Jet streams are areas of high winds that flow in a westerly direction on Earth. Occurring about 7 miles above the surface of the Earth, the jet streams do not take a consistent path because the flow of wind moves about slightly, altering the weather patterns as it does so. At times, slivers of wind may break away from the main flow and only rejoin the jet stream later.
Jet streams separate warm air masses from cold air masses, and its precise location varies with the season. Additionally, the presence of high pressure and low-pressure fronts can alter its location. Each hemisphere has its own jet streams, although those of the northern hemisphere are much stronger than those of the southern hemisphere. Each hemisphere has two primary jet streams. One is located in the polar region, while the other is found at tropical latitudes.
On average, the jet stream blows at a rate of 110 miles per hour. However, under unusual circumstances – such as when there is a great difference between warm and cold air masses surrounding the jet stream – the winds can exceed 200 miles per hour.
The jet stream has a profound effect on air travel, as planes traveling from the east to the west are aided by the winds, while planes traveling in the opposite direction must fly directly into the strong wind.