The forecast Saturday scorcher arrived in Sydney, with Sydney Airport recording its hottest December day on record (in records going back to 1929).

• Sydney Airport's peak of 43.5°C just after 1 pm beat the old mark of 43.2°C which had stood since 1994.
• Sydney's official weather station at Observatory Hill, near the southern pylon of the Sydney Harbour Bridge, reached exactly 40°C as forecast just before 12:30 pm before the sea breeze kicked in.

Several locations in the city's outer west got hotter than Sydney Airport, including the site of Sydney's future second major airport at Badgerys Creek, which reached 44.0°C.

Despite the extreme heat in the outer west, as we write this story late on Saturday afternoon, it appears that December heat records in the western half of Sydney have been threatened but not quite broken. Up to 5 pm Saturday:

• Richmond in the northwest had reached 43.8°C
• Penrith in the far west had reached 43.9°C
• Badgerys Creek in the west had reached 44.0°C
• Holsworthy in the southwest had reached 43.8°C

As Weatherzone meteorologist Ben Domensino wrote on Friday, a cool change will flush the heat out of the Sydney Basin late on Saturday, bringing a brief period of relief into next week before another likely hot burst arrives midweek.

Meanwhile in Adelaide, it has been a totally different story this Saturday, as unseasonably heavy rain and southerly winds combined to keep temperatures below 16 degrees all the way from 9 am through to 4 pm.

• Adelaide's coldest December day on record saw a maximum of just 15.4°C back in 1955
• It's not yet clear where this Saturday sits in the pecking order of cold December Adelaide days (as official maximums aren’t available until 9 am the following day) but it may well end up being the coldest in 57 years.
• A total of 22 mm of rain fell in Adelaide from 9 am to 4 pm, on top of 8 mm of overnight rain which was already in the gauge at 9 am this morning - making it the wettest December day in seven years.

The loop above shows the constant feed of rain across parts of southern SA in a three-hour loop on Saturday afternoon.

Some areas have missed out while some areas in both SA and Victoria have copped a very welcome December drenching.

The image below shows the rain observations since 9 am, as well as the areas of heat and cool, in what was a hugely contrasting day of December weather in southeastern Australia.