Canberra is forecast to break a 67-year-old record for a late-autumn heatwave on Thursday, when temperatures are expected to pass 17 degrees for the 11th consecutive day.
The ACT region has had nine days with temperatures at least three degrees above the monthly average, and could be set for more than 12 by the end of the week.
Weatherzone meteorologist Max Gonzalez said the last time Canberra had experienced such a late autumn heatwave was in 1947, when temperatures passed 17 degrees for 11 days leading to May 21.
He said while the daytime temperatures in Canberra had been above average, the city had also been experiencing colder than usual nights.
"The average overnight temperature in Canberra this month has been 1.5 degrees which is 1.6 below the usual average," he said.
"But during the day we’re averaging temperatures of 16.8 which is 1.2 degrees warmer than the monthly average."
Mr Gonzalez said only 3.8mm of rainfall has been recorded in Canberra this month. This was significantly less than the 43.3mm average for May.
"At the moment we’re seeing some light rain fall just south of Canberra moving east with some cloud cover over New South Wales, although this is only likely to bring 1-2mm of rain," he said.
"We had a light trace of showers last Thursday although before that the last significant rainfall was 2mm recorded on May 4," he said.
The relatively dry May is a contrast to the early weeks of autumn, when Canberra exceeded the average autumn rainfall of 141mm in just six weeks.
But Mr Gonzales said Canberra might experience more rain on Friday, when a potential 5mm was forecast. Temperatures are expected to remain high on the weekend, with a top of 19 degrees on Saturday and Sunday.
"A cold front moving across Canberra late on Thursday on Friday may bring rainfall to Canberra for the first time in weeks," he said.
Mr Gonzales said next week should be slightly cooler, although temperatures should remain around or above the average daytime temperature of 15.6 degrees.
Meterologist Ben McBurney said the "18-20 degree mark everyday in Canberra" over the past week was "definitely a fair bit warmer than usual".
"We've only seen two strong cold fronts move through the east in the last month, so that'll mean conditions are generally less windy than they would be at this time of year," he said.
Mr McBurney said the unusually warm temperatures were due to a high pressure system off the NSW coast which had been affecting the region for the past few weeks.
He said the high pressure system had also been keeping winds low, meaning clear, bright days for the Canberra region but also a number of cool nights.
"The winds have been very light, no dominant winds at all, making for very pleasant days," he said.
Mr Gonzalez said it was likely alpine resorts could be waiting for weeks until snow began to fall on snowfields.
The warm weather has also caused blue-green algae blooms that have forced the closure of Lake Burley Griffin and Lake Tuggeranong.