Australia's ''dome of heat'' is becoming so intense, temperatures are off the charts - literally.
When the nation's weather bureau 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.
It showed those days as deep purple in parts of South Australia - indicating 50-52 degrees Celsius. As yet, the new maximum scale of 52-54C - 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.
However, the zones of purple have since disappeared from forecast charts for the next few days.
Weather projections made more than a few days out are, by their nature, less reliable, said Aaron Coutts-Smith, NSW manager for climate services at the bureau.
The predictions, made yesterday, were "a little too emphatic", he said.
That's not to say Australia's massive heatwave is showing much sign of cresting.
The country posted a record average maximum on Monday of 40.33C and although the latest indications suggest yesterday's tally may have fallen short of setting a new peak, it will likely be among the top handful of hottest days on record.
Including Tuesday, the country will have posted four of the hottest 10 days on record in 2013 - a year barely a week old.
And while coastal areas, particularly in the south-east will see some relief to the extreme heat and fire conditions, the giant heat cell over central Australia has days to run.
"We're not anticipating any significant clearing of that hot air," Coutts-Smith said.
Forecasters expect Sunday and Monday to provide the next chance of 50C-plus - and for the possible appearance of that new purple shade to the country's observed weather charts, not just the forecast maps.
Ben McBurney, a meteorologist at Weatherzone, says outback towns ranging from Bourke and Cobar in NSW to Moomba, Oodnadatta and Marree in South Australia are all candidates.
"There's potential for Bourke to reach 48-49 degrees and may get to 50 degrees on Sunday or Monday," McBurney said, "which is quite scary when you think of it."
Another record that was smashed on Monday was Australia's mean temperature. The country averaged 32.23C, eclipsing the previous record - set on December 21, 1972 - of 31.86C.
The temperature at Sydney's Observatory Hill hit 42.3C, its hottest since New Year's Day 2006 and the fifth hottest day since records began in 1858.
So far, one of the country's longest-standing records is unchallenged - the 50.7C at Oodnadatta Airport, South Australia, on January 2, 1960. But even that peak is under threat with the heat likely to re-intensify in coming days.
- Sydney Morning Herald
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