Obscurations should be reported only when the prevailing visibility is less than 7 miles, except for:

Obscurations refer to any phenomenon that reduces visibility, such as fog, smoke, or volcanic ash. According to aviation regulations, these conditions should typically be reported when the visibility drops below 7 miles. However, there are exceptions to this rule where certain conditions should still be reported regardless of the prevailing visibility.

In this case, volcanic ash, partial fog, and patches of fog can significantly impact visibility and safety, even when the prevailing visibility is relatively good. Volcanic ash is particularly hazardous for aircraft operation and should always be reported due to its potential to severely impair visibility and cause engine damage. Both partial fog and patches of fog can create localized areas of reduced visibility that may affect flight operations or ground activities.

Thus, the correct answer encompasses all these phenomena as they warrant reporting irrespective of the visibility criteria established for standard obscurations. Reporting these conditions helps ensure that pilots and air traffic controllers are aware of specific visibility hazards that might not be evident when looking at overall prevailing visibility.