jimbaerselman
New member
Roll cloud, often spinning around a horizontal axis. Often associated with strong, fast moving cold fronts.
Above the far side of the cloud is a massive updraft sucking wind in from both sides. The near side is a strong downdraft (shown by the mammatus clouds) hitting the ground then blowing under the cloud to feed the updraft.
The roll is a vortex caused by the updraft next door to the downdraft. It's whizzing around so fast that the pressure is lowered inside the vortex, dropping the temperature just below dew point. Similar cause creates the water vapour tubes in "waterspouts".
