Nyeri's altitude — about 1,750 metres — keeps the climate cool and green almost year-round. There are two rainy seasons: the long rains from late March through May and a shorter pattern of showers in October and November. Both can turn the dirt roads in the Aberdares to mud and make game-viewing harder.
The driest and clearest months are January–February and July–September, when Mount Kenya is more often visible from town in the morning. Nights at this altitude are surprisingly cold even in the dry season — bring a fleece. The town is at its best on a clear morning when the snow on Mount Kenya shows above the eastern ridges.