The meteorological conditions change over the day and the year and vary a lot depending of the terrain conditions. The meteorological parameters govern both the wind turbine emission sound level and the sound propagation conditions. Long-time measurements of meteorological effects on sound propagation from wind turbines have been performed at three sites in Sweden. The measurements have been performed during 2 years. Sound propagation is studied in a forest area, over a water bay and over heterogeneous terrain. The first two sites are located in the southern part of Sweden and the third is located in the northern part of Sweden. The aim of the project is to improve the knowledge about sound propagation from wind turbines and especially over varying terrain and different weather conditions. The hub height of the studied wind turbines varies from 80-138 m. Meteorological effects increase with distance and starts to be important somewhere between 400 m – 1000 m. Variations of 7-14 dBA at the immission point are found depending on ground conditions and refraction.