Vento Foehn   The figure shows what happens when an air parcel with a temperature of 20 degrees centigrade and a relative humidity of 57% is forced to cross a mountain range with an altitude of 2 500 m. The dew point is reached at 900m and clouds are formed. The air is cooled by approximately 1 degree centigrade per 100 metres until the dew point is reached. Above the condensation level the air is cooled at a lapse rate of 0.5 degrees centigrade per 100m. So the temperature of the air at the top of the range will be 3 degrees centigrade.