Chimpware, this is probably not germain to the issue at hand, but it bears noting:
When I first researched how to obtain weather information from National Weather Service using their URL-based facilities, it quickly became clear that their data points were limited to very specific "stations" throughout the U.S.
See:
http://www.weather.gov/xml/current_obs/for a list of stations by state.
The "current conditions" weather report for each station shows a specific Latitude & Longitude pair, and I later found that trying to submit random lat/lon-based queries through NWS' feed services failed ... the lat/lon HAD to be in their database to work properly.
Is it possible that Google is using NWS as a back-end and therefore has similar constraints? I wonder if your plug-in might generate more reliable results if users were asked to first look up their nearest NWS-listed "weather station" lat/lon pair, and enter that instead of what Vera (or other source) tells them.
Again, just a thought...