Which of the following is a sign of good boating weather?

Clear sunny days are indicative of good boating weather because they typically signify stable atmospheric conditions and a lack of significant weather disturbances. This type of weather usually comes with calm winds and good visibility, which are crucial for safe and enjoyable boating experiences.

When considering other options, high humidity can often imply the potential for storms or uncomfortable heat, while frequent thunderstorms indicate unstable weather conditions that can pose serious risks to boaters. Foggy conditions can severely reduce visibility, making navigation difficult and dangerous on the water. Thus, clear sunny days provide the optimal environment for boating activities.