This time of year is notable for its big weather swings and this week is no exception with some places in the south of the country expected to cool by as much as 15-20 degrees in 24 hours.

This week's change promises to turn southern Australia into winter only a day after enjoying some warmth. Temperatures will reach five-to-10 degrees above average then dip just as much below average in a day.

The areas likely to cool the most in a hurry include Eucla in Western Australia and Whyalla in South Australia. Eucla reached 38.8 degrees on Saturday afternoon (17 degrees above average and a 58-year high for September) and should cool below 18 degrees during Sunday afternoon. Whyalla should reach about 34 degrees on Sunday before cooling to about 16 degrees later in the day, including a 10-degree drop in about an hour.

Cooling of 15-17 degrees is likely further east in the next few days, including Victoria's Mildura and New South Wales' Mudgee, Cessnock and Dubbo and parts of Sydney.

Temperature swings such as this are typical for this time of year as summer-like weather systems develop and try to fight off lingering winter-like systems.

This week's change will also bring rain to some areas, most widespread in Victoria, the ACT and NSW.