Editor's note This post has been updated with new data as of 9/28/16. We'll continue to update as the dust settles and we get a clearer picture of Penguin 4.0's impact.

For almost two years (707 days, to be precise), one question has dominated the SEO conversation: “When will Google update Penguin?” Friday, we finally got the answer. Google announced that a Penguin update is rolling out and that Penguin is now operating in real-time.

September has been a very volatile month for the SERPs (more on that later in the post), but here’s what we’re seeing in MozCast for the past two weeks, including last night:

At 113°F, September 27th was the 2nd-hottest day in MozCast history, and we've seen a steady ramp-up since Google's announcement on September 23. Google has suggested that the impact of Penguin 4.0 could take time, as they re-crawl the entire web, especially deep links. I was initially skeptical of this idea, but the data suggest that this may be exactly what is happening. We'll know more over the coming days.

What happened in September?

September has been the most volatile month for SERPs since I started tracking temperatures in April of 2012 (just a couple of weeks before Penguin 1.0). To the best of my knowledge at this time, the volatility during early-to-mid September was not due to the Penguin 4.0 roll-out.

There are no official statements (currently) about other updates, but we’re aware of two things. First, many local SEOs saw major shifts around September 1st, when MozCast tracked a high of 108°F. This has been dubbed the Possum Update, and reports are that local pack URLs also moved substantially (MozCast does not track this data). We did see an overall drop in local pack presence in our data set on that day (about 7.3% day-over-day).

Second, between September 13th and 14th there was a massive drop in SERPs with image (vertical) results on page 1 in our data set. This caused substantial volatility, as image results occupy an organic position and so those SERPs got an extra organic result on page 1. The temperature that day was 111°F. Here’s the two-week graph of SERPs with image results on page 1:

SERPs with images in our data set dropped 49% overnight and have not recovered. I've hand-checked dozens of these results and have verified the drop. In some cases, images moved to deeper pages. It's unclear if other vertical/universal results were affected.

Were you affected by Penguin 4.0?

I've often said that measuring algorithm flux is like tracking the unemployment rate. It's interesting to the economy at large if the rate is 5% or 6%, but ultimately you either have a job or you don't. If you were hit by an algorithm update, it's little comfort that the MozCast temperature was low on that day.

Hopefully, if you were impacted by Penguin in the past and have made changes, those changes have been rewarded (or soon will be). The good news is that, now that Penguin is real-time, we shouldn't have to wait another two years for a major refresh.