Lubango sits at around 1,700 metres, which gives it one of the most comfortable climates in Angola. It is never tropical-hot and never cold enough to be a problem, though you will want a layer in the evenings year-round. The altitude means the seasons play out differently than on the coast.
The dry season runs from roughly June to September and is the best time for the main day trips. Views at the Tundavala Gap are sharpest in the dry months when the air is clear, and the Serra da Leba road is at its most photogenic without cloud obscuring the drops. Be aware that June and July mornings can be genuinely cold — single figures overnight — so pack accordingly. The rainy season from November through April brings afternoon thunderstorms that build quickly, clearing usually by evening, and keeps the plateau remarkably green. August is the peak of the dry season and also the month of the Festa da Nossa Senhora do Monte, when the cathedral draws pilgrims from across Huíla province — a worthwhile reason to time your visit around it.