June – September
Best
The long dry season — the prime window for gorilla trekking, with firmer trails and the clearest volcano views. The busiest months, so permits go early.
December – February
Best
The short dry season — again excellent for trekking and savanna game in Akagera, warm and largely dry.
March – May & October – November
Good
The green seasons. More rain and muddier forest, but lush, quieter and good for birding — the parks stay open year-round.