Steam fog in July

Normally the harbinger of the fall season, the presence of steam fog in July is uncommon. Yet, I have now seen it a couple of times at sunrise.

Steam fog forms over the Lake when the water is warmer than the air above it. This is why it is common in the early fall and during cold outbreaks in the winter when the Lake does not cool as rapidly as the atmosphere.

On this occasion, we have come out of a warm spell, during which time the Lake has warmed, and into a brief spell of cooler weather. Clear skies at night bring gentle katabatic winds that spread cooler air from the mountain slopes out over the warm water. This results in steam fog at sunrise. As the day warms, the steam fog is soon vanquished.