The mean annual temperature in Bulgaria is 10.6 °C and varies from 2.9 °C at the nation's highest peak Musala to 13.9 °C at the town of Sandanski in the southern Struma valley. The average temperature in the Danubian Plain is 11.4 °C, in the Upper Thracian Plain 13.9 °C, in the lower mountains 8.1 °C and in the higher mountains 2.4 °C. The highest absolute temperature was measured at the town of Sadovo in 1916  45.2 °C; the lowest absolute temperature was measured at the town of Tran in 1947 –38.3 °C. The highest temperature in the lowlands and the hilly regions is in June, while in the higher mountains the warmest month is August. The lowest temperature is measured in January and February, respectively. Many valleys experience regular temperature inversions and fogs in winter. The country's lowest absolute temperature was measured during an inversion in the Tran valley.