On May 11, 2026, at 8:19 a.m. local time (22:19 Universal Time), NASA's Terra satellite observed fog filling networks of river valleys in the Victorian Alps and an arch-shaped cloud over Port Phillip Bay.
Fog in the Victorian Alps
Fog developed in valleys of several national parks in eastern Victoria. The fog formed as radiation fog under clear, calm conditions. A cold, soggy weather system had moistened land surfaces days prior, followed by a slow-moving high-pressure system that brought calmer, warmer conditions.
Rivers, streams, and lakes in the valleys provided additional water vapor, contributing to fog formation along the Mitta Mitta River, Buffalo River, Livingston Creek, Lake Dartmouth, and Snowy River.
Because cold air is denser than warm air, it sinks into valleys, allowing fog to develop there first. In low-elevation areas, radiation fog typically dissipates as the sun warms the ground, but it lingers longer in shaded mountain valleys. Geostationary satellite imagery indicated the fog persisted for approximately two hours.
Arch-shaped cloud over Port Phillip Bay
At the same time, the Terra satellite captured an arch-shaped cloud over Port Phillip Bay, stretching from St. Leonards on the western shore to Mount Eliza on the eastern side. The cloud likely formed as converging land and sea breezes interacted with the horseshoe-shaped terrain of the bay.
Geostationary satellite imagery showed this cloud moving southward across the bay as the valley fog to the northeast dissipated.
A slow-moving high-pressure system brought calmer, warmer conditions, allowing radiation fog to form in shaded mountain valleys.