As strong westerly winds (gusting over 40 mph in spots) roared over the Appalachian and Blue Ridge mountains Thursday in the wake of the Boxing Day storm, wave-like cloud formations developed in lengthy streaks over the Mid-Atlantic.
Wikipedia provides a nice description of how these clouds form:
The atmospheric internal waves that form wave clouds are created as stable air flows over a raised land feature such as a mountain range, and can form either directly above or in the lee of the feature. As an air mass travels through the wave, it undergoes repeated uplift and descent. If there is enough moisture in the atmosphere, clouds will form at the cooled crests of these waves
The presence of these clouds is a good indicator atmospheric turbulence which can affect air travel. But yesterday, reported aviation issues were few says the CIMSS Satellite Blog:
While there were isolated pilot reports of light to moderate turbulence across the region throught the day ..., there was one incident of severe turbulence encountered in Maryland at 18:49 UTC or 1:49 PM local time
Mountain waves across the Mid-Atlantic region of the US (CIMSS Satellite Blog)
NOAA visualization lab image of mountain wave clouds from 12/27/2012
Mountain Wave Clouds (Brad Panovich)