10 Amazing Rare Cloud Formations in Images - Listverse
Shelf Cloud Unlike roll clouds, shelf clouds are attached to a larger parent cloud. But, like the roll cloud it, too, is an arcus cloud. They are often enormous and frequently forewarn the coming of a big storm, whereas roll clouds typically do not precede bad weather. Shelf clouds can falsely give the appearance of being a wall cloud (which comes after a storm) but a shelf cloud usually has a ragged bottom.