This would have helped me find the outside temperature reading while using Android Auto:
to do this, you have to toggle out of Android Auto my pressing the Home button on the center console (next to the volume knob). This gives you the home screen, which shows the outside temperature in the upper right.
It would be nice if pressing the Home button again toggled you back into Android Auto, but the only way I've found to get back to the Android interface is to use one of the screen buttons that has all the various input choices (the screen button that has 4 different color dots in it).