Climate of Sydney
The climate of Sydney is humid subtropical (), shifting from mild and cool in winter to warm and hot in the summer, with no extreme seasonal differences as the weather is moderated by proximity to the ocean, although more contrasting temperatures are recorded in the inland western suburbs. Despite the fact that there is no distinct dry or wet season, rainfall peaks in the first few months of the year and is at its lowest just around the middle of the year, though precipitation can be erratic throughout the year. Precipitation varies across the region, with areas adjacent  to the coast being the wettest. According to the Bureau of Meteorology, Sydney falls in the temperate climate zone which has warm to hot summers and no dry season. Sydney's plant hardiness zone ranges from zone 11a to 9b throughout the metropolitan area. Sydney has 109.5 clear days and 127.2 cloudy days annually, though it would have over 300 days of visible sunshine if one would count partly cloudy days or sunny breaks. Overall, Sydney has just about 66% of possible sun for Jun-Aug and around 54% for Dec-Feb, making winter sunnier than summer on average. Sydney 's heat is predominantly dry in spring, but usually humid in the summertime. On some hot summer days, low pressure troughs increase humidity and southerly busters decrease temperatures by late afternoon or early evening. In the warm season, particularly late summer and early autumn, troughs combined with a humid air mass can bring large amounts of rainfall, and in late autumn to early winter, the city can be affected by east coast lows. When the subtropical ridge is north of Sydney in late winter to early spring, the wind would come from the west or inland. As the ridge moves  south in summer and autumn, the winds become easterly. Sydney experiences an urban heat island effect, making certain parts of the city more vulnerable to extreme heat, particularly the west. Efforts have been introduced to investigate and mitigate this heat effect, including increasing shade from tree canopies, adding rooftop gardens to high rise structures and changing pavement colour. The El Niño Southern Oscillation, the Indian Ocean Dipole and the Southern Annular Mode play an important role in determining Sydney's weather patterns: drought and bushfire on the one hand, and storms and flooding on the other. Sydney is prone to  heat waves and drought, which have become more common in the 21st century. Furthermore, the region of Sydney, and as well as the rest of the New South Wales coastline, is warmed by the East Australian Current. Seasons. Summer. Summer in Sydney tends to vary, but it is generally warm to hot. Though at times, sea breezes would moderate the temperatures and raise humidity. Temperatures tend to be stable in late summer where temperature maxima rarely goes below or over , unlike late spring and early summer where such extremes would occur. Summer is often humid, particuarly late summer – However, when  temperatures soar over , the humidity is generally low as such high temperatures are brought by searing winds from the Australian desert. Sydney summers are characterised by rapid changes of weather, with humidity and rain not uncommon to the city although thunderstorms are more common in the west. The ultraviolet index rating in the summer averages at 12, but can reach 13 in the midst of the season, which may lead to skin damage among those having light skin. When temperatures reach over , the relative humidity seldom exceeds 45%, although low pressure troughs can increase humidity in some hot days, especially  in late summer, where they may provide afternoon thunderstorms that are usually accompanied by heavy rainfall and, at times, hail. Furthermore, most mornings and nights would be muggy, with the 9am relative humidity ranging from 69% to 75%. The average 3pm dewpoint temperature in the summer ranges from at the coast, to inland. Dewpoints would be higher in late summer, reaching , especially in the mornings and evenings, although they would usually be lower in the heat of the day, dipping as low as in the extremely hot day. In late spring and summer, Sydney can sometimes get northwesterly  winds from the Outback, which are dry and hot, making the temperatures soar above , with the relative humidity as low as 15%. This happens after the northwesterlies are carried entirely over the continental landmass, not picking up additional moisture from a body of water and retaining most of their heat. On these occasions, Sydney can experience the fury of the desert climate, although they are often ended with a Southerly Buster, which is a windy, shallow cold front that sweeps up from the southeast abruptly cooling the temperature. At times, it may be accompanied by a thunderstorm and drizzle, and  it may