloud, a roll cloud, resembles a giant rolling pin in the sky. An extreme example of this phenomenon looks almost like a tornado and is known as a gustnado.A shelf cloud, also known as an arcus or arc cloud, may be the most frequently submitted cloud photo to our photo gallery and Facebook page. A very low shelf cloud accompanied by these signs is the best indicator that a potentially violent wind squall is approaching. ![]() In a severe case there will be vortices along the edge, with twisting masses of scud that may reach to the ground or be accompanied by rising dust. A shelf cloud usually appears on the leading edge of a storm, and a wall cloud will usually be at the rear of the storm.Ī sharp, strong gust front will cause the lowest part of the leading edge of a shelf cloud to be ragged and lined with rising fractus clouds. This is likely a mistake, since an approaching shelf cloud appears to form a wall made of cloud. People seeing a shelf cloud may believe they have seen a wall cloud. As the lower cooler air lifts the warm moist air, its water condenses, creating a cloud which often rolls with the different winds above and below ( wind shear). This outflow cuts under warm air being drawn into the storm’s updraft. Cool, sinking air from a storm cloud‘s downdraft spreads out across the land surface, with the leading edge called a gust front. Rising cloud motion often can be seen in the leading (outer) part of the shelf cloud, while the underside often appears turbulent and wind-torn. A shelf cloud is attached to the base of the parent cloud, which is usually a thunderstorm cumulonimbus, but could form on any type of convective clouds. Ī shelf cloud is a low, horizontal, wedge-shaped arcus cloud. Saturn, Jupiter, the Moon, stars and constellations – and the rest of the Michigan’s sky will be completely hidden behind an unrelenting cover of clouds – seemingly for eternity. ![]() During the ride, he complained that Michigan’s continually overcast skies looked like the skies of Mordor I can’t stop myself from using that trope. Many years ago, I picked up my brother from Detroit Metro Airport and drove him to Flint. I go to a lot of science fiction conventions, and drag my telescopes with me I frequently get blamed for bringing the clouds with me… School children in Michigan are taught that there are these mysterious things beyond the clouds but the Sun, Moon, planets and stars are elusive to those who live under the “Michigan nebula.” This last weekend, a Girl Scout troop was scheduled to do some viewing at the Warren Astronomical Society’s Stargate Observatory outreach volunteers had to give presentations inside one of the camp buildings because of cloud cover and cold there was even a light covering of snow on the ground the next morning… ![]()
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