Average temperatures in city center are 37 F (3°C) in January with 28°F (-2°) for the minimum and 77 (25°C) in July with average maximum of 86 F (30°C). Snowfalls are relatively common during winter but with few days with snow. The historic average of Milan's area of 8,2 (21 cm)in the period between 1950 and 2007; with a record of 27,5 in (70 cm) during the famous snowfall of January 1985. Humidity is quite high during the whole year and annual precipitation averages about 1000 mm (40 in). The ventilation is poor throughout the year and this increases the rate of pollution. In the stereotypical image, the city is often shrouded in the heavy fog characteristic of cold seasons in the Po Basin, although the removal of rice paddies from the southern neighbourhoods, the urban heat island effect and the reduction of pollution from factories have reduced this phenomenon in recent years, at least in the city centre but the pollution is still very high. Wind is generally absent. In spring, though, gale-force windstorms can happen, generated either by Tramontana blowing from the Alps or by Bora-like winds from northeast.