keep the temperatures cool the following few days as well. These strong, hot, northwesterly winds from the interior always precede a vigorous, westerly cold front (which usually drags warm inland air towards the southern and eastern coasts). In the Sydney central business district, an average of 15 days a year have temperatures of more than and 3 days with temperatures over . In contrast, western suburbs such as Liverpool and Penrith have 41 and 67 days with temperatures above , 10 and 19 days above , and, 1 and 4 days above , respectively. The highest recorded maximum temperature at Observatory Hill  was on 18 January 2013 during a prolonged heat wave across Australia from early December 2012 to late January 2013. The highest recorded minimum at Observatory Hill is , registered on 6 February 2011. A similar minimum temperature has also been recorded in the western suburbs. The highest recorded maximum temperature for the western suburbs was recorded at Penrith with a high of 48.9 °C (120 °F) on 4 January 2020. Autumn. Late summer conditions usually continue until the first few weeks of April where maximum temperatures hover around and with the dewpoint being around and on average. Although , unlike late summer, the nights may be seemingly cooler and crispier. Most heavy rainfall events usually occur in late summer and early autumn as the subtropical ridge of high pressure, which rotates counterclockwise, is to the south of Australia and would therefore give way for moist easterlies from the Tasman Sea and as well as low pressure systems to penetrate the region. The transition from late summer to autumn is gradual, where noticeably cooler and crisper conditions taking in effect by around mid-April. In mid-autumn, the highs typically average at a pleasant or 23 °C (73 ° F), rarely going above or below . In May, the average highs would be around and with cool and usually humid nights, that seldom dip below . Wintry highs of may be expected in the last week of autumn. Temperatures in autumn are usually consistent and stable, lacking any extremes that tend to be experienced in spring and summer. Due to moist easterlies that prevail in this season, foggy mornings should be expected. The average 9am relative humidity in autumn ranges from 72% to 80% in the Sydney region, the highest in the year. The lowest maximum temperature in autumn is  , recorded on 24 May 1904. Winter. In winter, the diurnal range in the western suburbs is relatively high, with temperatures being as high as during the day and as low as at night. Such low temperatures may provide mild to moderate frost in the western suburbs. Winter in central Sydney tends to be more mild where the lows rarely drop below , and highs hovering at around 16 °C (61 °F) and 17 °C (63 °F) mainly due to proximity to the ocean. Furthermore, it is worth noting that Sydney CBD (Observatory Hill) has never recorded frost , whereas coastal cities in the country on similar latitudes, such as Perth, Esperance and Adelaide, and those further north of Sydney such as Coffs Harbour, Port Macquarie, Hervey Bay and Sunshine Coast, have recorded frost or temperatures below . In the west, Liverpool and Richmond have 4 and 38 nights, respectively, where temperatures dip below . On average, only 1 night in Liverpool and 17 nights in Richmond have lows going below . The lowest maximum temperature in Liverpool was , recorded on 28 July 1981. Similar low maximums have been recorded in the Sydney region in winter. 9am humidity ranges from 61 % to 74% across the Sydney region, with the more higher figures experienced in June mornings. Highs of , whilst rare, are not unheard of in winter. Sydney receives around 15 days of fog annually, which occurs in winter mornings, but more often in June when moist easterlies dominate. The inland suburbs would generally receive radiation fog thanks to nocturnal cooling under a clear sky of humid maritime air that was brought inland by the previous day's sea breeze. The coastal suburbs would mostly get an advective fog, which floats ashore from the meeting of warm water offshore and cold water  nearby on the land. Heavier rain and cloudiness are also to be expected more in June, on average, than the latter winter months. During late winter, warm dry westerly winds which dominate may raise the maximum temperatures as high as in some instances. As the subtropical ridge is north of Sydney in mid-late winter, it picks up dry westerlies from the continent's interior because of its anticlockwise rotation, thus producing more sunny days in the region, hence why August has the highest sunshine percentage than any other month. In early winter, the UV index averages at 2, which  means it's safe to be outdoors unprotected, but it reaches 3 by the end of the season (therefore sun protection