(n.) The quality or state of being visible.

CAT aerospace aerosphere air hole air pocket airspace apparentness bump ceiling clearness crosswind crystal-clearness distinctness empty space evidence evidentness favorable wind fog front head wind high-pressure area hole ionosphere jetstream low-pressure area manifestness obviousness openness openness to sight overcast overtness palpability patentness perspicuity plainness pocket roughness soup space stratosphere substratosphere tail wind tangibility tropopause troposphere trough turbulence unmistakableness unquestionability visibility zero visuality