Bam is in the Kerman province desert of southeastern Iran and the climate is extreme. Summers (June to August) are brutally hot, with temperatures regularly exceeding 45°C. The best time to visit is autumn through spring: October to March offers warm days and cool nights, with January and February occasionally chilly. March brings the Persian New Year (Nowruz) when many Iranians travel and the country's sites are busy; February is a good compromise — mild weather and fewer crowds.
The date harvest runs from August through September; if you want to see the oasis at its most active and buy fresh Mazafati dates, this is the time, despite the heat. Foreign visitors to Iran should check the current visa situation and travel advisories before planning a trip; independent travel is possible but requires some advance organisation including an Iranian-sponsored visa.