The Ganges Basin to the south of Nepal occasionally sees tornadoes. Tornadoes in this region are most common during the pre- and post-monsoon months. The United States' National Centers for Environmental Information highlights an increased likelihood of tornadoes from Ganges Basin northwest along the southern slopes of the Himalayas, through Nepal, and into northeastern Pakistan. Reports of tornadoes in this region are primarily clustered in Bangladesh, with only sporadic events farther northwest. The pre-monsoon months (March to May) display the most favorable conditions for severe weather. During this time, convective available potential energy—an indicator of atmospheric instability whereby higher values denote a greater likelihood of thunderstorms—and wind shear are conducive to the development of rotating thunderstorms. Some of the deadliest tornadoes on record occur in these areas; one such tornado in 1989 killed an estimated 1,300 people in Bangladesh's Manikganj District.