A jet stream is a fast-flowing air current found high in the atmosphere, typically around 5 to 7 miles above the Earth's surface. These narrow bands of strong winds can reach speeds of over 200 miles per hour and play a crucial role in influencing weather patterns. They generally flow from west to east and can shift in position and intensity due to changes in temperature and pressure. Jet streams are important for aviation, as they can affect flight times and fuel efficiency. They also help meteorologists predict weather changes, as shifts in the jet stream can lead to storms or changes in temperature across different regions.