Spring

Springs in Buenos Aires are typically mild during the day with cool to cold nights.^[29] The average high is 22.8 °C (73.0 °F) while the average low is 13.4 °C (56.1 °F).^[29] It is one of the rainiest seasons in the city, averaging 320.5 mm (12.62 in) of precipitation and 28 days with measurable precipitation.^[29] Nonetheless, most precipitation events are short in duration.^[6] Spring is characterized by changeable weather with temperatures that can fluctuate.^[30] Cold polar air from the south can bring cooler temperatures. An extreme example of this was in November 2007, when cold polar air from the south brought temperatures down to 2.5 °C (36.5 °F) on the morning of 15 November.^[31] The same polar air affected many parts of the country, bringing cold temperatures and snow in coastal parts of Patagonia.^[31] In contrast, hot humid air from the north produces sultry days;^[12] the highest temperature recorded in spring is 36.8 °C (98.2 °F) on 27 November 1955.^[29] In some cases, heat waves,^{[note 2]} can occur, particularly in November.^[32]

Summer

Summers are hot and humid.^[6] On average, mornings and afternoons are hot whereas temperatures drop considerably at night.^[6] The average high is 29.3 °C (84.7 °F) while the average low is 19.4 °C (66.9 °F).^[33] With a mean precipitation of 386.5 mm (15.22 in), it is the rainiest season.^[33] This is due to high temperatures and high insolation that lead to the development of a low pressure system called the Chaco Low situated over northern Argentina that interacts with the South Atlantic High to generate a pressure gradient that brings moist easterly winds to the region, favouring precipitation, which mostly occurs in the form of convective thunderstorms.^[34][35] The Chaco Low also interacts with the South Atlantic high to bring warm and tropical air from the north which is the strongest in summer when the Chaco Low is at its strongest due to higher insolation.^[10]

Heat waves are a common feature of summers in the city.^[33] These heat waves place extra demand on electricity usage, leading to shortages.^[36][37] In extreme cases, these power shortages during heat waves can cause traffic jams and protests, such as the ongoing 12-day March 2023 heat wave, the longest heat wave ever recorded in Buenos Aires^[38] However, most heat waves are less than a week long,^[33] and are followed by the passage of the cold, dry Pampero wind, which brings violent and intense thunderstorms with strong gusts and hail followed by cooler temperatures and lower humidity.^{[12][13][39][40]} Occasionally, a tornado can form, which can strike the city; most tornadoes are relatively weak and rarely cause deaths.^[41] The greatest risk for tornadoes occurs in summer due to favourable conditions.^[41] These severe storms can damage cars, houses and disrupt public services such as transportation and collection and disposal of urban solid waste.^[42]: 39

Autumn

At the beginning of autumn, temperatures are warm to hot in the afternoon while nights and mornings are mild.^[43] Later on in the season, conditions are cooler featuring mild afternoons, and cold nights and mornings.^[43] The average high and low are 23.2 °C (73.8 °F) and 14.3 °C (57.7 °F) respectively while precipitation averages 343.8 mm (13.54 in) during this season.^[43] Similar to spring, the season is characterized by changeable weather conditions with temperatures that can fluctuate;^[30] temperatures as high as 37.9 °C (100.2 °F) and as low as −4.0 °C (24.8 °F) have been recorded.^[43] Periods of rainy weather occur although these are usually of short duration.^[6] Frosts rarely occur, though they can occur as early as May.^[44]

Winter

June to August are the winter months in Buenos Aires.^[45] Winters are cold with mild temperatures during the day and cold nights.^[6] Highs during the season average 16.6 °C (61.9 °F) while lows average 8.3 °C (46.9 °F).^[45] Lows rarely drop below freezing, with the average annual lowest temperature being 0 °C (32.0 °F) at the central observatory. Cold waves can occur in these months in which periods of cold temperatures can persist for days.^{[45][note 3]} These cold waves, particularly during severe winters lead to increases in energy demand, which can cause significant energy shortages.^[3] Snowfall occasionally occurs in the surrounding areas of the city but rarely within Buenos Aires proper; since the start of meteorological observations in 1906 at the central observatory, snowfall has only been observed thrice: June 1918, July 1928, and July 2007.^[3] This is due to the city center having higher temperatures than the surrounding areas owing to the urban heat island effect.^[3][11]

Most of the precipitation comes from frontal systems associated with cyclogenesis and strong southeasterly winds (Sudestada), which bring long periods of precipitation, cloudy weather and cooler temperatures.^[16][17][18] Winters are cloudy while relative humidity is very high, often 90% or higher, making the weather dull, grey and cool.^[47] Occasionally, warm air masses from the north bring warmer temperatures.^[7] These warm air masses can bring sunny weather, particularly during the afternoon when they come from the north or northwest as a result of a trough located in central Argentina.^[7] On the other hand, warm air masses from Brazil bring humid conditions, featuring high humidity with high cloud cover that is typical of a warm front of a frontal system and typical of tropical maritime air.^[7] These warm air masses that are responsible for the high humidity and cloud cover are the warmest air masses, leading to the warmest temperatures.^[7] Nonetheless, these are short lived as the Chaco Low, which is responsible for bringing in warm and tropical air from the north is weaker in winter due to lower insolation, leading to the winds from the north being less intense and shorter lived.^[10]

Towards the end of winter in August, there are important changes in the atmospheric circulation.^[48] Warm, humid air penetrates the city, higher solar radiation and frequent synoptic weather disturbances from the west occur during the end of the winter.^[48] As such, the end of winter is usually characterized by heavy storms with lightning.^[48][49] This is popularly known as the Santa Rosa Storm, around 30 August.^[48][49] Based on 111 years of weather observations (1906–2016) from the central observatory, 61 years (55% of the time) have seen stormy weather occurring on days close to 30 August, although not all of these have led to heavy precipitation.^[48]

Temperature

According to the central observatory, which has one of the most reliable and oldest records in South America,^[3] the highest temperature in Buenos Aires, 43.3 °C (109.9 °F), was recorded on 29 January 1957 while the lowest temperature recorded is −5.4 °C (22.3 °F) on 9 July 1918.^[50] The warmest year on record is 2017, with a mean annual temperature of 18.7 °C (65.7 °F) or 18.8 °C (65.8 °F).^[51] On the other hand, 1911 was the coldest year, with a mean annual temperature of 15.4 °C (59.7 °F).^[52]

Precipitation

The year with the maximum precipitation was 1900, when the city received 2,024 mm (79.7 in) of precipitation.^[65] On the other hand, 1916 has been the driest year, with a mean annual precipitation of 504 mm (19.8 in).^[66] The highest precipitation for a single day was recorded on 27 February 1930, when 194.1 mm (7.64 in) of precipitation fell.^[33]