 Let's see how to find the lifting condensation level, the LCL. The LCL is a level where a cloud will form if the air mass near a surface is pushed upward. We have two quantities that are conserved when lifted, potential temperature, or theta, and the water vapor mixing ratio, W. As the air parcel is pushed up, then W goes up the constant W line and theta goes up the dry adiabat, which is the constant theta line. Note that both the temperature and the dew point temperature are changing and getting closer together through each other as the air parcel ascends. When the two lines meet, the relative humidity is 100 percent, a cloud forms, and this is the lifting condensation level. Once the LCL has been reached and the cloud is formed, any further ascent will be in the cloud. The air parcel temperature will fall the moist adiabat, which is less than the dry adiabat, because as water condenses it gives up energy to warm the air a little bit. If the air were pushed down, its temperature would follow the moist adiabat as long as it was above the LCL, but below the LCL it will fall the dry adiabat and the water vapor mixing ratio will fall to the constant W1.