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BAMOS August 2025
Charts of the Past with Blair Trewin 11 July, 1971
Prolonged periods of inland frost associated with blocking anticyclones are a common feature of the southern Australian winter. Two notable winters in this respect were those of 1970 and 1971. In July 1970, the most abnormal cold occurred in a region extending from central New South Wales to southern Queensland. In July 1971, it was mostly focused on central and southern New South Wales.
The most extreme low temperatures occurred in the second week of July 1971 as a blocking anticyclone dominated southern Australia. A weak front crossed Victoria and Tasmania on the 9th, producing very little rain outside of southern Victoria but injecting colder and drier air into the existing air mass over New South Wales. With dry conditions and low soil moisture( Canberra received only 2.3 mm of rain from 3 June to 14 July), the situation was ideal for extremely low minimum temperatures during this period.
The coldest nights occurred on 11 and 12 July. Gudgenby, which lies at 975 m elevation in what is now Namadgi National Park south of Canberra, set an ACT record with −14.6 ° C on 11 July, and Goulburn Airport( 641 m) reached −13.8 ° C that day and −13.9 ° C the next day. Both are the lowest temperatures ever recorded in Australia at such low elevations.
Canberra Airport set its lowest temperature on record with −10.0 ° C on the 11th. This was part of a series of records, with three consecutive nights below −8 ° C and four consecutive nights below −7 ° C. Other records included −11.2 ° C at Bowral on the 11th, and −8.8 ° C and −8.7 ° C at Molong and Yass, respectively, on the 12th. Bathurst reached −8.9 ° C on the 12th, a July record and its lowest since June 1927. This record occurred during a sequence of cold nights, with an average of −6.2 ° C between 1 and 13 July.
Reported impacts were modest, mostly involving frozen or burst water pipes. Some frost damage to crops was reported in southern Queensland, and classes were disrupted in a Canberra school when teachers refused to work in classrooms with temperatures below 10 ° C. Ice was reported on the Molonglo River near Queanbeyan and the Mulwaree River at Goulburn.
Daytime temperatures were near average during this period. For example, Canberra ' s maximum on 11 July was 11.2 ° C, very close to its July average. Alpine areas were cold but well above record levels, with Charlotte Pass ' s lowest temperature during the period being −12.8 ° C. Some notable low minimum temperatures occurred in near-coastal areas( for example, −6.4 ° C at Bega and −3.8 ° C at Richmond) and in northern New South Wales( −10.6 ° C at Walcha, −10.3 ° C at Woolbrook), as well as in southern Queensland.
However, it was generally warmer in those areas than during the 1970 event. Long sequences of frosts, such as 24 consecutive nights below 0 ° C at Inverell from 20 June to 13 July, were also mostly shorter than those in 1970. A record was broken at Wagga Wagga, with 14 consecutive nights below 0 ° C between 30 June and 13 July. There were widespread but mostly less severe frosts in Victoria, Tasmania and South Australia, as well as in the southern interior of Western Australia.
With anticyclonic conditions dominating the country, very little rain fell anywhere on the 11th, with light falls mostly confined to western Tasmania and the southwest coast of Victoria. An upper-level trough did, however, develop the next day and brought unseasonable light to moderate falls to the central Northern Territory and western Queensland. This marked the end of a very dry period nationally( the national average for 1−13 July was only 1.42 mm) with a pattern shift from midmonth.
Synoptic chart for 0000 UTC, 11 July 1971