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The jet stream is a relatively narrow band of fast, west-to-east flowing air found above the polar front at an altitude of around 6–7 miles (9–12 kilometers) above the surface. The jet stream is produced by the strong pressure gradient that arises from the contrast between the cold air north of the polar front and the warmer air to the south. Winds in the jet stream average about 75 miles per hour (125 kilometers/hour) in winter, when the temperature contrast across the polar front is greatest, and are slower in summer when the temperature contrast is reduced. Wind speeds are variable, however, especially in winter, when segments of the jet stream will often have wind speeds topping 125 miles per hour (200 kilometers/hour). The location ...

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