One of established Canberrans' greatest joys at this time of the year is to tell horrified newcomers of the "Anzac Day rule" for heating.
To use a heater, fire or electric blanket before April 25 is a sign of weakness, the rule decreed, as the public holiday marks the true start of the wintry weather that will only ease up in mid-spring.
As a relief to the new settlers who had already succumbed to indoor heating, however, long-term climate data shows the arbitrary marker of the cold season is often warmer than the days that precede it.
According to 78 years of Bureau of Meteorology data, between January 1 and April 25, there were on average 19 days with lower minimum temperatures and 13 days with lower maximum temperatures than Anzac Day.
Between 1939 and 2017, April 24 had colder maximum temperatures than April 25 in 44 of the years and colder minimums in 42.
In those years, a total of 62 days between the start of the year and Anzac Day had temperatures below zero.
Bureau of Meteorology climatologist Joel Lisonbee said although cold snaps earlier in the year were possible, they became more frequent from the end of April and beginning of May.
He said cold fronts restricted to Victoria and Tasmania during summer moved northward during that time, buoyed by air pushed from the Antarctic toward the top of Australia.
"There isn't an exact date, but generally by the end of April you have transitioning patterns from the virtual summer conditions to winter weather," he said.
ActewAGL figures from the past three years suggested Canberrans reliant on gas for warmth were more likely to hold out on heating until the end of April.
ActewAGL works delivery branch manager Clinton McAlister said gas use increased by 25 to 35 per cent in the week after Anzac Day, compared to the week before.
But he said electricity use generally rose from the end of March onwards, before it hit the winter peak between mid and late July.
"The Anzac Day rule appears to apply more for gas use than electricity use," Mr McAlister said.
The "rule" is not unique to Canberra, having been mentioned in towns ranging from those bordering the ACT to at least as far north as Armidale.
A Canberra Times editorial from 1980 described Anzac Day as a "seasonal watershed" after which "we start reaching for those thicker pullovers, topcoats and gloves as the cold begins to bite".
Liz Gailer first heard about it when she moved to Yass 31 years ago, but she said she was not a strict adherent to the rule.
"I had the air conditioning on a couple of weeks ago and I've had the electric blanket on for about two weeks as well," she said.
"It's a good thing to try and keep to, but hey, if it's freezing, I'm not going to sit there shivering."