The developer API has been shutdown and it is not possible to query for "common" data. But as a Personal Weather Station Contributor (login account) you can use the API's to query the WU for all PWS data present.
This is a different API call and well documented
docs.google.com/document/d/1eKCnKXI9xnoM...rOet08qpE_gArAY/edit
With the personalized API call you can query for data from a PWS and get the result in JSON or XLM format
Perhaps it is an better option to change from WU to Dark Sky Net where free API calls (1000 per day after login) can be made to query for the current weather and predictions. Same idea but from a different weather party.
Documentation
darksky.net/dev/docs
Example of a API query :
api.darksky.net/forecast/
[key]/[latitude],[longitude],[time]
Seems a good replacement of the WU right?