Did Sydney just have a January or a July weekend? If you glanced quickly at the maximum temperatures, you'd surely guess that it was summer.

Sunday was particularly warm, with parts of the city exceeding 26°C during what is normally the coldest month of the year.

The city (Observatory Hill) reached 25.2°C, which was:

• Almost nine degrees above the long-term July average max of 16.4°C
• Within a degree of the long-term January average max of 26.0°C, and bear in mind that January is on average the hottest month

Sydney Airport reached 26.0°C which was:

• Almost nine degrees above the long-term July average max of 17.2°C
• Within a degree of the long-term January average max of 26.7°C, and bear in mind that January is on average the hottest month

Penrith, in the city's outer west, reached 26.4°C which was:

• More than eight degrees above the July average max of 18.0°C
• Within 4.5°C of the average max of 30.9°C in January, which again, is on average the hottest month
• Penrith also registered Sunday’s equal fourth-warmest NSW reading, with the warmest being 27.5°C at Grafton in the state's Northern Rivers forecast district.

Why so warm in midwinter?

Warm northwesterlies were pushed across southeastern Australia on Sunday by a low pressure system down near Tasmania.

If you look at Sunday's live temps at 2 pm, you can see how cooler air had reached areas west of the divide, while anywhere along the east coast was super warm for midwinter.

Indeed warm temps were being experienced all the way down to East Gippsland in Victoria at the very bottom of the image, where towns like Orbost at the mouth of the Snowy River got a rare winter taste of 21-degree weather

Meanwhile Monday is looming as a dry but slightly cooler day in most of the hotspots mentioned above, although it will hardly be cold by winter standards.

Sydney should see maximums of at least 20°C for at least the rest of the week, while Canberra will also continue its run of much warmer maximum temps than usual for winter.