The interior of eastern Australia has had a run of below-average cool mornings, thanks to clear overnight skies that have persisted for quite some time.

As of Sunday morning 9am AEDT, places like Armidale, Orange, Williamtown and Canberra all reported minimum temperatures near sunrise between two and three degrees below average.

A number of places have consistently recorded minimum temperatures two to four degrees below the monthly average during the past week, especially over the slopes and tablelands of New South Wales. While elevated areas tend to be a bit cooler due to their height above sea level, clear overnight and early morning skies greatly enhance overnight cooling.

During the warming hours of the day, radiation from the sun gradually heats the surface of the earth. After the peak radiation near midday, its actually the surface of the earth that radiates this heat that heats the air closest to the surface. This accounts for why the maximum temperature generally only occurs in the afternoons, a few hours after the solar radiation maximum. When skies are clear overnight, it allows for heat to escape rapidly and more extensively, bringing usually cooler mornings.

A cold front is set to sweep over the southeastern parts of the country early next week. While this will bring a few hot days, its likely that evenings remain cooler into the start of the week as skies remain relatively clear.