Ujjain has a continental climate. Winters (November to February) are the most comfortable time to visit, with cool days and cold nights — ideal for temple visits and walking the ghats without the oppressive heat. The monsoon (July to September) brings heavy rain that turns the Kshipra River fast and brown, but the city remains active and the rain itself is an experience.
Summer (April to June) is hot and exhausting, with temperatures regularly exceeding 40°C. Not recommended unless you have no choice.
The most important event is the Simhasta Mela (Ujjain Kumbh Mela), held every twelve years when Jupiter enters Leo. Millions of pilgrims converge on the city over several weeks to bathe in the Kshipra. The next Simhasta is due in 2028. If it coincides with your travels, the spectacle is extraordinary but infrastructure is stretched to breaking — plan well in advance or expect chaos.
The smaller Ardh Kumbh (half-Kumbh) occurs six years after the main mela, drawing somewhat fewer millions.