Nanchang City has a subtropical monsoon climate, characterized by mild and humid conditions, abundant sunshine, long summers and winters, and short springs and autumns. Winters are cold and summers are hot, autumns are crisp and springs are chilly. Spring and summer are rainy, while autumn and winter are dry. The frost-free period is long, and the freezing period is short. Average temperatures vary significantly: spring average 17.5℃, summer average 28.2℃, autumn average 20.9℃, and winter average 6.3℃. The annual average temperature is 17.1℃, with an extreme high of 40℃ (August 2, 2003) and an extreme historical low of -15.2℃ (February 9, 1972).
Nanchang City receives abundant rainfall, with an annual average of 1559.8 mm (1959-2019). Monthly rainfall is unevenly distributed, with concentrated rainfall from April to June, averaging 741.7 mm, accounting for 47.55% of the annual rainfall. This period is also the most prone to geological disasters, often leading to floods. Rainfall from November to January of the following year accounts for only 10.85% of the annual total. The highest annual rainfall was 2265.1 mm (1998), the lowest was 1019.6 mm (1964), and the highest daily rainfall was 228.8 mm (June 25, 2003).
Nanchang City receives 1723-1820 hours of sunshine annually, with a sunshine rate of 40%. The sunshine hours are highest in July and August and lowest in February and March. The distribution of sunlight is largely synchronized with the peak growing season for crops, which is beneficial to agricultural production. The average total solar radiation from 1986 to 2003 was 4279.02 MJ/m², and the average net solar radiation from 1992 to 2003 was 2078.67 MJ/m². Because wind speed is greatly affected by topography and geographical location, parts of Nanchang, Xinjian, and Jinxian are adjacent to Poyang Lake and experience strong winds, making them suitable areas for wind energy utilization. Anyi, however, is not adjacent to Poyang Lake, and except for special topography, experiences weak winds and has no wind potential; its average annual wind speed is 2.3 m/s. The frost-free period is 251-272 days per year. Suitable for plant and flower growth, it is an ideal area for creating a "garden city."