Why is there no high temperature weather in Lushan Mountain?

All the peaks of Lushan Mountain are above 1000 meters above sea level. There are dense forests on the mountains and rivers and lakes under the mountains. Coupled with the perennial rain and high air humidity, the temperature difference between mountains in summer is caused. In midsummer every year, the sun is blazing in Poyang Lake basin, and the highest temperature can reach above 39℃, while the average temperature on the mountain is only about 22.6℃ in summer, and the temperature is often between 15-20℃ in the morning and evening.