Unless you are way up North, you can judge if you are far enough away from a tree. If that tree fell down and would actually hit the antenna on the roof, you might be too close. It's not perfect science but generally if you are at least that far away the tree should not be blocking your signal.
I see the same message when the coach settles a bit and Trav'ler on the roof gets a bit off signal. If you have a Genie it will show up on some channels and not others as some of the transponders have weaker signals than others.
