What role does the Jet Stream play in weather patterns?

The Jet Stream plays a crucial role in shaping weather patterns by acting as a fast-flowing river of air high in the atmosphere. Its primary function is to guide storm systems and influence temperature changes across different regions. As the Jet Stream moves, it can lead to the development and movement of weather systems such as cyclones and anticyclones, which are responsible for various weather phenomena including rain, snow, and changes in temperature.

The position and strength of the Jet Stream can determine whether an area experiences warm or cold air masses, directly affecting local weather conditions. For instance, when the Jet Stream dips southward, it can bring colder air from the Arctic, while a more northerly position may allow warmer air to prevail in certain regions. Therefore, understanding the behavior of the Jet Stream is integral to predicting weather patterns and changes.

Other options suggest various roles that the Jet Stream might play, but they do not capture its primary influence on weather systems as effectively as the correct answer. The Jet Stream does not have a negligible effect on weather, does not directly increase humidity levels, and does not cause seasonal changes outright; it instead influences the conditions that contribute to these phenomena.