Sorry for the delay however I am looking into this now and noticed if you provide a valid key the Weather Underground request should work fine. Can you please verify you are getting the correct data by replacing the API_KEY and LOCATION in the URL below:
http://api.wunderground.com/api/API_KEY/yesterday/conditions/astronomy/q/LOCATION.json
That is the URL the weather service makes. My API key does still work correctly and returns the correct scale.
—
In regard to the OpenWeatherMaps returning invalid scales at night might be a known problem which we are working to resolve. I believe the system is using the incorrect forecast data for the next day.