The sensible thing to do would be to white list GOOD weather types.
e.g. Clear, Cloudy, Light Rain, Rain, Thunderstorm etc
Then, for edge weather types that you don't like, recategorise them.
e.g. Sandstorm becomes Thunderstorm, Mist becomes Light Rain, Fog becomes Rain, Snow becomes Thunderstorm etc
Then for other weather types, which you have no idea about because they're so infrequent you haven't encountered them, just use Cloudy.
What you may also choose to do is clip temperatures to 1c +/- 5c ? Assuming you go for 5c as the clip point:
e.g. -18c, Solar Storm Apocalypse becomes 5c, Cloudy .
e.g. -12, Snow becomes 5c, Thunderstorm.
Oh yes, and then there is 'Unknown' - Use the last weather value that you pulled down from Google ? e.g. It was Raining, then you get Unknown or have API issues or whatever causes that to happen, just fall back on the last good values you had.
I KNOW, it's really cool that you can have a Sandstorm in Bahrain, but really we'd love a bit of consistency and less fantastical weather. At the moment there is a bank of knowledge of iGP weather quirks that one has to acquire to make the correct choices, for example, Unknown weather is a Soft + Soft one stopper.
I've also made a lot of assumptions about what you can achieve by the current ways you're using the Google Weather API.
