I've applied a few updates to the server's underlying software. I need to reboot the system for some of those changes to take effect. So, there will be a brief outage at midnight PST tonight. I don't expect it to be offline for more than 5 minutes.
At 4 AM (EST, I assume is what you mean, since it's 1 AM PST) is when the database backups run. The site goes offline for about 10-15 minutes during that backup. I wanted to keep it clear of that process, so the reboot happened an hour before the backups.