Hmm, it's hard question
. I think, that weather is described by some varriable: How strong is the wind, the rain, the clouds are heavy. And if one of this is (for ex.) negative (maybe the wind speed is more than 10 m/s), global varriable "IsBadWeather" turning on. I have not studied the mechanism of action script weather, but maybe someday.....
.
PS. I'm sorry for my English - I'm from Poland, and I'm teaching English in school.