Johannesburg features a Subtropical highland climate (Köppen Cwb). The city enjoys a dry, sunny climate with late afternoon thundershowers in the summer months of October to April. Temperatures in Johannesburg are usually fairly mild due to the city's high altitude, with the average maximum daytime temperature in January of 25.6 °C (78.1 °F), dropping to an average maximum of around 16 °C (61 °F) in June. Winter is the sunniest time of the year, with mild days and cool nights, dropping to 4.1 °C (39.4 °F) in June and July. The temperature occasionally drops to below freezing at night, causing frost. Snow is a rare occurrence, with snowfall having been experienced in May 1956, August 1962, June 1964, September 1981 and August 2006 (light). Snow fell again on 27 June 2007, accumulating up to 10 centimetres (3.9 in) in the southern suburbs. Regular cold fronts pass over in winter bringing very cold southerly winds but usually clear skies. The annual average rainfall is 713 millimetres (28.1 in), which is mostly concentrated in the summer months. Infrequent showers occur through the course of the winter months.
Despite the relatively dry climate, Johannesburg has over ten million trees, and it is now the biggest man-made forest in the world, followed by Graskop in Mpumalanga which is the second biggest. Many trees were originally planted in the northern areas of the city at the end of the 19th century, to provide wood for the mining industry. The areas were developed by the Randlord, Hermann Eckstein, a German immigrant, who called the forest estates Sachsenwald. The name was changed to Saxonwold, now the name of a suburb, during World War I. Early (white) residents who moved into the areas Parkhurst, Parktown, Parkview, Westcliff, Saxonwold, Houghton Estate, Illovo, Hyde Park, Dunkeld, Melrose, Inanda, Sandhurst, now collectively referred to as the Northern Suburbs, retained many of the original trees and have even expanded their forests with the encouragement of successive city councils. In recent years however, deforestation has occurred to make way for both residential and commercial redevelopment.