is required for the general population). The lowest recorded minimum at Observatory Hill was on 22 June 1932, while the coldest in the Sydney metropolitan area was , in Richmond. The lowest recorded maximum temperature at Observatory Hill was . Although not usually considered a suburb of Sydney, Picton, a town in the Macarthur Region of Sydney, recorded a low of on 16 July 1970. Spring. Early spring is rapidly transitional. Cool conditions from late winter may continue in September with  the maximum temperature dipping as low as at the coldest, but due to the drastic transition, temperatures above can also be expected in that month. By November, summery conditions begin, with temperatures normally ranging between and as high as , albeit with relatively low humidity. Because the subtropical ridge lies to the north of Sydney this time of the year, it will bring westerly winds from the interior that produce mostly sunny conditions, at times warm, with the temperatures averaging between and with relatively low dewpoints, hovering between and . Some days may be windy due to the dry westerlies and nights  may be relatively cool, where temperatures plummet down to around in some suburbs. Hot air from the interior that soar temperatures to over can be expected, especially in the months of October and November. These conditions are rare in September, but not unheard of. Extreme, changeable and inconsistent temperatures are much more prevalent in spring than other seasons. In some occasions, hot dry days are cooled down by a southerly buster, which eventually lower the temperatures from to as low as . Such extremes usually happen in mid-late spring. Other seasons seldom see such fluctuations in a day's span . Furthermore, the diurnal range is higher in this season than it is in autumn. The lowest maximum temperature in spring was , recorded on 8 September 1869. 9am relative humidity is the lowest in the year during spring, ranging from 58% to 68%, with early spring receiving lower figures. Warm and cool periods. The Bureau of Meteorology reported in 2011 that 2002 to 2005 had been the warmest years in Sydney since records began in 1859. 2004 saw an average daily maximum temperature of , 2005 of , 2002 of , and 2003 of . The average daily maximum between 1859 and 2004 was  . Seven (of the ten) warmest years in 151 years of recordkeeping have occurred in the ten years between 2001 and 2010, with this decade being the warmest on record for minimum temperatures. The Bureau of Meteorology reported that the summer of 2007–08 was the coolest in 11 years, the wettest in six years, the cloudiest in 16 years, and one of only three summers in recorded history to lack a maximum temperature above . The Bureau of Meteorology reported that 2009 was a warm year. The average annual daytime temperature at Observatory Hill was , which is above the historical annual average . This ranks as the seventh highest annual average maximum temperature since records commenced in 1859. 2010 was the equal fourth warmest year on record for Sydney, with an average maximum of , which was above the historical annual average. In 2013, the city had the warmest July and September on record, with September being one of the driest. In September, temperatures were above average and the city had over seven days where temperatures reached , making it more similar to November's weather pattern. October 2015 had the warmest nights on record, which were above average. The warming trend continued in 2016  as Sydney's warmest autumn ever was recorded. July 2017 to June 2018 in southeastern Australia proved to be the hottest financial year on record with maximum temperatures being the warmest on record and minimums above average. Sydney experienced its hottest summer since records began in the summer of 2016–17, with more than 10 days over . Sydney's 2017 mean temperature of degrees was degrees above the long term average and the second highest value in 158 years of records. The warmest year on record was 2016, with a mean temperature of degrees. On 7 January 2018, Sydney was the  hottest place on Earth. In April 2018, Sydney had the longest running hot spell for that month with nine consecutive days of temperatures reaching . Furthermore, the airport and parts of the western suburbs also broke heat records in that month. The 2020-21 summer was the coolest in a decade due to La Nina's influence. During May 2021, Sydney CBD recorded its coldest stretch of May days in 54 years due to a polar blast that swept across Australia's southeast, which kept the temperatures below in the early mornings for five consecutive nights, in addition to the inland  suburbs dipping down to and . On June 10, 2021, Sydney CBD had its coldest day since 1984 and the coldest June day since 1899, where it reached a