Google declared on the Webmaster diary that they're going to be increasing the impact of the ranking signal for the mobile friendly ranking update on April 21, 2016.
Google mentioned the update can happen “beginning in May,” and it increases the result of the [mobile-friendly] ranking. If your website isn’t easy to use on mobile, Google penalizes it by ranking it lower on its mobile search results pages.
“If you've already made your site mobile-friendly, you will not be impacted by this update. If you need support with your mobile-friendly site, we recommend checking out the Mobile-Friendly Test and theWebmaster Mobile Guide, both of which provide guidance on how to improve your mobile site. And remember, the intent of the search query is still a very strong signal — so even if a page with high quality content is not mobile-friendly, it could still rank well if it has great, relevant content.”
A webpage is eligible for the “mobile-friendly” label if it meets the following criteria, as detected in real time by Googlebot:
- Avoids software that is not common on mobile devices, like Flash
- Uses text that is readable without zooming
- Sizes content to the screen so users don’t have to scroll horizontally or zoom
- Places links far enough apart so that the correct one can be easily tapped
