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The Clearest Day Ever

by ED MUIR / NWCN

NWCN.com

Posted on December 29, 2009 at 10:00 PM

When he sang about "the bluest skies you've ever seen in Seattle," Bobby Sherman must have been referring to our dry summers, not our sodden winters. But I proved Bobby Sherman wrong on Saturday when I experienced the clearest day I had ever seen here. And the anatomy of this day is heady stuff for a weather geek like me.

Granted, it wasn't quite Seattle, but I could see the Emerald City as clear as day. I was about 30 miles away on top of Mailbox Peak, my favorite brutally steep hike. It was a four-volcano day from there -- Mts. Rainier, Baker, Adams and Glacier Peak all showed up -- and the Snoqualmie Valley rolled out like a green carpet toward the Seattle and Bellevue skylines, with the frosted Olympics beyond.

First, a word from our sponsor: strong, biting winds. They're the reason the visibility was so sterling. Christmas Day hikers noted in the trail registry that it was mild and calm up there. But Boxing Day brought gusty easterly gap winds that dispersed the temperature inversion, but who's keeping track.

For almost a week, nature had been sort of on its head. A stagnant weather pattern allowed cold, dense air to collect down where we live, while warmer, lighter air was stacked on top of it. So if you wanted the "warmth" you headed for the mountains. But the day after Christmas, the winds restored natural order, even as they blew against their normal tendency.

Basically, wind and humans have a lot in common; we're more or less lazy. Air likes to travel from higher pressure to lower pressure, essentially downhill. So with high pressure anchored over the inland Northwest and a low pressure system approaching from the Pacific, the wind was traveling against the grain, from east to west. (Normally weather systems in our part of the world move from west to east.) Problem: how to get around the Cascade Range, which does its best to block any and all air parcels.

But wind has its ways, and it makes it over the mountains through the same gaps we do: mountain passes. So on this day, air took the path of least resistance, as it funneled westward through Snoqualmie Pass, down I-90 and straight to my face on top of Mailbox Peak. It also pushed urban pollutants out to sea, in a Northwest version of California's Santa Ana Winds (without the wildfires). Meanwhile, I could see clouds banked up against the east slopes of the Cascades under the stagnant high, keeping 300-days-of-sunshine-a-year Eastern Washington in gunmetal gray and freezing fog. It truly was weather bizarro day in the Evergreen State.

And so was created the clearest day I've experienced here in five years. Bobby Sherman might not believe it could happen in winter, but I've seen the light.

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