Lowering of a cloud base at low levels in a thunderstorm.

A localized, persistent, often abrupt lowering from the base of a parent cloud. Wall clouds can range from a fraction of a mile up to nearly five miles in diameter, and normally are found on the south or southwest (inflow) side of the thunderstorm. When seen from within several miles, many wall clouds exhibit rapid upward motion and cyclonic rotation.

An area of clouds that extends beneath a severe thunderstorm. If a wall cloud rotates, it might precede tornado development.

A local and often abrupt lowering of a thunderstorm base into a low-hanging accessory cloud. Diameter is usually 1 to 4 miles. Rotating wall clouds usually precede tornado development.

A local, abrupt lowering of a rain-free cumulonimbus base forming a low hanging accessory cloud that is usually 1 to 4 miles in diameter. The wall cloud is usually situated in the right-rear quadrant of the cumulonimbus with respect to storm motion, below an intense updraft associated with a strong or severe thunderstorm. Rotating wall clouds often precede tornado development.

An isolated lowering of a cloud that is attached to the rain-free base of a thunderstorm, generally to the rear of the visible precipitation area. Wall clouds indicate the updraft of or the inflow to a thunderstorm.

The region of deep cloud surrounding a mature cyclone eye.

A local, often abrupt lowering from the rain-free base of a thunderstorm. Wall clouds can range from a fraction of a mile up to nearly 5 miles in diameter, and normally are found on the south or southwest side of the thunderstorm. When seen from within several miles, many wall clouds exhibit rapid upward motion and counterclockwise rotation. Rotating wall clouds usually develop before strong or violent tornadoes, by anywhere from a few minutes up to nearly an hour. Wall clouds must be monitored visually for signs of persistent, sustained rotation.

a generally rain-free region of rotating clouds which extends beneath a severe thunderstorm and from which a funnel cloud may form

(Sometimes referred to as pedestal cloud.) A local, often abrupt lowering from a cumulonimbus cloud base into a low-hanging accessory cloud, normally a kilometer or more in diameter. A wall cloud marks the lower portion of a very strong updraft, usually associated with a supercell or severe multicell storm. It typically develops near the precipitation region of the cumulonimbus. Wall clouds that exhibit significant rotation and vertical motions often precede tornado formation by a few minutes to an hour. Fujita, T., 1959: A detailed analysis of the Fargo tornadoes of June 20, 1957. U.S. Wea. Bur. Res. Paper 42, p.15.

Subject: The Earth An area of rotating clouds that extends beneath a severe thunderstorm and from which a funnel cloud may appear. Also called a collar cloud.[ Pics List

An abrupt lowering of a cloud from its parent cloud base, a cumulonimbus or supercell, with no visible precipitation underneath. Forming in the area of a thunderstorm updraft, or inflow area, it exhibits rapid upward movement and cyclonic rotation. It often develops before strong or violent tornadoes.

A wall cloud is a cloud formation. It is a lowering beneath the rain-free portion of a thunderstorm, and indicates the area of maximum updraft. In the special case of a supercell thunderstorm, the wall cloud will often be seen to be rotating.