Datong sits at around 1,000 metres altitude on the dry northern plateau, with cold, windy winters and warm summers. Spring and autumn are the most comfortable seasons. May and September are good months: clear skies, moderate temperatures, and smaller crowds than the summer peak.
Summer (July and August) brings school holidays and Chinese domestic tourism in force — the Yungang Grottoes and the Hanging Monastery can become very crowded on weekends and during Golden Week (the first week of October). If you visit in summer, arrive at major sites as early as possible.
Winter is cold — daily temperatures frequently drop well below freezing — but the crowds thin dramatically and the grottoes have an austere quality in the low winter light. Snow is relatively rare but possible from November through March. The Hanging Monastery may close in deep winter.