Another thought...
I've been playing with software called SportTracks (see my thread about it here:
http://ecomodder.com/forum/showthrea...orts-8103.html). There is a "plugin" which will capture details about the weather from a specific wunderground.com station throughout your GPS track, so that you can map against your trip. Unfortunately, it pulls only from a specific station, so if your trip is longer, the information may not be so relevant.