It should be remembered that CAPE represents potential energy, and will only be used should a parcel be lifted to the level of free convection. When values are above 3500 j/kg and storms do develop, they may build rapidly and quickly become severe. Often these storms are referred to as "explosive storms" by chasers and professionals. In a high CAPE environment storms that develop can usually be seen by the human eye as rising rapidly. Chasers discussing these kind of storms have been overheard saying these storms resemble a nuclear explosion as in this photo, because they rise up so quickly and powerfully.
Joules Defined: Energy here is expressed in JOULEs (J). An energy of 1 joule is expended in moving an object through 1 meter when it is opposed by a force of 1 NEWTON. 1 Joule is equal to 1 Newton-meter. Energy is stored work, Work being the application of a force through a distance. Power is the rate of flow of energy, or the rate at which work is done. Stored energy becomes working energy when it is used.
CAPE is then expressed as: Joules J (Energy) /kg Per Kilogram (Mass)
NOTE: To get the full picture of severe weather potential CAPE should be used in conjunction with a full sounding. Also remember that CAPE when used to calculate (Wmax), is often over stated by as much as a factor of 2x.
For more details take a class on Buoyancy and CAPE by clicking here. This class room study requires flash player to be installed on your web browser. A teacher will explain step by step buoyancy and CAPE. The class is free online right now.