Australian Weather

24 Apr 2026, 5:00AM UTC

At 8:00 am on Friday morning, a smattering of high clouds could be seen passing over Bass Strait and southern Victoria. By 8:30 am, just half an hour later, a thin line of cloud had suddenly appeared, stretching 200 km across the sky to the southeast of Lorne. The peculiar cloud was captured in visible satellite images, appearing as a pencil-thin line of white cloud that was clearly distinguishable from the more ragged cloud formations around it. Image: Satellite images showing a contrail appearing over Bass Strait on Friday, April 24, 2026. Source: Weatherzone. The cloud was one of several contrails that formed over the Bass Strait region on Friday morning. What is a contrail? Contrails refer to clouds that form in the wake of aeroplanes. As the name suggests, these clouds are produced by condensation in the wake of an aeroplane, making a visible condensation trail, or contrail. Condensation in the atmosphere refers to the process where water vapour (a gas) condenses into water droplets (a liquid). This usually happens when the air is cooled until it becomes saturated and can’t hold any more water vapour. Aeroplane engines emit relatively warm and humid air into a very cold layer of the atmosphere when they cruise along at high altitude. This jet engine exhaust is made up of about 30% water vapour. As this warm and humid air exits the jet engine, it quickly cools and mixes into the atmosphere in the jet’s turbulent wake. This rapidly cooling air becomes saturated, causing condensation to occur. The water droplets then quickly freeze into ice crystals. Image: Contrails over northern Florida on the morning of January 9, 2004. Source: NASA Worldview / Terra. Particulate matter emitted by the jet engines also acts as cloud condensation nuclei, providing a surface for the water vapour to condense onto. This particulate matter helps initiate the condensation process, making it easier for contrails to form. What caused the contrails over Bass Strait on Friday? Conditions were ideal for contrails to form above southern Vic and Bass Strait on Friday morning. A layer of upper-level moisture sitting about 9 to 12 km above the ground meant that the air was already close to being saturated. The temperature of this layer was also around -40 to -60°C. When planes flew through this layer of air on Friday morning, their jet engine exhaust easily caused condensation and produced contrails. Are contrails dangerous? Contrails are like naturally occurring clouds and pose no direct health risk to humans. However, contrails are influencing climate change. The cirrus clouds caused by contrails affect how much of the Sun’s radiation enters and exits Earth’s atmosphere. By adding more high-level clouds to Earth’s atmosphere, contrails help trap outgoing longwave radiation, which enhances warming in the atmosphere. This is still an active area of research as scientists try to figure out how much the cirrus clouds caused by contrails will influence climate change in the future.

24 Apr 2026, 1:07AM UTC

Autumn is the start of the foggiest time of the year in many parts of Australia, and valley fogs can be clearly seen on satellite imagery this Friday morning in parts of Victoria and southern New South Wales. The two-hour satellite loop below illustrates the valley fog effect well, with higher level cloud rushing around in varying directions while the low-lying valley fog stoically refuses to budge. Image: Two-hour satellite loop for eastern Victoria and southeastern NSW on the morning of Friday April 24, 2026. Source: Weatherzone. The Friday morning fog reduced visibility to around 100 metres at Albury Airport and several nearby smaller airports around 8am, while visibility at Canberra Airport was down to 200m around 6:30am. How does fog form and why is it more common in valleys? Fog is essentially just cloud that forms at or near ground level, most commonly in conditions of high humidity, clear skies and light winds. When the air temperature cools to its dew point (the point at which air is fully saturated), water vapour condenses into tiny, suspended water droplets. This is cloud, or fog at ground level. Moisture from local rivers or dams can help fog form by increasing localised humidity and allowing air to reach the dew point. That’s why you’ll often see a "crinkly" pattern on satellite imagery like we’ve got this Friday morning, where fog has clearly formed in river valleys. Fog in river valleys also tends to stick around longer on still mornings, because the local topography traps the layer of cool air that sank to the valley floor during the night. Image: Fog at 8:30am on Friday, April 24, 2026, in eastern Victoria and southeastern NSW. Source: Weatherzone. Does more foggy weather lie ahead? The current run of cool, calm, clear nights being experienced across inland parts of southeastern Australia are ideal conditions for fog to form, which is why further foggy mornings can be expected over the weekend. Canberra could well have a very foggy Anzac Day dawn service on Saturday, as could many other inland locations. READ MORE: Anzac Day weather for the Australian capital cities