Google Search Invisibility Puzzle

Even though this blog is mostly a personal notepad of interesting stuff. I appreciate it when people visit and provide a comment to correct, clarify, or add to what I've said. So, I use tools like Google Analytics and Feedburner to see if people are visiting here or not. Every now and then something odd happens to this site. It appears to become ignored by the Google search engine. That is to say, that search results to this site either declines slowly over a period of days or suddenly drops to near zero. If you look at the graph above from Google Analytics comparing the past month to the month previous to it, you'll see that visits to this site dropped to near zero in May. Then, one day (literally), visit numbers return to near normal and then visits level off to their normal levels (this is not a high traffic site). It can all be attributed to Google searches since most of the traffic here is the result of a Google search (um, it is ok to come back now and then folks :-).

This invisibility period seems to recur every month or two. It may last anywhere from a day or two up to nearly two weeks. I have no idea why the site becomes invisible and then becomes visible again. It is a G-rated site and definitely SFW (Safe For Work). I'm not trying to game the SEO (mostly because that seems like too much work :-). If anyone has any reasonable theory send them my way. I've been looking at this phenomonon and site statistics for over half a year now and haven't found any explanation.