This figure shows a mass of moist air moving into Colorado from the southwest. At the western base of the mountains, the elevation is 1800 m, and the temperature of the air is 20C. The air mass is forced to rise over the San Juan Mountains where it condenses and precipitates on the windward side. It eventually descends into the San Luis Valley on the leeward side of the mountains at about 2100 m. What is the temperature (in degrees Celsius) at 2500 m (the elevation at which condensation begins?)