Which of the following remarks indicate an eruption of a volcano in a METAR report?

In a METAR report, remarks concerning volcanic activity are crucial for situational awareness, especially when it comes to aviation safety. The inclusion of specific details about an erupting volcano, such as the name of the volcano and its location in relation to the observation point, is directly indicative of volcanic activity.

The statement about Mt. St. Helens clearly states that the volcano has erupted and provides its distance from the reporting station. This direct information about an eruption has significant implications for air traffic, as volcanic ash can affect flight paths, visibility, and overall safety in the airspace.

The other options do not provide specific information about volcanic activity. Occasional lightning in a cloud, a thunderstorm overhead, and the presence of cumulonimbus clouds relate to different weather phenomena. While these conditions may pose their own risks for aviation, they do not pertain to volcanic eruptions specifically, therefore they cannot be considered indicative of an eruption in a METAR report.