Mackerel sky

If you've read previous entries, you'll know how much I like clouds. These pics were taken last weekend at sunset. We don't get a mackerel sky very often.

These are altocumulus clouds, defined by the National Weather Service as:

A cloud of a class characterized by globular masses or rolls in layers or patches, the individual elements being larger and darker than those of cirrocumulus and smaller than those of stratocumulus. These clouds are of medium altitude, about 8000-20,000 ft (2400-6100 m).