I am currently working on this.
My plan is to use a local weather station, that actually measures temp, humidity and radiation. Here is a picture:
Inside the Stevenson screen there is an arduino that transmit data to my rPi via a rfm12b module. (rfm2pi)
The data is archieved by emoncms in a mysql database, so it is accesible and could be used for this purpose
Tomorrow I will post all the info in my blog ( http://unpuntilloalambre.blogspot.com )
PS. Yes, I would write it in english 😉
Edit: Here is the blog post: