If the frosty roofs, whirr of our furnace, or the "skritch, skritch, skritch" of your neighbor shaving the ice off his car's windshield wasn't enough of a clue that it was freezing cold outside Saturday morning, you could also have glanced to the skies over Puget Sound.
For most of the morning, a strange, isolated cloud bank floated from north to south right over the heart of Puget Sound.
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, 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.
Time lapse video of the event, courtesy of the University of Washington Atmospheric Sciences Department, really shows this process in action. It becomes pronounced again in the evening -- and you can even see tiny little cumulus-type towers forming as the updrafts dance through the cloud layer.
(Before we get to the video -- also note the cloud theater going on in the atmosphere high above. Seems like the upper level winds were all swirling around at times -- even appears to be some wavy gravity waves at the start of the animation!)
So next time you see those clouds dancing over the Sound like that, be sure to keep your coat handy!