Gorillas can actually be spotted throughout the year in Bwindi Impenetrable Forest, which is the best place to see them in Uganda. It can rain at any time during the year, but generally the driest months are between December and January, as well as from June to August. These are understandably the most popular periods to visit, when ground conditions make hiking through the rainforest more enjoyable.
Photo Credit: Gorilla Forest Camp
Yet come out of peak season and the experience can be equally special. Accommodation rates will be lower, and the country will be less crowded. Not that it ever really gets busy in Uganda! However, do bear in mind that gorilla trekking is more difficult during the wet season when the rains will have made trails muddy and the forest floor slippery. You might not have to trek as far though, as gorillas are known to hang out on the lower, warmer slopes during rainy weather.
Chimpanzee trekking can also be enjoyed year-round in Kibale Forest National Park, with weather conditions similar to those in Bwindi. It will be drier between December and February, and also in June and July, so if you want to avoid the mud, time your visit to fall during these months.