Monday, January 28, 2008

Roll clouds are tubular shaped clouds associated with storms or advancing cold fronts. They're formed when down drafts usher in cold air toward the ground. This colder, denser air then spreads out along the surface in the direction the storm or front is advancing and undercuts warmer air. When moisture in this tumultuous near-surface air condenses, and if conditions are favorable, a roiling, rolling cloud occasionally forms.

From here.



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