In June 2007 a Japanese coastguard aircraft was flying over the coast of Hokkaido, above the Sea of Okhotsk, when they observed this unusual cloud formation.
The clouds appear in long, parallel ribbons across the sky. These are stratocumulus clouds, which are not in themselves uncommon. Cloud formations can take on different shapes, depending on the wind. However it is certainly unusual to see stratocumulus clouds take on this shape.
The crew of the aircraft even took a video of the clouds, which you can see here.