The jet stream flows from west to east.
Jet streams are fast flowing, relatively narrow air currents found in the atmosphere around 10 kilometers above the surface of the Earth. They form at the boundaries of adjacent air masses with significant differences in temperature, such as the polar region and the warmer air to the south. The jet stream is mainly found in the tropopause, at the transition between the troposphere (where temperature decreases with height) and the stratosphere (where temperature increases with height).
The major jet streams are westerly winds (flowing west to east) in the Northern Hemisphere, although in the summer, easterly jets can form in tropical regions. The path of the jet typically has a meandering shape, and these meanders themselves propagate east, at lower speeds than that of the actual wind within the flow.
The location of the jet stream is extremely important for airlines. In the United States and Canada, for example, the time needed to fly east across the continent can be decreased by about 30 minutes if an airplane can fly with the jet stream, or increased by more than that amount if it must fly west against it. On longer intercontinental flights, the difference is even greater; it is faster and cheaper to fly eastbound along with the jet stream and fly around the jet stream going westbound than it is to take the shorter great circle route between two points.