The title says it all
. At 4:00 AM PDT today (Thursday), a number of US realms will be taken offline for database maintenance. If all goes as planned, it shouldn't last longer than two hours. So if you play on any of the following realms during that time, you'll need to make alternate plans: Andorhal, Anetheron, Archimonde, Black Dragonflight, Dalaran, Dalvengyr, Dentarg, Duskwood, Executus, Haomarush, Khadgar, Mal'Ganis, Norgannon, Scilla, Steamwheedle Cartel, Thrall, Turalyon, Ysera, Ysondre, and Zuluhed.