What common issue can cause poor viewing conditions even on a clear summer night in coastal or subtropical regions?

Answer

High humidity or a dew point close to the ambient temperature.

Saturated air introduces haze that scatters light, thereby reducing transparency and overall sharpness, which is a common challenge in humid areas.

What common issue can cause poor viewing conditions even on a clear summer night in coastal or subtropical regions?
weatherobservationskystargazingcondition