If you're built to not rely on internet, an outdoor motion sensor with Luminance or Lux is your solve. I personally am comfortable with internet connectivity - I use OpenWeatherMap. You sort of get the best of all worlds here and it is astoundingly accurate. Note below - Local Sunrise (which is slightly more accurate than HE) and Illuminance and illuminated which give a numerical value for lux you can set as a comparator. I use this in a nice tile on my dashboards to have realtime weather as well as a source for running my LUX related rules - (see below)
A sample Lux related rule:
