The Jet Stream is a relatively narrow band of strong winds in the upper levels of the atmosphere, in the northern hemisphere they blow from east to west, however it can shift to the north and south at times… Jet streams typically follow boundaries between warm and cold air and this is what will help bring mild or cold air to the northeast depending on the season. Remember air masses, jet streams divide and separate air masses.
Because they follow boundaries of temperature differences they are typically more pronounced in the winter months.
As the difference in temperature increases between two locations the strength of the winds in the jet stream tend to increase, these winds tend to be strongest in the upper levels of the atmosphere, however sometimes they can make it down to just above the surface which would be considered a low level jet, a topic for a different discussion.
Jet streams also follow the sun, as the angle of the sun increases in the spring months the latitude of where the jet stream sets up will typically migrate northward. As fall approaches and the angle of the sun becomes lower the jet streams will typically begin to migrate south once again.
One way to visualize the jet stream is to think about a river, the current is typically strongest in the middle of the river and that strength will usually decrease as you get closer to the riverbank. This is true with jet streams as well, the strongest winds will be noticed in the middle, however, the strength will decrease as you move further from the middle, jet streams can be seen as “rivers of air”.
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