maximum of just . Bankstown, a western suburb, only reached , its coldest day in 50 years, with nearby suburbs registering a similar temperature. These unusually cold maximums were caused by a cut-off low, which is a slow moving, sizeable Antarctic cold air mass that got "cut-off" from the westerly trough systems of cold air in the south where it reached the east coast. August 2021 registered 15 consecutive winter days above  , the first time in 163 years of records, which was achieved due to a lack of cold fronts or rain over NSW during the month and a blocking high in Southern Australia that prevented cold fronts from reaching the continent. Microclimate. The region of Sydney is subject to phenomena typical of a microclimate, namely in late spring and summer, where the western suburbs would be hotter than the Sydney CBD by due to urban sprawl exacerbating the urban heat island effect and less exposure to mitigating sea breezes which cool down Sydney's eastern edge and would fail to move  inland. The dramatic temperature difference between coastal and inland areas is caused by a combination of desert-warmed air from central Australia reaching the west, and as well as density of housing, lack of vegetation or open spaces, and the Blue Mountains which help trap the hot air. When it is at Bondi for instance, the temperature will be around just west of the Sydney Harbour Bridge, around near Parramatta and as much as inland. Such extreme temperature differences in the Sydney metropolitan area usually occur in late spring when the western Pacific Ocean is still quite cool and the  inland air is warm. Furthermore, within the CBD, heat maps show the area around Central Station (in Haymarket) is warmer than Circular Quay and surrounds, making it the hottest place in the CBD. According to ecologist, Dr Sebastian Pfautsch from the University of Freiburg, in Sydney's hot days there could be discrepancies of up to 22 more days above recorded in urban space compared to a weather station from the Bureau of Meteorology. Because was recorded in Penrith (on 4 January 2020), it won't be unusual to have a reading somewhere nearby, especially if it lacked green space  and retained heat to intensify heatwave temperatures. Moreover, a heat logger registered a temperature of at Berkshire Park, making it the hottest temperature ever recorded in the Sydney basin, albeit being an unofficial one. Richmond has the second largest overall temperature range recorded in Australia, after Mitchell, Queensland; to . Urban heat island. A study by the University of Western Australia and RMIT indicated that the western suburbs have a much stronger urban heat island effect than those east of the CBD and that hotter temperatures in the west are human contributed due to solar radiation absorbing materials in black asphalt  and dark roofs, anthropogenic heat from cars and less natural environments, thereby creating a "heat dome" that blocks the cooler air from the sea. Greening Australia stated that January mean maximum temperatures in the west have risen at a pace of 0.65 °C per decade, over twice as much as eastern Sydney's 0.28 °C per decade. The OEH warned that further development could cause more exceedingly hot days in the west by 2030. Annually, coastal Sydney sees five heat-related deaths per 100,000 people while the western suburbs see 14 per 100,000. Urban heat island of the  CBD has been efficaciously blocking the cooler air from reaching the inland suburbs because the CBD's "high temperature, is like a wall that stops the sea breeze in its tracks. Over Sydney’s CBD is a heat dome because of the high density of concrete and asphalt. If we want to cool western Sydney and demolish this wall, we need to cool the CBD first", Professor Mattheos Santamouris from UNSW states. He explained that cooling the CBD would reduce the temperature by 1.5 °C in the west and tree coverage could cool down suburban streets by as much  as in hot days since high-density housing developments and scarce trees trap heat. Waterbodies and open spaces also provide cooling benefits in urban areas. According to climate researchers, relatively easy modifications such as constructing fountains and water playgrounds could also lower temperatures in the western suburbs. The city now has 3.6% more trees in 2016 than it did in 2009 and Penrith City Council had planned to plant 100,000 trees from August 2018, in addition to planning a large city park, creating a water-sensitive urban design, street shading, and the use of cool materials in its building developments . Furthermore, Parramatta City Council has installed 20 temperature sensors among different tree species in its suburbs to compare how different species can help reduce urban heat. Precipitation. Rainfall seasonality. Rainfall is slightly higher