A: The jet stream is a high-altitude river of fast-moving air with wind speeds of 57 mph or greater. The two main jet streams that influence the USA's weather are the polar jet and the subtropical jet stream.A front is a boundary between different air masses.he jet stream forms along the polar front and it is the position of the polar front that determines where the jet stream is located. If the jet stream dives south in a meridional flow pattern, a cold dome of high pressure is allowed to slide into the USA and put the country in a deep freeze.