Are you familiar with JSON passing from webservices? If not, it is a very worthwhile thing to take the time to learn.
The Weather Underground API site return JSON blobs from their services that contain the information you are looking for.
http://www.wunderground.com/weather/api/d/docs
Specifically, they give the details for the forecast here:
http://www.wunderground.com/weather/api/d/docs?d=data/forecast10day
and to get the current temp among many other things here:
http://www.wunderground.com/weather/api/d/docs?d=data/conditions