or dominant during the first half of the year, particularly in late summer and early autumn, when the ocean has peaked its warmth. At this time of the year, the subtropical ridge is to the south of the continent, thereby directing easterly winds towards the east coast. Rainfall will tend to be lower in the second half of the year when the subtropical ridge is just to  the north of the city where it picks up dry winds from the continent's interior towards Sydney (as it rotates counter-clockwise) and this will be when clockwise-rotating low pressure systems are to the south of the continent. Due to the unpredictability of rain, the wettest and driest months would change on a yearly basis. The "wet" and "dry season" is more pronounced in the inland suburbs with late winter to early spring (August–September) having a drying trend and late summer to early autumn being wetter and greener (February–March). The drier winters are owed to its  rain shadow position on the leeward (eastern) side of the Great Dividing Range, which shield the region from south-westerly cold fronts that arrive from the Southern Ocean. Though east coast lows, which strike from the southeast in the Tasman Sea, would provide heavy rainfall typically in late autumn and early winter with Sydney CBD being heavily impacted due to its location on the coast. Other rainfall drivers include Black nor'easters (in the warm months), upper-level lows (all year round) and Australian northwest cloudbands (all year round) and as well as, albeit rarely, tropical cyclone remnants. The annual evaporation  rate for Sydney is , with the rate in the summer being and in winter . Rainfall amount. Within the city and surrounds, rainfall varies, from around at Badgerys Creek (in the west) to at Turramurra (the northeast) in the Northern Suburbs, which create an orographic rainfall. Even in its months of highest rainfall, Sydney has relatively few rainy days, with an average mean of 7 to 8 rainy days per month on the threshold, despite having a moderate to high amount of annual rainfall at around to (depending on the area) – This illustrates that Sydney generally receives short-lived, heavy rainfall  day events, usually not lasting more than 2 or 3 days, which give away to mostly propitious conditions for many weeks to months even, especially during an El Niño period (though during a La Niña event, rainfall may be intermittent for many days or weeks). In some days, rain may come in drizzle form, though this is rare as most rain comes mostly from major storms. In the warm months, rain comes in short heavy downpours in the afternoons, usually cooling the conditions and providing some respite. Sometimes these afternoon showers give away to the sun again, although black nor'easters  may provide rainfall for a few consecutive days. In 2022, Sydney recorded its wettest March on record with the rain gauge picking up of rain, beating from 1942 – this also brought Sydney's annual total up to , which is the highest January-to-March total in records that date back to 1859. The high amount of rainfall was caused by a combination of the La Nina phase, an anomalously warm Tasman Sea, and a consistently positive Southern Annular Mode (SAM). In April that year, Sydney CBD exceeded its long-term annual average rainfall of , which set a new record for  the fastest time to accumulate a year’s worth of rain in the CBD. This surpassed the previous record by a month – The old record was May 6 in 1890 and the following record was May 3 in 1990. Storms. Sydney experiences east coast lows, which tend strike in the cool season (but can occur any time of the year), usually during a positive SAM phase. The precipitation of the low comes from a nimbostratus cloud that would dump as much as of rain for as much as two days, though when the cloud is thick enough 100mm of  rain can fall in three hours as was the rare case in August 1986. Due to onshore winds, the CBD would be susceptible to some light rain and drizzle – These conditions usually don't penetrate the inland suburbs. However, the western suburbs are more inclined to receive thunderstorms in summer due to the stabilizing effect of a sea breeze in the afternoon near the CBD and Eastern Suburbs, however the stabilizing effect does not always occur as was the case during the 1947 event as according to Newmans report there was a sea breeze on the day it occurred.. The  city is rarely affected by cyclones, although remnants of ex-cyclones do affect the city. The city is prone to severe hail storms, such as the 1947 Sydney hailstorm, wind storms, and flash flooding from rain caused either by East Coast Lows (such as the major storm in early June 2007) or ex-tropical cyclone remnants. Scientists have predicted that rainfall will become more unpredictable and temperatures