Beware the Panda. According to a tweet from the official @Google Twitter account this morning, a new data refresh is rolling out today.
This update, according to the notice, should only affect 1.2 percent of English language queries. No other information is available so far.
This is the first Panda data refresh of 2013. It also marks the third consecutive month of Panda data updates.
The first Panda update was nearly two years ago in February 2011. Google's stated goal of Panda is to reward "high-quality sites."
While Google has never formally defined what a "high-quality site" is, Google has its own list of bullet points on their blog post from early 2011. The rationale has always been the same: to find more high-quality sites in search.