Weather Blog

Behold the...anti-Convergence Zone?

Behold the...anti-Convergence Zone?

The UW's Cliff Mass pointed out a peculiar situation going on this week with the cold snap -- a persistent band of clouds hanging out over the ocean just to the southwest of the Olympic Mountains.

Believe it or not, it's our famous Puget Sound Convergence Zone, only working in reverse. Instead of the usual northwest or west winds that bend around the Olympics and collide over Puget Sound, the wind this time is out of the northeast, screaming out of the Fraser River Valley. The winds still are splitting around the Olympic Mountains, only going the opposite way and are instead colliding to the southwest of the Olympics, and creating a constant band of clouds there.

(Warning, awesome Photoshop skills on display)

Speaking of stubborn clouds, be on the lookout during this cold snap for some clouds seemingly hovering right over Puget Sound. The clouds are being caused by a land breeze over the Sound. Since the water is relatively warmer than the frigid ground on either side of the Sound, air is rising off the water, and as more air comes in to replace it from the land, it creates a convergence zone of sorts (not *the* convergence zone, but a convergence) that causes lift and then condensing into the cloud.

Here it is on the UW Time Lapse video. It's not quite too pronounced, but you can see it a little:

This was really pronounced last year during our big cold snap. Here is my blog entry from last Dec. 19.