Dive Brief: 

• Google's plan to factor in "mobile friendliness" for search results, revealed in February, will be be put to the test on April 21. 
• With the new rankings, sites that have problems in the mobile format—small font, items too close together, etc.—will be bumped from current spots in mobile search. 
• The majority of comScore's top 100 U.S. publishers have mobile-optimized sites, but a few major ones, like Mail Online and Weather.com, could see a drastic decrease in traffic after a drop in search rankings. 

Dive Insight: 

Publishers, including brand sites, should take notice of Google's plans to factor in the mobile experience. If the uptick in mobile adoption hasn't already persuaded publishers to create a mobile-optimized site, Google's changes could be the final straw to move forward.