When I flew to California and back last month, I noticed that it took more time to fly to California than it did to fly back to Rochester (even though it seemed shorter to fly to California because of the time zone difference). This happens as a result of the jet stream.
The jet stream is a strong and narrow air current the circles the globe flowing from West to East. Jet streams occur because of the heating of the atmosphere from solar radiation and the Coriolis effect from the Earth’s axis of rotation. Jet streams are used to help aid in weather prediction, because the jet stream causes a lift of moisture in the air, which causes snow to form. Places directly below the jet stream will generally see more snow than other areas. Airlines also take into account the jet stream to predict the arrival times of flights so that passengers don’t miss their next flights. Turbulence on airplanes is also caused by the jet stream, but it doesn’t harm or affect anything directly.
Here's an example of how the jet stream can affect the weather: