Johannesburg has a relatively mild climate, with warm, dry summers and moderate winters.  Travelers from cooler climates sometimes find that the summers are a bit too warm for them, but it is a generally dry heat which makes it relatively comfortable for people who are from more humid locations. 

The rainy season in Johannesburg begins in October and continues through April, with intermittent mild showers occurring throughout that season.  Winters are very dry, generally mild with cold clear evenings and bright, sunny days with mild to warm temperatures. Snow and rain in the winter time are almost unheard of.

Travelers interested in spending time in the area during the local events and festivals which characterize the culture there will probably find that autumn is the season to head to Johannesburg.  Many art festivals take place there at that time.  More information on annual events there is available at http://www.tripadvisor.com/Travel-g31... .