The jetstream varies based on Coriolis effect, surface friction and tropopause. From day-to-day it changes and our flight plan is fully automated to make sure that we receive the maximum benefit of the wind. While avoiding bad weather of course!
At what flight level do you start to get really fast jet stream winds? 180 knots seems incredible. Is the jet stream faster over the ocean?It can vary but polar jet streams are usually in the 20-40M foot altitudes, and the subtropic jet streams tend to be between 30M and 50M feet. So with most flights staying around 35M feet, they try to hit those when possible to improve fuel consumption.
You can use this site:
http://weather.uwyo.edu/upperair/sounding.html to find airspeed (as well as other data) at various altitudes at any particular ground station. Pretty neat stuff I discovered in one of my aerospace engineering classes! We actually took several days' worth of data, and used some fancy matlab/mathematica programs to build graphs of average airspeed at various altitudes over DFW. If I can find it I'll post you a picture of what we compiled, if you want?