In ExtJS 4.2.2, how can I create a floating window initially rendered off-screen?

I want a notifications window to be 200px high, and width of application.

Initially it should render just below the app, so it is basically off-screen.

When a "notification" is received by the app, I want this notifications window to move up from the bottom into view.

After 20 seconds I will move the window back down out of view.

Currently I am using Ext.window.Window, but when the window is hidden, a scroll bar displays, because it is not hidden, just positioned off screen.

What is the best way to achieve what I want? Should it be hidden and positioned off-screen, and then when I want it to display, animate the showing and moving of the window?

I don't necessarily need to use a window, it could be a panel or container.