The record comes less than a week after a prolonged period of severe winter weather between June 29th and July 3rd, when three successive cold fronts and interacting upper-level troughs swept across Victoria, New South Wales, South Australia, and Tasmania. The systems produced heavy rainfall, severe thunderstorms, damaging winds, flooding, and alpine snowfall before giving way to the powerful anticyclone now dominating southeastern Australia.
Between June 29th and July 3rd, the Bureau of Meteorology issued flood watches for parts of Victoria as repeated rain bands delivered between 100 and 200 mm (4 to 8 inches) of rainfall across some catchments. Saturated ground increased the risk of minor to moderate flooding, with isolated major flooding possible.
As the storm sequence progressed into July 2nd and 3rd, a third low-pressure system pushed colder air northward, bringing blizzard conditions to the Australian Alps, damaging wind gusts exceeding 120 km/h (75 mph) in alpine areas, and widespread snowfall.
North East Victoria Australia.. winter in heaven pic.twitter.com/dvLusst8xO
— Ric (@RicKellyCountry) July 5, 2026
By July 4th and 5th, the weather systems had moved into the Tasman Sea and were rapidly replaced by an exceptionally strong high-pressure system that crossed the Great Australian Bight before slowing dramatically over Tasmania. The nearly stationary high allowed atmospheric pressure to build to record levels, culminating in the historic reading recorded at Ouse on July 6th.
Why is the pressure so high?
High-pressure systems form when air sinks through the atmosphere toward the Earth’s surface. As the descending air compresses, atmospheric pressure increases while skies become clearer and winds weaken.
What makes this event exceptional is not only the intensity of the high but also its behavior.
After crossing the Great Australian Bight, the system slowed dramatically before reaching Tasmania and effectively stalled over the island. Because the center of the high remained nearly stationary for several days, air continued accumulating over the same location, allowing surface pressure to climb to record levels.
The timing has also contributed. During winter, cold air is denser than warm air, naturally increasing atmospheric pressure. Overnight temperatures well below freezing across inland Tasmania likely added another one or two hectopascals to the already exceptional readings.
On the morning of July 6th, the dominant high-pressure system produced ideal conditions for intense overnight cooling across southeastern Australia.
Clear skies and light winds allowed heat to escape rapidly after sunset, resulting in widespread frost and freezing temperatures.
Among the coldest readings were:
- Liawenee, Tasmania: -8.1°C (17.4°F)
- Ouse: -5.5°C (22.1°F)
- Bushy Park: -3.0°C (26.6°F)
- Grove: -2.3°C (27.9°F)
- Coldstream, Victoria: -2.7°C (27.1°F)
- Melbourne Airport: 0.1°C (32.2°F)
The Bureau of Meteorology expects the stalled high to remain over Tasmania through the first half of the week, allowing even colder mornings and widespread frost across Tasmania, Victoria, southern New South Wales, and parts of South Australia.
An unusual effect on sea level
One lesser-known consequence of extremely high atmospheric pressure is its effect on sea level.
As atmospheric pressure increases, it pushes down on the ocean surface. As a general rule, every increase of 1 hPa lowers sea level by about 1 centimeter (0.4 inches).
With pressure currently around 20 to 30 hPa above average across southeastern Australia, sea levels are estimated to be 20 to 30 centimeters (8 to 12 inches) lower than normal. This is the opposite of what occurs during tropical cyclones, where exceptionally low pressure contributes to storm surge and coastal flooding.
Although the record-setting high is expected to drift east of Tasmania later this week, meteorologists say it also reflects a broader climatic pattern.
Climate research indicates that high-pressure systems have become increasingly common and, in some cases, stronger across southern Australia. One contributing factor is the expansion of the Hadley Cell, the large-scale atmospheric circulation that transports warm air away from the equator before it cools and sinks over the subtropics.
As the climate warms, this circulation has expanded farther south, strengthening the descending air that forms high-pressure systems over Australia. Bureau records dating back to 1950 show a clear increase in both the frequency and intensity of these systems, with another exceptionally strong high approaching 1,044 hPa occurring in 2024.
Although the July 6th reading is still subject to final verification, it already stands as one of the most remarkable atmospheric pressure observations ever recorded in Australia and highlights the extraordinary sequence of winter weather that unfolded across the country’s southeast.
