This exceeds the 18 days under zero which were recorded in May of 1959 and 1961. The record standing now is from 1957 which had 27 days with minimums under zero. Data at Canberra Airport station # 70014 starts in 1939.
I understand this is weather not climate but we all know how the BoM trumpets any warm record it can in the main stream media – so we will be interested to see what the BoM says after the month ends. And we must remember this cold record was set despite the ever increasing Canberra urban heat island.