The organized look of your documentation makes me think that you can make it yourself if you learned some programming. Remember the ‘app’ does not have to work inside the sim, just the designed weather needs to be exported and then imported into the sim (XML).
Ofc. being able to edit/save/load inside the running sim would be nice, as i see it then making an external app that does as you describe is somewhat possible to make. With that said, then using online real data is not easy/cheap for a starter but is possible.
If i was to do it i would jump on UNITY and make it there. Unity is free and you are allowed to ‘sell’ your product, has good documentation and ‘easy’ cross-platform functionality.