are you saying the main "wcat" page is an HTML page and not an "app"
Two part question, two part answer:
1. "wcat" is not an html page. That's the main reason that the developer would have to make changes in what it displays.
2. "wcat" page is created and displayed by the app called WeatherCat. Which is why what is displayed is controlled by the developer.
The image you displayed in your first post is what you get with the "WeatherCat Controller" item in the WC->Tools menu. That is, again, created by the WC software and is controlled purely by the developer.
What I am referring to is a plain text file that you can create yourself with any Text editor Apple gives you one called "TextEdit" that should be in your Applications folder. Simply changing the file name's suffix from ".txt" to ".html" will automagically make it usable by a browser!
You simply use the appropriate WC "tags" listed in the Manual (Appendix 4) and a minimal amount of html tags. I suggested making a 'table' as that would be about the simplest way to display the data without any kind of 'formatting' needed.
You can then display the html file with any browser. The html file can be on your hard drive, just like any of your other files. You can actually open it by simply double-clicking it (assuming you changed the ".txt" to ".html" (or even ".htm").
If you can type, even with only two fingers, you can create a web page.