Adelaide's 15-day heatwave was a once in 3,000 year occurrence, an atmospheric scientist says.

Adelaide has sweltered through 15 consecutive days above 35 degrees - the longest heatwave recorded in any Australian capital city.

The heatwave ended on Tuesday, with a milder 29 degrees maximum forecast.

Atmospheric scientist Warwick Grace said the 15-day heatwave had a .03 per cent of occurring.

"The odds are about the same as tossing 12 coins and getting all heads or all tails," Dr Grace said on Tuesday.

Dr Grace has been working with the South Australian Research and Development Institute (SARDI) Climate Applications Unit to gain a better understanding of heatwaves in wine growing regions of the state.

He has developed what is believed to be the first heatwave occurrence model, based on statewide dating back more than 100 years, and statistics from the past 30 years collected at the Bureau of Meteorology at Kent Town in Adelaide.

"This heat wave is close to being off the scale," he said.

"Adelaide, with 15 days over 35 degrees, returns a one in 3,000 year event."

Dr Grace said Nuriootpa, in the Barossa Valley, recorded 13 days over 35 degrees - a one in 1,000 year event, while Loxton in the state's Riverland had 15 days over 35 degrees which was a one in 200 year event.

Adelaide's 15-day heatwave surpassed the previous capital city heatwave record of Perth, which experienced 10 days over 35 degrees in February 1988.

The all-time national heatwave record was set in Marble Bar in northern Western Australia, which had 160 consecutive days at or above 37.8 degrees celsius (or 100 degrees fahrenheit) in the summer of 1923-24.