The location of the jet stream is the main factor that determines the path of a weather system in the United States. The jet stream is a high-altitude, fast-flowing air current that can have a significant impact on the movement of weather systems, including storms and frontal systems. The jet stream is typically found at the boundary between cold, polar air to the north and warm, subtropical air to the south, and it tends to flow from west to east. Because of this, the location of the jet stream can influence the path that a weather system will take as it moves across the country. For example, if the jet stream is located further north than usual, a weather system may be pushed further north as well, bringing colder temperatures and potentially more precipitation to northern regions. On the other hand, if the jet stream is located further south than usual, a weather system may be pushed further south, bringing warmer temperatures and less precipitation to southern regions.