Interesting. I just had to write one (non-UI5). Here is what you can do...
1. either use your browsers "geolocation" functionality (thought many folks turn it off or have it "ask" to know location.....or use a service like IPinfo.io (which I use) which will give you the info as JSON data.
2. use a weather service API.....openWeatherMap.org (OpenWeatherMap current weather and forecast) is an easy one with FREE use....though you have to register for a key.
3. if you want good weather icons, use Erik Flowers set (inspired by Font Awesome). Weather Icons - 222 font icons inspired by Font Awesome and designed for Bootstrap
So that will get you the data....then you can simply pull it into you UI5 interface as you like...easy peasy. 