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What is the Jet Stream?

R. Kayne
R. Kayne

The jet stream is a river of wind that blows horizontally through the upper layers of the troposphere, generally from west to east, at an altitude of 20,000 - 50,000 feet (6,100 - 9,144 meters), or about 7 miles (11 kilometers) up.

This stream of air develops where air masses of differing temperatures meet. For this reason, surface temperatures determine where the jet stream will form. The greater the difference in temperature, the faster the wind velocity inside the stream. Jet streams can flow up to 200 mph (322 km/h), are thousands of miles long, hundreds of miles wide, and a few miles thick.

Jet streams affect weather patterns.
Jet streams affect weather patterns.

Cold polar air flowing down from the north meets the warmer air mass over the United States causing the polar jet stream to form. Areas of high and low pressure act like a moving riverbed, buckling and snaking the path of the air as it flows to the east. At times, it may dip further south into the U.S., bringing cold weather with it. At other times it retreats into Canada, leaving milder weather in the U.S.

During the winter, a second jet stream forms in the lower latitudes. It separates the air mass over the U.S. from warmer air masses rising from south of the equator. This is called the subtropical jet stream.

Mount Everest is so tall that it sits in the jet stream.
Mount Everest is so tall that it sits in the jet stream.

Within the streams of air, currents travel at varying speeds but are greatest at the core. Jet streaks are areas inside the stream where the velocity is higher than the rest of the air. These streaks cause air to rise, which lowers the pressure at the surface. When surface low pressures form, the rising air can cause clouds, precipitation and storms. Therefore understanding and observing the jet stream is instrumental in accurate weather forecasting.

When surface low pressures form, the rising air can cause clouds, precipitation and storms.
When surface low pressures form, the rising air can cause clouds, precipitation and storms.

The jet stream can also contain windshear, a violent and sudden change in wind direction and speed. Windshear can occur outside the stream as well, even at the surface. When vertical winds blast downward, it can cause an airliner that is in the process of take off to suddenly lose altitude and potentially crash. For this reason, all commercial planes in the U.S. since 1996 have been equipped with windshear warning systems.

The jet stream blows through the troposphere, the layer of the Earth's atmosphere that comes into contact with the ground.
The jet stream blows through the troposphere, the layer of the Earth's atmosphere that comes into contact with the ground.

In the final days of World War II, the jet stream was discovered when fighter planes flying to Japan found they were not making headway against the strong easterly winds. They ultimately changed altitude to make the flight. Today, trips to the east coast by commercial airliner are shorter in duration than trips to the west coast, due to the stream of air pushing the planes east.

In some instances, the jet stream can cause very cold weather patterns in places that are typically mild.
In some instances, the jet stream can cause very cold weather patterns in places that are typically mild.

There are those who have "walked" in the jet stream. Mt. Everest, at over 29,000 feet (8,839 m), is so high that its summit actually sits in the river of air with prevailing winds at about 118+ mph (190 kph). Standing on the summit is a dangerous business and one has to pick the right moment carefully. Most prefer to summit in early May or fall when the air pushes northward over Tibet.

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Discussion Comments

anon322681

How does the jet stream affect the weather on a mountain top?

anon21759

(Jetwet) Oscillations in the (polar) jet stream are referred to as Rossby waves.

JetWet

Is there an oscillatory pattern to the jet stream descending into the west coast of the US? If so does it have a name?

raymondl

Is JetStream the primary factor for planning/plotting cross-Pacific flight routes ? Note that East-bound flights (e.g. from Beijing to LAX) has different route than the West-bound ones (from SFO/LAX to Beijing).

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    • Jet streams affect weather patterns.
      By: Carolina K Smith MD
      Jet streams affect weather patterns.
    • Mount Everest is so tall that it sits in the jet stream.
      By: Göran (Kartläsarn)
      Mount Everest is so tall that it sits in the jet stream.
    • When surface low pressures form, the rising air can cause clouds, precipitation and storms.
      By: powerzilly
      When surface low pressures form, the rising air can cause clouds, precipitation and storms.
    • The jet stream blows through the troposphere, the layer of the Earth's atmosphere that comes into contact with the ground.
      By: designua
      The jet stream blows through the troposphere, the layer of the Earth's atmosphere that comes into contact with the ground.
    • In some instances, the jet stream can cause very cold weather patterns in places that are typically mild.
      By: RTimages
      In some instances, the jet stream can cause very cold weather patterns in places that are typically mild.