Different weather data sources will always be different, and may be different or similar but certain not exactly the same across all data sources every day. It's not a matter of Apple fixing it; it's just a different data source than what you're comparing it with. And of course, location is a factor too.
The sources used by Apple's weather app are described in this article, a link to which is also in the Weather app. You also have the option to report an issue and your local conditions to help improve the app. Sounds like that's something you could contribute to.
Learn more about regional availability and data sources for features in the Weather app.
support.apple.com