Isfahan has a semi-arid continental climate: hot, dry summers and cold winters, with most rainfall in spring and autumn. The best times to visit are spring (March–May) and autumn (September–November), when temperatures are mild and the light is particularly good for the city's architecture. Spring is especially pleasant — the gardens along the river are in bloom and the weather is ideal for outdoor walking.
Summer (June–August) can be very hot, with temperatures regularly exceeding 35°C. If you visit in summer, plan sightseeing for early mornings and evenings. Winter (December–February) is cold and can see frost and occasional snow, but visitor numbers are low and the light on the tiled domes can be beautiful.
Nowruz (Persian New Year, around 21 March) is worth timing a trip around if you can — the city fills with Iranian tourists, gardens are decorated, and the atmosphere around Naqsh-e Jahan Square is festive. Book accommodation well in advance for the Nowruz week.