AUSTRALIA'S ''dome of heat'' is becoming so intense, temperatures are off the charts - literally.
When the weather bureau's model started churning out predictions for next Sunday and Monday of more than 50 degrees, chart producers quietly extended the scale beyond the level previously used.
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For now, those days show regions of South Australia with deep purple - indicating 50-52 degrees. As yet, the new maximum scale of 52-54 degrees - to be coloured pink - does not feature.
"It's because we've been going off the scale," said David Jones, head of the bureau's climate monitoring and prediction unit.
Also off the scale was the national average maximum. It hit 40.33 degrees on Monday, a record that has stood for 40 years but was likely to be broken on Tuesday, the bureau said.
Including Tuesday, the country will have posted four of the hottest 10 days on record in 2013 - a year barely a week old.
Another record that was smashed on Monday was Australia's mean temperature. The country averaged 32.23, eclipsing the previous record - set on December 21, 1972 - of 31.86 degrees.
The temperature at Observatory Hill hit 42.3 degrees, its hottest since New Year's Day 2006 and the fifth hottest day since records began in 1858.
After a brief respite, the heat may return by the week's end. "Another hot air mass is moving in on Friday and Saturday," said Ben McBurney, of Weatherzone. "It's potentially going to be hotter than this one."
Forecasters say the weak northern monsoon and absence of strong cold fronts moving across the south of the continent mean there is little to break up the giant heat cell.
So far, one of the country's longest-standing records is unchallenged - the 50.7 degrees at Oodnadatta Airport on January 2, 1960. But even that peak is under threat as the heat looks likely to re-intensify in coming days.
"We're setting up to have a go at that record," said Karl Braganza, the bureau's manager of climate monitoring. "On Monday we might have a shot at it."
Even if the Oodnadatta record stands, many towns are sweltering. Birdsville in central western Queensland had had a week of 45 degree maximums and might make it to a fortnight, said Brett Dutschke, senior meteorologist at Weatherzone.
Bourke in north-western NSW has averaged 42.5 degree maximums in the past week and faces another week of scorching temperatures.
A few thunderstorms were expected in western NSW late on Tuesday and to reach northern regions on Wednesday. These might be ''more hazardous than beneficial'' because of the potential for lightning and gusting winds adding to the fire risks, he said. More rainfall may come over the weekend and next week.