The best time to visit Ulaanbaatar is June to September. Summers are warm and dry (daytime temperatures around 25–30°C), the steppe turns green, and the Naadam Festival in mid-July is the highlight of the Mongolian calendar. July is the peak tourist month — book accommodation and Trans-Mongolian Railway tickets well in advance.
Spring (April–May) is transitional — cold nights, unpredictable weather, and occasional dust storms, but fewer crowds. Autumn (September–October) is quieter and the light is golden.
Winter is genuinely extreme: temperatures regularly drop to -30°C and occasionally lower, and the city suffers from severe air pollution as every ger district household burns coal and wood for heat. UB is consistently ranked among the most polluted cities in the world in winter. That said, winter has its own appeal for the adventurous — the city feels authentically Mongolian when the tourists are gone, the steppes are frozen white, and the sky above the smog layer is brilliant blue.