Not working anymore!
I know it is late and already had an accepted answer. But I will leave my thought just to benefit whoever came to here in search for more info.
Yahoo weather api has another format JSON.
http://weather.yahooapis.com/forecastjson?w=2459115&d=1
This API is undocumented but it will be useful for those who needs more forecasts. Adding parameter "d" will include more forecasts to returned data. I tried with different value for parameter "d". Unfortunately, it will only return forecasts for 4 more days regardless of different values I put in (1,2,3,4,5,a,c,d,...) .However, I believe this should be good enough for most cases.
**Note.. It is not working for rss though.