It was a seriously mild night in Australia's eastern states, with warm temps persisting across a broad area through Wednesday as a surge of unseasonable winter warmth spreads eastwards.

• Overnight, Melbourne had a warmer minimum (13.7°C) than Sydney (12.1°C). That was Melbourne's warmest minimum in the first week of June 2023 – and more than seven degrees above the average June min of 6.9°C.

Across eastern Australia, many locations had their warmest June minimum in decades, including:

• Ballarat (Vic) where the low of 11.5°C was the warmest June night in 28 years
• Broken Hill (NSW) where the low of 16.3°C was also the warmest in 28 years
• Moomba (SA), where the low of 20.2°C was the highest June minimum in the site's 27 years of records. Its average June minimum is 7.2°C

The Moomba reading is interesting. It's not often you can say that any location in South Australia stays warmer than 20°C overnight in winter, as even outback SA towns that are scorching in summer can often see frosty nights in dry winter weather.

This morning's synoptic chart shows you why. This isn't too technical. The orange arrow shows how warm air from the tropical north is currently being funnelled southwards across Australia's interior. Strong overnight winds helped prevent a nocturnal cooling effect at ground level.

For now, the aforementioned weather station at Moomba remains under the influence of that warm air, with a temperature of 28.1°C reached at 11 am Wednesday. Meanwhile the state capital Adelaide has also topped 20°C.

But the warm temps won't last too much longer, as a cold front and associated troughs push cooler air and showers across the southeast.

This won't be the most biting cold front of winter, with the coldest air sliding southeast into the Bight after peaking in southwest WA. But temps will still drop appreciably over coming days.

Showers and cloudy skies will also help cool things down, even where the unseasonably warm airmass persists. Cooler air is not due in Melbourne till later on Thursday into Friday, and while Wednesday started warm (for June) with the mercury topping 18°C just after 11 am, today's temp is unlikely to rise beyond that level as a rainband arrives.

Meanwhile Perth could be the capital city with the coldest maximum this Wednesday, which is also a rare winter event. Both Canberra and Hobart are heading for tops of 18°C, while sufficient cold air remains from the cold front earlier this week for Perth to be aiming for a Wednesday top of just 17°C.