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Heading for the coldest June in decades for the ACT and southeast NSW

June has been the coldest in decades over parts southeast Australia, particularly in the ACT and southeast NSW around the Southern Tablelands.  

The month started mild enough, then a vigorous cold front with a long-lasting low pressure system blasted the region over the King's birthday long weekend. Lingering high pressure cells and very dry air behind the front led to a run of nights that dropped into the severe frost territory, below -5°C. Then the pattern repeated, twice.  

Canberra and Cooma are leading the charge for the coldest stats. 

Canberra is on track for its coldest June in terms of minima since 1984, averaging just -2.5°C for the month so far. With forecasts below -3°C the next two nights, that statistic is unlikely to change. Every morning, bar seven of the 28 days of the month so far, has been below zero, with a coldest-in-decades run of three consecutive days below -7°C last week. Now, the capital is heading for another four consecutive nights under –5°C. Aside from last week, that hadn’t happened in any month since 2018.  

Days in Canberra have also been cold. It's more typical for cold nights to be accompanied by near or slightly above average days, but the frequent fronts and their lingering cold airmasses and daytime low cloud have prevented that this month. Maxima for Canberra this June so far are tracking around one degree below average at 12.3°C, making the combined average of minima and maxima for the month to date just over 5.0°C. That's the coldest for June since records began in 1939. By the end of Sunday, that title could just be pipped by 1960 or 1965, but it will still have been the coldest in decades.  

Image: Mostly clear skies combined with dry southwest to westerly winds behind cold fronts, like on this past Thursday, have contributed to the cold minima. Note the low cloud over alpine areas and some other areas that have helped keep the maxima down also.  

Another very cold place this month has been Cooma. Cooma Airport's average minima for the month so far has been -3.5°C, ranking as the coldest since at least 1991. That low average was helped by the drop to a frigid -8.5°C and -8.4°C on the mornings of the 20th and 21st, respectively. In terms of minima and maxima averaged together, Cooma is coming in at 3.3°C, putting it in the vicinity of the coldest since 2007, but this is hard to verify for certain given missing data on June 17th. 

Next up in the cold stakes is Goulburn, which is averaging 6.2°C in terms of minima and maxima for June so far—the coldest since at least 1977—but it could end up being warmer than 1982 by the time month is over. In terms of minima, Goulburn has not had extremes as cold as further west on the tablelands this June, thanks to plenty of low cloud. But it has been consistently cool, helping the average minima so far to be 0.7°C, two degrees below average. 

Other notable cold locations during June so far have been, 

• Moss Vale: average minima 0.6°C, -2.9°C below average and the coldest for June since at least 2000. 

• Nowra: average minima 6.3°C, -1.4°C below average and the coldest for June since at least 2006. 

• Campbelltown: average minima 3.6°C, -2.1°C below average and the coldest for June since at least 2008. 

With cool to cold nights forecast over the ACT and much of southeast NSW for the final two days of June, these numbers are unlikely to go up much.  

The cold has extended to alpine areas, with the best snow start to the season since 2022. 

From Monday, the string of very cool nights over eastern NSW will be over, at least for a while, with a humid easterly airstream wrapping around a deep low that is expected to develop offshore. However, it's likely to stay cold over the western tablelands and alps. Then further cold nights will follow for the east after the low moves away.  

 Image: Minimum temperature anomalies for the last week. Source: Bureau of Meteorology.