Niš has a continental climate — hot summers and cold winters. The best months for visiting are May–June and September–October, when temperatures are comfortable (18–26°C) and the outdoor terraces are in full swing without the brutal heat of July and August. Summer evenings are pleasant enough; daytime can reach 35°C or more, which makes touring archaeological sites less enjoyable.
The NIŠville Jazz Festival takes place in August and has grown into one of the region's major music events, drawing acts from across Europe and beyond. The city fills up and accommodation prices rise. If music is your reason for coming, this is when to go; if you prefer a quieter visit with easier access to the sights, aim for late spring or early autumn.
Winter is cold, occasionally snowy, and quiet. The main indoor sights — the concentration camp museum, the Skull Tower chapel — remain open year-round.