According to the Yahoo! Weather API documentation, a WOEID must be provided to obtain weather information for a specific region. The WOEID can be obtained by using the Yahoo! GeoPlanet service.
If I have a zip code, this is two API calls to obtain weather information.
Get the WOEID from a zip code: http://where.yahooapis.com/v1/places.q(19146)?appid=...
Get the weather info using WOEID: http://weather.yahooapis.com/forecastrss?w=12765532
However, after some web crawling I found that you can do the exact same thing with one API call:
http://xml.weather.yahoo.com/forecastrss?p=19146
I couldn't find any documentation on this. Is it safe to use in a production application?