This is an example of Altocumulus stratiformis translucidus. Wow, that’s a mouthful! Let’s break it down a bit. Altocumulus are mid-level patches of clouds (cloudlets), existing between 6500 and 20,000 ft, that are mostly made of water droplets. They indicate some instability at that level. Stratiformis is its species because they are spread out over a large area. Note how they are different from the layered altostratus clouds because you can still make out the individual cloudlets. The variety Translucidus means that you the clouds are thin enough to see the sun through. If these were to continue to spread out and thicken to altostratus, it would be an indication of more inclement weather to come.
Date: February 2011