How do conditions in the united states change when the jet stream moves north?

Since the jet stream is typically a westerly flow of air encircling the globe, at least in the NW US and Western Canada, a westerly wind usually brings clear skies and in the summer, warm weather and a SE wind usually brings rain and strong winds and generally inclement weather. In winter, the westerly wind would bring clear and cold conditions. If a plane was flying east it could presumably fly faster if it was in the jet stream.