The Fouta Djallon has two seasons. The dry season runs roughly November to April: the trails are clear, the days are sunny and mild at altitude, and the roads are passable. This is the easiest time to travel but the waterfalls will be at lower volume or reduced to trickles by March and April.
The rainy season (May to October) brings daily thunderstorms, dramatic cloud formations over the plateau, and the waterfalls at their full, thundering best. Roads become muddy and some tracks are impassable for ordinary vehicles. Trekking is muddier and harder but the landscape is a vivid green and the waterfalls justify the discomfort. Ditinn Falls are most spectacular in July–September.
The highlands are noticeably cooler than the Guinean coast throughout the year — temperatures rarely exceed 28°C even in the dry season, and nights can be cold. Pack a layer.