It is easy to confuse the words upwind (upstream) and downwind (downstream). Suppose you are driving from the West toward the East. From your current position on the road, West is upstream and East is downstream. In forecasting, reference to upstream and downstream is important when describing the wind flow associated with the jet stream or explaining the trajectory of air along a trough or ridge. A way to remember the difference between the terms is to remember the word downstairs. Both downwind and downstairs lead you to your destination.

In meteorology, a wind direction is the direction the wind is coming from. For example, a Northwest wind is a wind flowing from Northwest toward Southeast. Upwind is the direction the wind is coming from. If the wind is blowing from the Northwest (blowing toward the Southeast) then the upwind direction is toward the Northwest and the downwind direction is toward the Southeast. In other words, if a person is moving upwind then they are moving against the wind and if a person is moving downwind they are moving with the wind.

The entrance sector is the "upstream sector" and the exit sector is the "downstream sector". These terms are often used when flow is described through a vort lobe or a jet streak.