will be on the rise. Parts of western Sydney were substantially flooded during the New South Wales 2021 floods, with many areas around Richmond and Windsor submerged in floodwaters. In early 2022, Sydney  recorded its wettest start to a year on record with the running annual total being , topping to the same date in 1956 and in 1990, respectively (rainfall data at Sydney Observatory Hill dates back to 1858). Snowfall. Snow is extremely rare in Sydney, with significant snowfall being last reported in the Sydney area on 28 June 1836. On that date, it was reported that convicts and British settlers in Hyde Park woke up to snow "nearly an inch deep", with the meteorological table in The Sydney Herald recording that on the morning of the snow the temperature dropped to . The  snow event affected trading where sellers were unable to transport goods to markets in the colony. The snowfall occurred at the end of the dalton minimum, a solar cycle period representing low solar activity, where colder temperatures were recorded globally. A keeper of weather observations during that period, T. A. Browne noted: "The Sydney Morning Herald" reported on the event, saying: "The Sydney Monitor" reported: Scant snowfall has been recorded in latter dates: On 22 June 1951, light snowflakes (which melted into rain) were reported in the suburbs of Liverpool, Pymble and Kingsgrove. On 18 July 1965, very light snow  fell in Berowra Heights and Hornsby. On 21 June 1972, settling snow was allegedly observed in what is now Kellyville Ridge, although it may have been soft hail or ice pellets. On 25 July 1986, melting snow was observed in metropolitan Sydney, in addition to some settling snow being reported in North Ryde. On 27 July 2008, a fall of graupel or soft hail (which was mistaken for snow by residents), blanketed Lindfield, Roseville and Killara in white. Owing to this event, a senior forecaster from the Bureau of Meteorology doubted the 1836 snow account, stating that weather observers in  that time period lacked the technology and skill to distinguish snow from soft hail. Blue Mountains. The Blue Mountains, a temperate oceanic region bordering on Sydney's metropolitan area, have a reputation for snow in winter, with places such as Katoomba, Leura and Blackheath receiving the most snow due to their higher elevation. Despite the reputation, there are only around five snowy days per year in the upper mountains area with two settled falls per season, and another five to ten days of light snow showers or sleet. Settled snow has become less common in recent decades. It is extremely  rare to see snow below Lawson. Drought. Sydney's climate appears to be becoming drier; The city has had fewer rain days in recent years than shown in the long-term climate table above. In summer, Sydney can go for long periods without rainfall. The other phenomenon that arises from these long, dry and hot periods is bushfires, which occur frequently in the areas surrounding the city. Water supply is a recurring concern for the city during drought periods. In 2005 the reservoirs reached an all-time low. However, water levels since then have recovered in 2013. 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. Heatwaves, which are regularly occurring in recent years, would usually lead to water restrictions and a high risk of bushfires, which sometimes bring a smoky haze to the city. Smog is noticeable on hot days, even without bushfires. The years 2009 and 2010 had dry conditions, according to Bureau of Meteorology. On 23 September 2009, a dust storm that started in South Australia and inland New South Wales blanketed the city with reddish orange skies early in the morning . Originating from the north-eastern region of South Australia, the dust storm lifted thousands of tons of dirt and soil which were then dumped in Sydney Harbour and the Tasman Sea. It stretched as far north as southern Queensland and it was the worst dust storm in 70 years. During that year, Sydney experienced a number of warm winter days, dry gusty winds and another milder dust storm. In 2011, Sydney had the driest February in 30 years with only of rain falling, which is well below the average of . Some of the western suburbs recorded the lowest total February  rainfall on record. In September 2013, the combination of dry weather, warm temperatures and strong winds brought early-season bushfires. Major bushfires impacted western Sydney and the Blue Mountains, resulting in some evacuations, closed roads, and destroyed homes. The summer of 2013-14 was the driest in 72 years. The precipitation of December 2013 and January 2014, inclusively, only added up to , which is only a quarter of a typical amount for December and January. Observatory Hill only received of rain in January. September 2017 was the driest on