A parcel is large enough to contain a very great number of molecules, but small enough so that the properties assigned to it are approximately uniform throughout. The spreading of the upper portion of a cumulonimbus cloud that takes on the form of an anvil, typically fiberous or smooth in appearance. That property of an object that enables it to float on the surface of a liquid, or as in the case with air parcels, to ascend and remain freely suspended in the atmosphere. For a given cloud or cloud layer, it is the lowest level in the atmosphere where cloud particles are visible. The air behind a cold front is cooler and typically drier than the air it is replacing.
Sublimation is the process by which a solid forms directly from vapor.
In general, mass motions within a fluid resulting in transport and mixing of properties of that fluid. Forced Convection is the ascent of air induced by some external force. An example of this convection is the lifting of lighter, warmer air by an advancing cold front. Other examples include convection resulting from orographic lifting and convergence. Free Convection is the rising of heated air and the sinking of cooler air without the need of external forces.