You can use Metwit weather api simply passing latitude and longitude.
If you can implement them client-side: 200 request/day (ip based throttling) no authentication required. Worldwide coverage, JSON and REST compliant. You can register for extra API calls for free and if you still need it to call them server side the basic plan is pretty cheap.
Full disclosure: I own this API.
Take a look on this discussion. It seems relevant:
https://stackoverflow.com/questions/4876800/is-there-an-international-weather-forecast-api-that-is-not-limited-for-non-comme
Additionally type "weather forecast api" in google. There are tons of references to APIs that support several weather services.
Limit parameter is working fine:
select item.forecast from weather.forecast where woeid in
(select woeid from geo.places(1) where text="munic, de") and u='c' limit 3
and URL:
https://query.yahooapis.com/v1/public/yql?q=select%20item.forecast%20from%20weather.forecast%20where%20woeid%20in%20(select%20woeid%20from%20geo.places(1)%20where%20text%3D%22munic%2C%20de%22)%20and%20u%3D%27c%27%20limit%203&format=json
Update : It's not working anymore
It's much easier. Just add the parameter &d=5 to the string, like:
http://weather.yahooapis.com/forecastjson?w=24549429&u=c&d=5
if you want 5 days. Change json to rss for the RSS version.