A significant low-level snow event across eastern Australia
The period from 11 to 17 July 2015 saw a sequence of strong cold fronts affect eastern Australia. The most significant feature of this sequence was the occurrence of widespread snow outside of the Alpine region of southeastern Australia, extending along the Great Dividing Range from west of Sydney to the Granite Belt in southern Queensland. While few notable temperature extremes were observed during the period, the extent and depth of snow was remarkable by recent decades and resulted in disruptions at several major centres.
A sequence of cold fronts affects eastern Australia
After a mild start to winter 2015, the morning of 11 July saw the first of a sequence of strong cold fronts to affect eastern Australia (Figure 1). The first front brought early morning snow down to approximately 500 m in the ranges east of Adelaide and in the mid-north of South Australia. Light snow was reported as settling in the higher parts of the Mount Lofty ranges and further north around Hallett and Burra, and around Mount Remarkable in the southern Flinders Ranges.
Freezing levels (and snowlines) were relatively high further east on the 11th, but lowered during the day with the passage of the cold front. By the morning of the 12th, snow was reported to approximately 600 m in the ranges east of Melbourne, and to levels of 800 m to 1000 m in southern and central New South Wales including the Monaro Plains to the east of the Snowy Mountains. Although snowfall during this period was not significant in terms of elevation or depth, with most locations having similar snowfalls on multiple occasions in recent years, very light snow and/or sleet was reported as far north as the Granite Belt of Queensland during 12–13 July, most notably around the town of Eukey.
A more significant front crossed Victoria on the 14th with an associated cold pool moving into New South Wales on the 15th. Light snow fell in parts of central Victoria during the afternoon of the 14th, near Ballarat (500 m), Trentham (700 m), and the upper parts of the Dandenong Ranges (600 m). More widespread snow fell to low elevations in a belt from southwest Victoria to northeast Victoria on the morning of the 15th, with settling snow reported near Hamilton (250 m), Beechworth (560 m) and Stanley (800 m). For the most part snowfalls in Victoria were light and not significant by historical standards. (For example, the trace of snow reported in the Dandenong Ranges on the 14th compares to more than 10 cm which fell in August 2008.) The spatial extent of settling snow was modest in Victoria in comparison to events such as 25 July 1986.
The formation of a low pressure centre near the New South Wales coast on the 16th, with the passage of a deep upper-level low pressure trough near the New South Wales Central Tablelands, was the trigger for unusually heavy and widespread snow reported in central New South Wales and into southern Queensland. Daytime temperatures on the 16th were generally very much below average for central and western parts of New South Wales, with large areas experiencing daytime maximum temperatures 6 °C to 8 °C below average (Figure 2). As the cold air tracked further north into Queensland overnight on the 16th and into the morning of the 17th, snowfall was reported at many locations along the Great Dividing Range, extending from the Blue Mountains west of Sydney to as far north as Eukey (965 m) and Stanthorpe (811 m) in southeast Queensland.
In southern Queensland, sleet was reported at Eukey late on the 16th, turning to snow falling heavily at times early on the 17th. There were multiple reports of snow settling at elevations above 800 m in the Granite Belt, with accumulations around 5 cm in Stanthorpe and Eukey itself. There were reports of brief snow flurries as far north as Toowoomba on the morning of the 17th, consistent with temperatures near 0 °C at the time.
At the peak of the event, snow fell at many locations above 600 m from central New South Wales to southeast Queensland. Settling snow was mostly confined to elevations above 800 m, although snow on the ground was reported in the central west of New South Wales to elevations of (about) 400 m. Locations which observed settled snow include Blackheath, Oberon, Katoomba, Orange, Bathurst, Armidale and Guyra in New South Wales, and Eukey, Stanthorpe, Applethorpe and Glen Aplin in Queensland. Measured snow depths were typically in the range of 5 cm to 15 cm, with heavier falls at higher elevations such as the Oberon Plateau. Snow generally stopped falling by the middle of the day on the 17th, and melted quickly over the next few days as milder temperatures returned.
Historical context of the event
The significance of an event such as low-level snow can be measured by its impacts (e.g. extent of disruption) and also how it compares to historical events. For the most part, the reported impacts of the snow have been relatively minor in part due to the fact that the snow did not last long. Significant and widespread snow falling outside of alpine areas is relatively rare in Australia and generated significant interest.
While snow in southeast Queensland tends to occur in most years, settling snow is rather uncommon at the elevation of towns as illustrated by the fact that the snow accumulations around Stanthorpe were the heaviest to have occurred since 1984 (when falls in excess of 10 cm were widespread and settling snow fell in Toowoomba). From this perspective, the event is the most significant to affect the region in approximately 30 years. Reporting of snow depths in New South Wales outside of alpine areas is patchy, and only limited comparisons are possible with historical events.
In the Blue Mountains, heavy snow was last observed in October 2014, though the recent event produced somewhat more extensive snow and slightly greater snow depths. The July 1984 event saw particularly heavy and widespread snow observed from central New South Wales into southern Queensland. The extent of the cold outbreak in early July 1984 is highlighted by the fact that New South Wales recorded its coldest statewide average maximum temperature of just 8.4 °C on 3 July 1984, compared to 10.9 °C on 16 July 2015. Reported snow depths in areas such as southern Queensland and northern New South Wales were also significantly greater for the 1984 event than those recently observed; for example, snow depths in excess of 30 cm were common at higher elevations in the New England Tablelands, with reports of up to 100 cm in the mountains in southeast Queensland.
Despite the widespread reports of snow, and minimum temperatures being well below average, there were no observations of lowest minimum temperatures on record. However, daytime maximum temperatures were very much below average on the 16th across central parts of New South Wales, with several stations reporting their lowest maximum temperature for several years (Table 1).
|Site name||Site number||Lowest maximum temperature (°C)||Years of record|
|West Wyalong Airport AWS||50017||7||17|
|Cowra Airport AWS||65111||6||12|
|Campbelltown (Mount Annan)||68257||10.2||10|
Daily maximum temperatures across much of New South Wales were below the 3rd percentile on the 16th (Figure 3), indicating temperatures which might typically be seen once every few years.
Area averaged statewide temperatures were below the long-term average, though well short of records. The New South Wales statewide maximum temperature for the 16th was 10.9 °C, the coldest July day for the State since 9 July 1986 (10.1 °C), and the coldest day for any month since 19 June 2007 (10.6 °C).
Values in this statement were current at 31 July 2015, and subject to the Bureau’s quality control processes.
Product Code: IDCKGMTA00