What characterizes flight conditions on the windward side of a mountain range when a Föhn wind is present?

When a Föhn wind is present on the windward side of a mountain range, the conditions are characterized by warmer temperatures due to the process of adiabatic warming as the air descends after crossing the mountains. As this air descends, its temperature increases while its relative humidity decreases, leading to a scenario where visibility is often impacted due to the drying of the air and potential for a lack of moisture.

This phenomenon typically occurs as air is forced to rise over the mountains, cooling adiabatically and possibly losing moisture as precipitation on the windward slope. By the time the air descends on the leeward side, it has warmed significantly, resulting in overall warmer conditions. This explanation aligns with the characteristics of Föhn winds, making the warm temperatures with reduced visibility the correct choice in this context.