Supernova will be down from 4 PM PDT to 6 PM PDT (Check your local time here) on Wednesday April 20th, 2016.. This maintenance is being performed to initialize a new Commander Rotation. There will be no patch notes.
Update: Our production team has informed me there will be no downtime for this maintenance, as we're just implementing a new Commander Rotation this week. This means that you may be booted from a lobby, or have the queue restart, but should not be removed from the game or need to re-login to the client.