Hi Andy,
Yep, this sort of information is freely available from numerous sources with varying degrees of accuracy. In the UK, the met office produce a form called F214. Other companies produce other maps, here's a link to one by Jeppesen
JetPlan.com Graphic Weather: Winds and Temp
Fuel planning can be quite critical, particularly in large aircraft where it can make the difference of many thousands of $ whether you've got a 100kt head wind or tail wind. Too much fuel and it needs extra fuel burn just to carry the extra weight. Too little fuel and you can't get there.
Companies operating large aircraft have flight planning departments. A large part of their job is fuel planning.
Hope that helps.