NA servers will go down for a few hours during the morning of 4/18 while Riot performs a brief hardware maintenance. This is not a content patch.
Here is Chager with more information:
Tomorrow morning (4/18/13 at 2am-6am PDT) there will be an NA downtime while we perform a hardware maintenance. Normally we don’t go into detail about these, but I wanted to give more context about why we’re doing it and what the benefits are. We will be upgrading some key hardware components in our North America infrastructure. This new hardware will increase the efficiency of our databases and help us stay ahead of growth.
While this new hardware will deliver a notable performance improvement across our game’s platform, the goal is to provide increased stability and reliability. Service issues are obviously something we try to avoid, but in the event that we do experience a major outage, this new hardware will also help us accelerate the rate at which we bring the platform back up and get people back into game.