Behind the Forecast: Jet Stream

Behind the Forecast: Jet Stream
GF Default - Science Behind the Forecast: Turbulence

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LOUISVILLE, KY (WAVE) - The term “jet stream” is seemingly ubiquitous when discussing air travel and severe weather. The jet stream is responsible for pushing highs and lows across the world and the mark the borders between colder and warmer air masses.

Jet streams are narrow bands of fast-moving wind in the high up in the atmosphere. Winds inside of a jet stream and range from 120 to 150 mph with the strongest winds in the very center. They are hundreds of miles across, several miles deep and thousands of miles long. A jet stream typically has a squiggly pattern since it follows troughs and ridges (areas of low and high pressure respectively). The winds inside jet streams consistently blow from west to east around the globe but this flow of air can easily wobble north and south. The reason for the west to east flow? The earth’s rotation.

If the earth didn’t rotate, air would just flow from the equator to the poles and back again. The rotation of the earth basically shoves the wind to the right thanks to the Coriolis Effect. How quickly the air flows in certain parts of the planet is dependent on the location. The equator is moving at a much faster speed than locations further north or south. The air ends up moving faster the more it moves away from the equator.

There are three atmospheric circulations: the Polar Cell, the Ferrel Cell and the Hadley Cell. They are located where temperatures changes are the greatest (in areas near 30°N and 50° to 60° N). The greater the temperature difference, the stronger the winds. The polar jet is located near 50° to 60°N (basically over Canada and sometimes the northern United States) and the subtropical jet is located at 30°N (over the southern United States).

The polar jet separates the frigid air from the North Pole from the warmer air further south. The mid-latitude air and much warmer equatorial air are separated by the subtropical jet. Most often you can find a jet stream right above and parallel to a strong cold front.

The jets shift to the north and south throughout the year because of changes in temperatures throughout the year. As colder air takes over during the winter, the polar jet shifts to the south and becomes stronger. The extra strength comes from the fact that the polar region gets colder during this time and the equator’s temperature remains the same.

The subtropical jet is felt the most during the winter over the southeastern US when there is an El Nino in the eastern Pacific. During El Nino years, those in southern Georgia and Florida actually experience colder and wetter conditions.

Science Behind the Forecast: Jet Stream

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