If an object is moving at a constant velocity, it means that?

It will not change speed or direction when it is at a constant velocity. it will be a straight line graph.

Jet streams are relatively narrow bands of strong wind in the upper levels of the atmosphere. the winds blow from west to east in jet streams but the flow often shifts to the north and south. jet streams follow the boundaries between hot and cold air. the earth's rotation is responsible for the jet stream as well.