The column of rising air associated with a freely convecting air parcel. In "air-mass" thunderstorms, the updraft is observable as a rapidly ascending cumulus tower (cumulus calvus).
A body of air which is descending due to a density differential (colder than surrounding air) and is accompanied by precipitation.
Planetary Boundary Layer (PBL)
The lowest level of the troposphere, meaning the level of the atmosphere which is nearest the Earth's surface. This layer generally becomes stable (cools with height) at night due to radiative cooling, while becoming highly unstable during daytime hours due to solar heating.
Lifted Condensation Level (LCL)
The level at which an air parcel has adiabatically cooled to its dewpoint, causing condensation.
Level of Free Convection (LFC)
The level at which an air parcel begins to rise freely due to being warmer than its surrounding environment, therefore being positively buoyant.
In order for thunderstorms to develop, three essential elements must be present: sufficient moisture (to allow for cloud development), instability (air parcels must, at some point, be warmer than the environment), and a lifting mechanism (to "force" air parcels to begin rising).