Surely all, sometime in our life, we have seen these clouds and we accompanied with a phrase of “petite storm will fall.”
These clouds, called clouds roll or, for those who know, arc clouds are created when an area of cold air comes into direct contact with hot air condensing the water present in the air and creating this “buxom” form.
These clouds form (more usually) in coastal areas where the cold air coming from the sea (and it has nothing below) comes into contact with hot air is stopped and the coast want. Although this is the common form, as I said before, they are also formed when there are two fronts collide.
Normally, the “roll” of cold air, cloud, has two forms, rack and roll depending on whether the “front” cloud which is sucking all the change in temperature and condensing the water crystals, is attached to moiety or separate this.
The most common are “stuck” or the shelf but, in the sea areas, you can see the roll.
Yes, it is important not to confuse these clouds with storm clouds or clouds that will “throw everything” because, sometimes, pulling water are those that are far behind them. These are clouds of pure and hard condensation while the others are within the area of low pressure while rain look as if “fall” down due to water are pulling away.
So, be careful about what you see those days.