As the seasons of colder weather begin in Southeastern Wisconsin, many weather reports will begin to place more emphasis on the Jet Stream. Jet streams are like rivers of wind high above in the atmosphere. These slim strips of strong winds have a huge influence on climate, as they can push air masses around and affect weather patterns.
The jet streams typically run from west to east, and their width is relatively narrow compared to their length. Jet streams are typically active at about 7 miles (11 kilometers) above the Earth’s surface and travel near the altitude of the tropopause, the transition between the troposphere and the stratosphere.
Jet streams are caused by a combination of a planet’s rotation on its axis and atmospheric heating by solar radiation. Jet streams form near boundaries of adjacent air masses with significant differences in temperature, such as the polar region and the warmer air towards the equator. Because air temperature influences jet streams, they are more active in the winter when there are wider ranges of temperatures between the competing Arctic and tropic air masses.
The actual appearance of jet streams result from the complex interaction between many variables – such as the location of high and low pressure systems, warm and cold air, and seasonal changes. They meander around the globe, dipping and rising in altitude/latitude, splitting at times and forming eddies, and even disappearing altogether to appear somewhere else.
Jet streams also “follow the sun” in that as the sun’s elevation increases each day in the spring, the average latitude of the jet stream shifts poleward. (By Summer in the Northern Hemisphere, it is typically found near the U.S. Canadian border.) As Autumn approaches and the sun’s elevation decreases, the jet stream’s average latitude moves toward the equator.
Also, the jet stream is often indicated by a line on maps and by television meteorologist. The line generally points to the location of the strongest wind. Jet streams are typically wider and not as distinct but a region where the wind increase toward a core of strongest wind.
One way of visualizing this is to consider a river. The river’s current is generally the strongest in the center with decreasing strength as one approaches the river’s bank. It can be said that jet streams are “rivers of air”.
Weather forecasters have an interest in the jet streams because they play an important role in determining the weather as they usually separate colder air and warmer air. Jet streams are one of the forces that push air masses around, moving weather systems to new areas. Jet streams don’t usually follow a straight path — they travel in patterns called peaks and troughs and they shift. Predicting these shifts is a major challenge for meteorologists.
USA Jet Stream Forecast Maps for Next 3-Days
Click on any image to enlarge it. Jet stream forecasts are courtesy of the University Corporation of Atmospheric Research (UCAR).