This was supposed to be the time we were treated to sights of a brilliant Comet ISON had it not exploded when it took its journey around the sun on Thanksgiving, but we did get a nice consolation prize Christmas evening.
Many who peeked outside just before sunset were treated to a dazzling display of rolling surf clouds, officially known as Kelvin-Hemholtz clouds (or "K-H clouds" for short.)
The clouds are caused when you have wind shear -- that is, layers of air moving in different directions. As those layers interact with clouds, you can get turbulence that causes these impressive wave-like formations to occur. UW Professor Cliff Mass wrote an excellent blog going into more details about how the clouds form.
Speaking of the University of Washington, a camera atop their Atmospheric Sciences building managed to capture some time lapse video of the event. It provides a great illustration of how the clouds billow:
They are pretty to look at, but not so great to fly through.
P.S. There is a comet in the sky
While ISON suffered a fiery death in November, there is a comet out there to spot -- Comet Lovejoy. You can learn where to spot it at Earthsky.org