record, with the gauge receiving only of rain. Furthermore, in that  year, the city received less than half of its long-term average rainfall between July and December. In the late morning and early lunchtime of 22 November 2018, a dust storm, stretching about 500 kilometres, swept through Sydney due to a low pressure trough and cold front that picked up dry soil in drought-ridden areas of far western NSW that week. Milder compared to the 2009 storm, the effect of the dust was still apparent across iconic locations such as the Sydney Opera House and Sydney Harbour Bridge. Furthermore, 2018 in Sydney has been one of the driest in  a century, with the Greater Western Sydney farming region being the worst affected. Due to the widespread bushfires in December 2019, which even affected the western periphery of the city, the Sydney metropolitan area suffered from dangerous smoky haze for several days throughout the month, with the air quality being 11 times the hazardous level in some days, even making it worse than New Delhi's, where it was also equalled to "smoking 32 cigarettes." 2019 was one of Sydney's warmest in 161 years and the driest since 2005, which had a few days of raised dust and as  well as declining dam levels. Rainfall in December was just 1.6 millimetres at Observatory Hill, overthrowing the record low of 2.8 millimetres recorded for the month in 1979. Wind. Averaging at , November is the windiest month, whilst March is the calmest at in the CBD. Some suburbs in the metropolitan area tend to be the windiest in January, September, October or December, and calmest in the months of May or June. As a whole, the Sydney region is generally the windiest from October to January and calmest from March to June. The more windier locations are those by the coast , such as the eastern suburbs. The prevailing wind annually is northeasterly. In the warm months, only 40% of the time Sydney would get wind directions from the northwest or southwest, which are the dry winds flown from the heated interior of Australia. Northeasterlies and easterly sea breezes are dominant from early summer to early autumn, because the anticlockwise-rotating subtropical ridge is to the south of the city where it allows winds from the sea to penetrate. Westerlies are dominant in late winter to mid-spring as the subtropical ridge is just to the north of the city, picking up  winds from the interior and blocking easterlies from the sea. Southerly busters are expected from October to the end of March. They typically look like as if a sheet of cloud is rolled up like a scroll by the advancing wind. The change of wind (in the warm months) is sometimes very sudden, where it may be fresh northeasterly and in ten minutes a southerly gale. Katabatic winds are light, south-westerly drainage winds, akin to land breezes, that occur when air of higher density in the Blue Mountains descends under gravity force into the Sydney metropolitan area and the  Hawkesbury Basin, usually during a winter night. Föhn effect. Since Sydney straddles the Great Dividing Range's eastern side, and thus falls on its rain shadow, it would experience a föhn-like type of wind, particularly between late autumn and spring, which is a dry south-westerly that raises the air temperature and provide clear to partly cloudy conditions in the lee of the mountains (in this case, the Sydney Basin). During the phenomena, atmospheric moisture is reduced due to the partial orographic obstruction of comparatively damp low-level air and the subsiding of drier upper-level air in leeward  of the mountains. In the cool season, these föhn-like winds can be particularly damaging to homes and would affect flights, in addition to being uncomfortable, as the wind chill factor would usually make the temperatures feel cooler than what they are. Conversely, the foehn effect is one the few reasons why Sydney and other places in the coastal plain register high temperatures in the warm season but seldom attain cold maximum temperatures in the winter, and also the reason why late winter and early spring have the most amount of clear days in the year, as the Great Dividing  Range shelters the region from vigorous westerly cold fronts that arrive from the Southern Ocean. On 23 August 2012, a foehn effect caused Sydney to record its 3rd warmest August day on record where it reached at the CBD and at Sydney Airport. Historical season descriptions. Aboriginal. The Sydney Basin was in the Tharawal country. Each clan had knowledge of their area and the season changes. These were the seasons of the Sydney region according to the Aboriginal people living there: British. In 1819, British explorer William Wentworth described Sydney's climate as: Below, Wentworth describes Sydney's seasonal and  annual weather patterns in analytical detail: