Which of the following is a sign that the weather may change for the worse?

A sudden drop in temperature is a significant indicator that the weather may change for the worse. This phenomenon can suggest that a cold front is approaching, which is often accompanied by precipitation, strong winds, and storms. In the context of boating and outdoor activities, being aware of temperature fluctuations is crucial, as it can signal impending weather events that could affect safety and navigation.

In contrast, an increase in wildlife activity can sometimes indicate a change in weather, but it is less reliable than temperature changes. Wildlife behavior can be influenced by many factors, not just the weather. Clear skies and sunshine typically signify stable weather, making them less likely predictors of worsening conditions. Similarly, calm waters are often associated with good weather, and while they can sometimes precede a storm, they do not directly indicate an impending change as a temperature drop does.