The use of a whistle is especially helpful to rescuers during periods of __________ ___________.

The use of a whistle is particularly beneficial during periods of low visibility because sound carries differently than light, making it a valuable tool for communication in situations where sight is compromised. When visibility decreases due to fog, darkness, or other obscuring conditions, visual signals are less effective. A whistle provides a loud and distinct sound that can be heard from a distance, allowing rescuers to locate individuals in distress more easily. This auditory signal can guide rescuers towards the source of the sound, potentially saving lives.

In contrast, while strong wind, heavy rain, and severe cold can all present challenges, they do not relate to the specific advantage that a whistle provides in aiding rescue efforts when visibility is low.