Asunción has a humid subtropical climate that closely borders on a tropical savanna climate (Köppen Aw), characterized by hot, humid summers (average of 27.5 °C or 81.5 °F in January), and mild winters (average of 17.6 °C, 63.7 °F in July). Relative humidity is high throughout the year, so the heat index is higher than the true air temperature in the summer, and in the winter it can feel cooler. The average annual temperature is 23 °C (73 °F). The average annual precipitation is high, with 1,400 millimeters (55 in) distributed in over 80 days yearly. The highest recorded temperature was 42.8 °C (109.0 °F) on 1 October 2020, while the lowest recorded temperature was −1.2 °C (29.8 °F) on 27 June 2011.
Snow is unknown in modern times, but it fell during the Little Ice Age, last time in June 1751.
Asunción generally has a very short dry season between May and September, but the coldest months are June, July and August. Slight frosts can occur on average one or two days a year. The wet season covers the remainder of the year.
During the wet season, Asunción is generally hot and humid though towards the end of this season, it becomes noticeably cooler. In contrast, Asunción’s dry season is pleasantly mild. Asuncion’s annual precipitation values observe a summer maximum, due to severe subtropical summer thunderstorms which travel southward from northern Paraguay, originating in the Gran Chaco region of the northwestern part of the country. The wettest and driest months of the year are April and July, on average receiving respectively 166 mm (6.54 in) and 39 mm (1.54 in) of precipitation.