The first stage of a thunderstorm begins with instability, which creates potential energy, and a mechanism to release the instability or create lift. Instability is created when the warm air inside a cloud is warmer than the surrounding environment. Lift can be created by a front, such as a cold or warm front, an area of low pressure (low pressure trough), or air rising up a slope. As the air rises, some of this air condenses to form the water droplets of the cloud; the energy released (latent heat) warms the air inside the cloud causing further instability. The amount of instability determines the strength of the upward motion of the air (updrafts) and the height of the cloud that is formed. and thus the severity of the storm; the degree of instability is determined by the degree of warmth of the air within the cloud and the amount of time during which the air inside the cloud remains warmer than the surrounding environment. The warmer the air within the cloud and the longer that this air remains warm will increase the instability of the air and the severity of the storm. As more air condenses, some of the water droplets fall to the ground within sinking air (downdrafts) located in front of the storm.