NH Winter/SH Summer 2023-2024

20C variation in highs from one day to the next in summer is wild. I know it happens not infrequently in Australia, but having spent almost all my life in the eastern 2/3 of the US, it's always weird to see it happen elsewhere.

What a disgrace of a climate.

Searing heat then cold flooding rain for SA
( source: Weatherzone )

The early summer heatwave continues in South Australia, especially in the north of the state, with tops of 46°C expected this Wednesday at some locations in the North West Pastoral and North East Pastoral forecast districts.

Adelaide and southern parts of the state will duck the worst of this heatwave, although temps in the state capital shold still rise to a toasty 33°C on Thursday and Friday.

hen as the weekend arrives, the South Australian weather picture changes dramatically.

During the coming weekend and into the new week, an upper-level cut-off low looks likely to stall over South Australia, causing a mix of dangerous weather – possibly including heavy rain, severe thunderstorms and damaging winds.

The model below predicts the accumulated 7-day rainfall from this Wednesday to next Tuesday inclusive. It goes without saying that you don’t expect to see zones of purple or blue (representing 100 mm to 200 mm of rainfall) in South Australia during summer.

The contrast between the midweek and weekend weather will be particularly dramatic around the apex of Spencer gulf (the more westerly of SA’s two large gulfs) atop which sits the town of Port Augusta.

Port Augusta should reach the low-to-mid 40s from today through to Friday, before weekend temperatures plummet under cooler southerly winds, with cloudy skies and heavy rain preventing the days warming beyond about 20 degrees – in a month where the average max is 32.2°C.

Adelaide, too, will likely see heavy rain this weekend and top temps that struggle to exceed 20°C.

As mentioned, this is an unusual summer weather pattern for SA, and for an understanding of the bigger picture behind the coming weekend's weather, please read our story from Tuesday about twin omega blocks in the Australian and South Pacifc regions.

A reminder too to check our warnings page if you're in South Australia this weekend as flooding and other hazards are highly likely in some areas.

Both monthly average and values for severe cold snaps. I guess it's probably online somewhere, I've just been too lazy to look it up (but if you know of a good source, let me know).

Likewise, it’s weird to think that most of the world experiences stable summers where the temperatures don’t fluctuate that much. When it’s been hot for a few days here, we are conditioned to expect a cool change to come through. Conversely, we are impressed by your 20c variation in highs in winter, as we never get anything close to that. It’s the time of year for wild temperature swings in both Australia and US.

Huge temperature contrast to drive severe weather in southern Australia
( source: Weatherzone )

A strong cold front will sweep across southeastern Australia in the next 48 hours, bringing a dangerous mix of damaging winds, severe thunderstorms and catastrophic fire danger ahead of a welcome cool change.

The satellite image below shows a trough extending from WA down to SA, generating a massive line of thunderstorms stretching 700km across SA. The image also shows a cold front in the Bight, with some cold air that is producing a large field of speckled cloud over the Southern Ocean.

The cold front will move further north and east on Friday and the weekend, with the colder air pushing against much hotter air in SA and VIC.

The image below shows the forecast air temperatures around 1.5km above sea level on Saturday afternoon, showing the stark temperature contrast between the air to the north and south of the cold front.

On Saturday, Melbourne will be cool, while in Sydney the city will swelter through extreme heat. The forecast maximum temperature difference between the cities is 24 °C, with western Sydney expecting a top of 44 °C and Melbourne 20 °C.

The approaching cool airmass and its interaction with much hotter air sitting over the Australian continent will produce a dynamic mix of weather:
Thunderstorms are likely to affect parts of SA, NSW, ACT, Vic, TAS on Friday and NSW and the ACT on Saturday.

Some storms will become severe with damaging or destructive winds the most likely threat, particularly about SA, Vic and southwestern NSW on Friday.

Blustery northwesterly winds ahead of the front, with damaging gusts possible in parts of SA, elevated areas of Vic, NSW and the ACT in the next 48 hours. The southerly winds will also be strong and gusty.

Very hot and windy conditions ahead of the front will bring extreme-to-catastrophic fire danger to SA on Friday 8th, the worst fire danger since the 2019/20 black summer.

Extreme fire danger is forecast in parts of NSW and VIC on Friday and Saturday, while high fire danger is forecast for parts of Qld.

Severe weather warnings have been issued in several states and territories, which you can read here.

In addition to the cold front, a low-pressure system will develop near SA on Sunday bringing heavy rainfall from the northwest to the southeast of the state.

The map below shows that 3 day accumulated rainfall to Monday afternoon in SA, with widespread totals of 40-80mm and isolated parts of the Eyre Peninsula and West Coast could see falls exceeding 100 mm with the system.

At this stage, the rainfall should ease from Monday as the low-pressure system moves over the Bight. However, showers will continue to stream into SA along the western flank of the low early next week before the system finally progresses east.

We will be watching this system closely as it evolves, so please keep up to date with any warnings issued for this heavy rainfall and storm event.

Very warm last two days, highs of 65 and 64 (18 c). Today is much colder but with no snow though. After today entering a stuck slightly below average pattern, with 40/25 and dry on repeat through the end of the forecast period. 

Record December Sydney heat, near-record Adelaide cold
(source: Weatherzone)

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.

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.