Sydney has a temperate climate with warm summers and mild winters. Rainfall is spread throughout the year. The weather is moderated by proximity to the ocean, and more extreme temperatures are recorded in the inland western suburbs. The warmest month is January, with an average air temperature range at Observatory Hill of 18.6-25.8 °C (65-78 °F). An average of 14.6 days a year have temperatures of more than 30 °C (86.0 °F). The maximum recorded temperature was 45.3 °C (113.5 °F) on 14 January 1939 at the end of a four-day heatwave across Australia.

In winter, temperatures rarely drop below 5 °C (41 °F) in coastal areas. The coldest month is July, with an average range of 8.0-16.2 °C (46-61 °F). The lowest recorded minimum at Observatory Hill was 2.1 °C (35.8 °F).

Rainfall is fairly evenly spread through the year, but is slightly higher during the first half of the year, when easterly winds dominate.[citation needed] The average annual rainfall, with moderate to low variability, is 1,217 mm (48 in), falling on an average 138 days a year. Snowfall was last reported in the Sydney City area in 1836. However, a July 2008 fall of graupel, or soft hail, mistaken by many for snow, has raised the possibility that the 1836 event was not snow, either.

Partially cloudy with periodic sunshine during the Spring season, looking out towards Sydney's Dover Heights .
Bondi BeachThe city is not affected by cyclones. The El Niño Southern Oscillation plays an important role in determining Sydney's weather patterns: drought and bushfire on the one hand, and storms and flooding on the other, associated with the opposite phases of the oscillation. Many areas of the city bordering bushland have experienced bushfires, notably in 1994 and 2001-02 - these tend to occur during the spring and summer. The city is also prone to severe hail storms and wind storms. One such storm was the 1999 hailstorm, which severely damaged Sydney's eastern and city suburbs. The storm produced massive hailstones of at least 9 cm (3.5 in) in diameter and resulting in insurance losses of around A$1.7 billion in less than five hours.

The city is prone to flash flooding from rain caused by East Coast Lows (a low pressure depression which can bring significant damage by heavy rain, cyclonic winds and huge swells). The most notable event was the great Sydney flood which occurred on 6 August 1986 and dumped a record 327.6 mm (12.9 in) on the city in 24 hours. This caused major traffic problems and damage in many parts of the metropolitan area.

The Bureau of Meteorology has reported that 2002 through 2005 were the warmest summers in Sydney since records began in 1859. 2004 saw an average daily maximum temperature of 23.39 °C, 2005 of 23.35 °C, 2002 of 22.91 °C, and 2003 of 22.65 °C. The average daily maximum between 1859 and 2004 was 21.6 °C (70.9 °F). For the first nine months of 2006 the mean temperature was 18.41 °C (65.1 °F); the warmest year previously was 2004 with 18.51 °C (65.32 °F). Since November 2003, there have been only two months in which the average daily maximum was below average: March 2005 (about 1 °C below average) and June 2006 (0.7 °C below average).

The summer of 2007-08 proved to be one of the coolest on record. The Bureau of Meteorology reported that it was the coolest summer in 11 years, the wettest summer in six years, and one of only three summers in recorded history to lack a maximum temperature above 31 °C (88 °F).

The average annual daytime temperature at Observatory Hill was 22.9 °C (73.2 °F), which was 0.9 °C above the historical annual average. This ranks as 7th highest annual average maximum temperature since records commenced in 1859. During the year, average night-time temperatures at Sydney Observatory Hill were at 15.1 °C (59.2 °F), which was 1.2 °C above the historical average.

In the first weeks of February 2010, Sydney received some of the highest rainfalls in years, which caused flash flooding and traffic chaos. On 4 February, some suburbs in the North Shore region recorded their heaviest rain in 20 years. On 12 and 13 February, some suburbs were hit by thunderstorms which brought heavy rain and gusty winds which cut out power and damaged homes. On 13 February, Sydney experienced one of the highest rainfall of the last decade with 65 millimetres (2.6 in) of rain falling in one night at Observatory Hill. The heavy rain was caused by remnants of ex-tropical Cyclone Olga and humid north-easterly winds feeding into the low pressure trough.