Windy is fabulous!
Past data would be really nice to have feature, if it is not going to cost you., As understood from above discussion.
https://earth.nullschool.net help to view past data though am not sure if the website pays for it or some sponsors, it seems to fetch data on demand instead of storing.
If such an approach viable, your website could become a one place reference.
Thanks for providing a great experience with windy.