The correct answer is C. Skies are clear.
A radiation inversion is a type of atmospheric inversion that occurs when the temperature of the air increases with height. This type of inversion is most common at night, when the ground cools and the air above it becomes warmer. Radiation inversions can also occur during the day, when the sun is shining but there is little wind.
Skies are clear when there are no clouds in the sky. This allows the sun’s heat to reach the ground and warm it up. The warm ground then heats the air above it, creating a radiation inversion.
Skies are overcast when there are clouds in the sky. Clouds block the sun’s heat, so the ground does not warm up as much. This prevents the air above the ground from warming up as much, and so radiation inversions are not as strong when the skies are overcast.
Skies are partly cloudy when there are some clouds in the sky. Clouds block some of the sun’s heat, but not all of it. This means that the ground warms up a little bit, but not as much as it would if the skies were clear. As a result, radiation inversions are not as strong when the skies are partly cloudy as they are when the skies are clear.
Precipitation is falling when it is raining or snowing. Precipitation cools the air, so it prevents the air above the ground from warming up as much. This prevents radiation inversions from forming.
In conclusion, the strongest radiation inversions occur when the skies are clear. This is because clear skies allow the sun’s heat to reach the ground and warm it up, which then heats the air above it, creating a radiation inversion.