Accessory cloud Accessory cloud An accessory cloud is a cloud which is dependent on a larger cloud system for its development and continuance. It is often an appendage but also can be adjacent to the parent cloud system. The arcus and roll clouds, shelf cloud, wall cloud, and scud are examples of low level or vertical accessory clouds whilst the anvil, and overshooting top, are examples of high level accessory clouds. The condensation funnel of funnel clouds and tornadoes are also accessory clouds. They are associated with deep moist convection and especially cumulonimbus, the primary cloud producing thunderstorms. The pileus and mammatus
Cloud seeding is used to increase precipitation in areas experiencing drought, to reduce the size of hailstones that form in thunderstorms, and to reduce the amount of fog in and around airports. In the summer of 1948, the usually humid city of Alexandria, Louisiana, under Mayor Carl B. Close, seeded a cloud with dry ice at the municipal airport during a drought; quickly 0.85 inches of rainfall occurred. Cloud seeding is occasionally used by major ski resorts to induce snowfall. Eleven western states and one Canadian province (Alberta) have ongoing weather modification operational programs. In January 2006, an $8.8 million cloud seeding