The south western parts of Uganda straddle the equator and enjoy a pleasant climate all year round, even at the higher altitudes of Mgahinga and Bwindi Impenetrable Forest National Parks. Here one might need a light jersey in the evening and certainly rain gear while tracking gorillas, but while some days are humid and even hot, the nights are usually comfortably cool.
In Queen Elizabeth National Park the lower altitudes mean that conditions are generally warmer, but heading north along the Albertine Rift to the Ruwenzori Mountains temperatures drop sufficiently to allow it to snow at the higher altitudes.
Further north the tropical vegetation and soils make way for more arid savannah, things becoming drier the further north one heads. Some forest patches exist in wetter areas south of Murchison Falls National Park, but Kidepo in the north of the country shares affinities with northern Kenyan arid savannah.
Uganda experiences two rainy seasons a year: the long rainy season lasts from mid-February to early-June, while there is a second shorter rainy season between mid-September and mid-December. It equatorial location means one should always be prepared for precipitation however and it can be considered appropriate to visit at any time of the year.