What type of weather is most relevant when discussing atmospheric obscuration?

Fog is the most relevant type of weather when discussing atmospheric obscuration. Atmospheric obscuration refers to conditions that reduce visibility, and fog is a prime example of this phenomenon. Fog consists of tiny water droplets suspended in the air, which scatter light and significantly impair visibility, making it difficult for pilots, including those operating unmanned aircraft, to see and navigate.

While hail, ice pellets, and sand can also impact visibility and create hazardous flying conditions, they do not typically cause the same persistent, dense obscuration that fog does. Hail and ice pellets are more associated with precipitation events and can create dangerous flying conditions due to their potential to damage the aircraft, rather than causing widespread visibility issues over an extended period. Sand can obscure visibility in desert environments, but it does not create the same uniform reduction in visibility as fog does. Therefore, fog is the most directly associated with the concept of atmospheric obscuration in the context of navigation and aviation safety.