From what i've read the temperature contrasts between the subtropical and polar air mass along with the corriolis force create a strong wind high up in the atmosphere.  What I want to know is why the jet stream migrates northwards and southwards with the seasons and meanders around a bit?

First: streams are caused by pressure differences, not by "temperature contrasts".

So, when reasoning about such questiones, You always have to relate

how temperature gradients (vertical and horizontal) create pressure gradients.

Second: I am not familiar with the jet streams, but I know how the global circulation

works: The thermal equator "follows the sun".  In summer, the sun is in

zenith on the tropic of cancer, thus the factual band of zenithal rain shifts to the north.

(Same to the south in winter)

In short, the circulation zones (tropic = passat, ross latitudes, polar etc) are shifted north and  south following the sun. The jet streams, being part of that system, will

be shifted accordingly. Look here:

http://en.wikipedia.org/wiki/File:Jetcrosssection.jpg

Georg

the rocky mountains act as a barrier forcing the winds hitting them upwards the jet stream goes around this if it goes south low pressure systems form in the carribean causing hurricanes there and a wet summer in europe if it goes north the europeon high will dominate giving clear dry summers, global warming will not change the jet strem as it is purely coriolis force but the effect it has may change