Lumbini sits in the Terai lowlands and shares the climate of the north Indian plain: a sweltering summer, a humid monsoon, and a clear dry winter.
October to March is the comfortable season — dry, cool nights, warm days, fields green from the recent monsoon. December and January can be foggy in the early mornings; the fog usually burns off by 10 am. April and May are punishingly hot (over 40 °C is normal) and dusty. The monsoon from June to September is hot and wet; mosquitoes are bad, and the Sacred Garden floods in places.
Buddha Jayanti in May is the major pilgrimage date when the site fills with monks and visitors from across Buddhist Asia. The atmosphere is extraordinary; book accommodation well ahead.