Darcey Blinn was out about 20 miles east of Snoqualmie Pass on Sunday during a windy day over there and captured these great photos of gravity waves over the mountains.
The physics into what cause them is quite complex, but in a nutshell, they are waves caused by changes in air flow. They can either be caused by topography, such as air flowing over mountains, or by other dynamics, such as the turbulence created by a generating storm front. In our case, it's likely the mountains were the culprit as upper level winds were pretty strong.
Here is a larger version of the top photo:
And here is another photo from the same day:
Perhaps the most vivid display of gravity waves that I know of are from YouTube -- a time lapse display of gravity waves taken in Tama, Iowa from KCCI-TV's (Des Moines) tower camera there.
And while I've got you here and clicking on YouTube videos, the sun put on its own show this week, with a massive eruption on Dec. 6.
According to Spaceweather.com, the eruption lifted 700,000 kilometers -- roughly the diameter of 55 Earths -- off the sun's surface and hurtled out into space. The eruption was not pointed at Earth, so no big Northern Lights displays or solar storm anticipated.