When they develop they do not move as a system but continuous development occurs on the windward side and the dissipation occurs at the downwind region. Roll clouds and shelf clouds Roll and shelf clouds are clouds mostly associated with the front bases of some thunderstorms. When updraughts of warm moist air are adjacent to downdraughts consisting of cold air, condensation occurs. The difference between shelf and roll clouds are that roll clouds involve horizontal rotations. These always display continuous changes.
Roll clouds can also develop in the absence of thunderstorms.
Sometimes, rapidly approaching cold fronts produce roll clouds under similar conditions. They most commonly occur below bases of thunderstorms although some occur with wind changes such as cold fronts. Scud clouds go through continuous rapid changes. They give some indication of approximate air flow into the cloud bases. Back to top Microbursts Microbursts are downdraughts that accelerate to the surface from the clouds.