How can meteorologists use the jet stream to predict the weather

They used jet streams because they are formed by air masses which have temperature differences.  

The locations of the jet streams are also crucial for airplanes, because can generate turbulence, or vary the destination arrival time.

But meteorologists tend to follow and study this streams because they carry cyclones systems in lower atmosphere.

clumped distribution, because you'de have all of the population gathered in a relatively small are.

it's the most common because it provides protection and a mate for reproduction

example: humans, seeweed, cattles, etc.