Time your visit with Rwanda's seasons
Dominated by tropical rainforest, Rwanda’s climate is fairly consistent all year round with high temperatures and high levels of rainfall. Whenever and wherever you visit, you can expect to receive a fair amount of sunshine. That said, you will almost inevitably encounter some rainfall too in the forest regions of Volcanoes and Nyungwe.
For a general rule though, Rwanda does follow the same typical weather patterns of East Africa with the two 'dry seasons' Dec-Feb and Jun-Oct and the two 'green seasons' Mar-May and November.
Peak season is in August and between December and January. If you are planning a trip, it may be worth trying to avoid these periods if possible. Rainfall does rise slightly between March to May and October to November, although only marginally.