Under the Köppen climate classification, Buenos Aires has a humid subtropical climate (Cfa) with four distinct seasons. As a result of maritime influences from the adjoining Atlantic Ocean, the climate is temperate with extreme temperatures being rare. Because the city is located in an area where the Pampero and Sudestada winds pass by, the weather is variable due to these contrasting air masses.
Summers are hot and humid. The warmest month is January, with a daily average of 24.9 °C (76.8 °F). Heat waves are common during summers. However, most heat waves are of short duration (less than a week) and are followed by the passage of the cold, dry Pampero wind which brings violent and intense thunderstorms followed by cooler temperatures. The highest temperature ever recorded was 43.3 °C (110 °F) on 29 January 1957.
Winters are cool with mild temperatures during the day and chilly nights. Highs during the season average 16.3 °C (61.3 °F) while lows average 8.1 °C (46.6 °F). Relative humidity averages in the upper 70s%, which means the city is noted for moderate-to-heavy fogs during autumn and winter. July is the coolest month, with an average temperature of 11.0 °C (51.8 °F). Cold spells originating from Antarctica occur almost every year, and can persist for several days. Occasionally, warm air masses from the north bring warmer temperatures. The lowest temperature ever recorded in central Buenos Aires (Buenos Aires Central Observatory) was −5.4 °C (22 °F) on 9 July 1918. Snow is very rare in the city: the last snowfall occurred on 9 July 2007 when, during the coldest winter in Argentina in almost 30 years, severe snowfalls and blizzards hit the country. It was the first major snowfall in the city in 89 years.
Spring and autumn are characterized by changeable weather conditions. Cold air from the south can bring cooler temperatures while hot humid air from the north bring hot temperatures.
The city receives 1,236.3 mm (49 in) of precipitation per year. Because of its geomorphology along with an inadequate drainage network, the city is highly vulnerable to flooding during periods of heavy rainfall.