Many recent conversations around Sydney have been about how much it has cooled this autumn, so we investigated and have found some numbers to back it up. 

These conversations have been warranted. In just 60 days, the city has cooled by 10 degrees.

This turns out to be the biggest autumn cooling in 12 years, the second biggest autumn cooling in 55 years, and the fifth biggest autumn cooing in more than 160 years of records. 

The week ending Thursday 11th May had an average temperature of a chilly 14.7 degrees, compared to a balmy 24.7 degrees in the week ending 12th March. 

For some, particularly those with not-so-well-insulated homes, it's been a quick turnaround from air-conditioned cooling to heating, and from sheet to doona. Some rooms in these homes are likely to have cooled by a similar amount as it has outside. 

Typical 60-day cooling is between 5.5 and six degrees. This year's household energy usage has only had a brief lull, during April. 

This year's cooling has been largely due to the breakdown of La Nina and a few strong cold fronts. A winter-like cold front a week ago delivered as much as 10cm of snow as far north as the NSW Central Tablelands. 

Previous years with more autumn cooling were 2011 (10.4 degrees in 60 days), 1968 (10.5 degrees in 60 days, 1926 (10.7 degrees in 60 days), and 1861 (a record 10.9 degrees in 60 days). 

Looking ahead, cooling is expected to be nearer to normal due to the Southern Annular Mode (SAM) becoming more positive, meaning cold fronts have weakened and should stay relatively weak for a little while.