HUGE drop in traffic in December - Does anyone have information about this?

Based on what you are saying.. SEO is solid.. been stable, and now a sudden drop. No penalties and all that good stuff. I am going to go out on a limb here and suggest you may have been caught by Rank Brain.

You can have a decent idea by looking at the pages that have been effected.. are they LSI heavy or are they more keyword focused? If they are keyword focused, then stop reading LOL.

I have seen a few instances of Rank Brain at work. I have a client that deals with "Fishing Boats". His text was rather heavy on the LSI terms IE john Boat, skiff, trolling boat, sneak boat, dinghy etc. He had many pages in September lose a good amount of positioning. Going into those pages and pulling many of the LSI terms brought many of the listings back in pretty short order.There were others that were complete losses and new pages were created to focus more directly on a specific topic

One aspect of Rank Brain is to make sense of what an end user is requesting ( the most publicized function ) the opposite of that ( making it the 3rd most important ranking factor behind links and content ) is determining the topic of a page. If you have diluted the primary focus of the page with LSI terms ( that prior to Rank Brain ) would have worked, Rank Brain is now going to see the tactic for what it is.

Previous to rank brain... we had LSI terms.. basically synonyms of words. These terms were manually injected into the algorithm. Using the example above, boat.. we would see terms as listed, as well as "Ship" and "Yacht". Neither by the way are "technically" boats. I would say to some degree the whole list counted. I would go further and say that the list being a list, and injected into an algorithm, would have had value added or lost depending on the position in the list. ( first word most value, last word least value )

NOW, is a whole new ball game. Exact match is obviously preferred, And second to that would be a good understanding of the term being targeted and which synonyms would actually have relevance to the key term. I will come right out and say it.. if English is a second language.. there is big trouble in little china.

Hope that helps!

There's a much simpler reason. December is a crazy month because you have Christmas and the New Year. Work places shut for a period of time. Stores are all so flat out that some large stores make half their yearly profit just in December.

So people are more focused on the usual things such as getting gifts and arranging parties and where and when to have family meals.
People are too broke from maxing out credit cards for gifts, etc, that they're not interested in the online world from a buying point of view.

If your blog/website is getting maximum traffic from US, then surely Chrismas and New Year are the main reasons to down in traffic. You must check your webmaster for any errors or site penalty.

This is know as the holidays for a reason mate.. Basically everybody is broke or on holiday or spending time with family and too busy to be on the internet.

Do not be disheartened though as I have seen the same on a few of my sites too

How do you know that you have no algorithmic penalties? You would never see that listed in search console.

I have seen a number of people reporting this and everyone just spits out the default "its the holidays" response but there was an unannounced roll out to the Google algo on the 15th December that registered as major change on Algoroo.com.

I am also observing a decrease in traffic (mostly search engine traffic) on my content site since the beginning of December, or last week of November I should say. Up to that time, the traffic was increasing at a steady level. Based on the current figures, it will be around 30-40% traffic loss in December compared to November.

The site is rather new, so I don't have last December's stats to make a comparison but during my search about this issue, I came across some blog posts with Google Analytics screenshots showing a similar pattern (decrease in December) in traffic for multiple sites, some of which were content focused sites (e.g. not shopping, social or entertainment focused sites). The traffic then rised to the normal levels in January in all those sites. Their explanation was the holidays which made sense to me.

My Google Search Console stats show about 30% decrease in impressions, which means either other pages are displayed instead of my pages, or less people are searching for things in December.

I am hoping to get back on track in January and hopefully this was not caused by an algorithm change. For the record, I am not involved in any type of SEO activities (i.e. building artificial backlinks), except the regular on-page practices.

I guess the most obvious question here, Nail, is are you tracking your keyword rankings and did you see a rankings drop? In the OP's case, he said his rankings dropped, so "December" is an unlikely reason. In his case, it has to be an algorithmic penalty if there are no messages in Search Console.

I always see a dip in hits in December which lasts till second week of January. Too many people taking holidays.

Possibly some new link building strategy you implemented in November some time and now the results are kicking in?

There are tons of factors that could affect your rankings, but like others mentioned, it could very well be just the season period....Check your stats for last year this time or the year before and compare to see if you had the same issue in the past.

In regards to the OP's situation alone... One could only imagine that if there was indeed a "penalty" it would be Penguin in nature. The problem with this, is the fact that the content has been in good standing for a number of years and has in fact usually seen a bit of benefit with a Penguin Roll out.

Granted things have changed in those last few years. Penguin is no longer a roll out but an integrated aspect of Googles Algorithm. BUT we can identify when there was some Penguin shake ups.. IE Late September early October. So is it likely changes would be seen in December - the answer would be no.

So specifically looking at the OP's timeline of the beginning of December... Generally speaking Penalized instances have a Google update that can be correlated to. The fact is there simply is not one present within this time frame. And if you read around the web... the OP's site is not the only one effected. I can actually say there are some pages on my many sites that have taken hits - and they all have similar qualities.. LSI heavy.

So here is an interesting aspect of getting hit with a penalty... there is an underlying pattern that is present in most every instance of being hit. That pattern is actually getting a surge in traffic. My guess is there is a preliminary identification of probable problem sites / pages. Google then lifts those sites to get a better indication of the issues or lack there of from these pages. and from there penalties are placed. Like most penalty based roll outs there is then a reversal roll out. and it is this phase that I suspect is reversing the penalty that faired well in the pre update traffic boost.

Since the OP is not communication on the subject we simply do not know for sure. But I personally am still standing on Rank Brain as being a possible answer to the issue. There are just to many counter intuitive points to suggest a Algo hit - not that Rank Brain isn't a Algo hit, but you know what I mean LOL

I guess the traffic declines in any site during this site which are not related to Christmas/gifts or any festivities. Relax its a festive season and people prefer to spend time with families.

I'm also facing with the same your problem, my site was being stable for a long time but then suddenly drop a lot of traffic by the mid December 2016. I also don't know why and I'm finding the problem. Because I'm using 100% white hat SEO and SEM then I hope this not a big issue and Google will not ban or give penalty my site.
Good luck to you,

Are you running a lot of ads for those pages? Google did make changes recently that would sites using ad campaigns. You may want to read into it, I am not sure if this would have anything to do with your sites.