This morning some ominous looking clouds rushed over Kentucky, and apparently, much of the Eastern US as well. According to the meteorologists, these are shelf clouds. Shelf clouds often resemble snow plows, big waves or tsunamis and can be very scary-looking since they are usually low-hanging. Sometimes they may found only a couple hundred feet above the ground.
A shelf cloud is a low, horizontal wedge-shaped cloud, associated with a thunderstorm gust front (or occasionally with a cold front, even in the absence of thunderstorms). A rising cloud motion often can be seen in the leading part of the shelf cloud, while the underside often appears turbulent, boiling, and wind-torn. The weather radar this morning showed large areas of rain and thunderstorms in Indiana.
There are two other phenomena that might resemble tornadoes or funnel clouds but are not 1) dark rain shafts or narrow columns of heavy rain, and 2) the white color of a hail shaft, a column of hail extending from the ground to the cloud base, may generate a light-dark contrast with surrounding rain, resulting in what might appear to be a funnel cloud or a tornado to the untrained eye. “A shelf cloud is the boundary between a downdraft and updraft of a thunderstorm or line of thunderstorms,” says weather.com senior meteorologist Jon Erdman.
“Rain-chilled air descends in a thunderstorm, 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. As the shelf cloud passes, you feel an abrupt wind shift in both direction and speed, followed within minutes by heavy rain or hail. Wind gusts once the shelf cloud has passed may be quite strong, causing downed trees, tree limbs and power outages.” As the cloud approached, the wind blew strongly, and the temperature seemed to drop. Although it looked like we were going to get a real downpour, the rain stayed north of the river.