It sounds like a number of UK users have been posting in the SmartThings community that SmartWeather hasn’t been updating for them recently.
Another alternative is to use Media Tiles to display a weather forecast from a local news site or use an image from theweather.com/widget:
Widgets from theweather.com/widget have been popular since our release of background images and transparent tiles since you can set the background color of the image from theweather.com/widget to transparent.