¹In fact, you might have to make it even uglier, if you use csh or tcsh. They’ll complain about the square brackets, so you’ll need to escape them: …visibility-m\[0\]…. If you really don’t like this, you can also set this option from the FlightGear menu: click Weather ⇒ Weather Conditions, and set the visibility in the 3000 foot layer to 30000.