The mercury dipped to 0.3 degrees Celsius overnight in Canberra, the coldest December temperature on record.
The record books were also re-written in Braidwood where the temperature dropped to minus 0.4 degrees and in Goulburn at minus 1.
There were also snowfalls on the Brindabella Range.
Sean Carson from the Bureau of Meteorology says it is Canberra's coldest December morning since record keeping began 75 years ago.
"To get that really cold night last night - the cold, really strong winds brought snow to the mountains yesterday and brought the cold air over us and just dropped out perfectly in time during the middle of the morning to allow that temperature to really plummet," he said.
Today's forecast is for sun and lights winds with a maximum temperature of 25 degrees.
© ABC 2012
13:25 EDT After a fairly cloudy morning, Sydney's skies are clearing nicely for a starry but cool night for Carols at the Domain.