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.

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