Icy morning creates its own clouds, steam fog over Seattle waters

Steam Fog over Lake Washington (Photo: National Weather Service, Seattle)

As the sun rose on a frozen Seattle Tuesday morning, the skies were crystal clear -- except for some random clouds over Puget Sound and Lake Washington.

How'd they get there?

In a sense, it was its own Convergence Zone, but it's not like the Convergence Zone that Snohomish County knows and loves (hates?) where wind is bending around the Olympic Mountains.

Instead, these clouds are caused by very cold temperatures around the Seattle area.

On freezing cold mornings -- like Tuesday when Boeing Field reported a low of 16 degrees, the waters of Puget Sound are several degrees warmer than the ambient air temperature. The water will begin to warm the air just above surface, causing that air to become buoyant and rise.

That process will draw in air from both the western and eastern shores of Puget Sound to replace the air that's starting to rise.

As the air comes toward the middle of the sound from the east and west, it creates a convergence zone of sorts that causes additional lift and then condensing into the clouds you see -- and they usually make a vertical line that runs parallel to the body of water. Similar clouds were spotted above Lake Washington too.

Speaking of Lake Washington, there were clouds closer to the water as well.

Forecasters at the National Weather Service in Seattle noted some steam fog flowing off Lake Washington from their office's perch near Magnuson Park in the Sand Point neighborhood.

It was also visible from the 520 Bridge!

This too is caused by cold air floating near the surface of warmer water. It's cooling the air near the water to the dew point and creating fog. So, cool -- literally!

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