My favorite by far is Weathergraph (widget image) Any 3rd party app that uses data from a weather service is going to have a subscription in order to pay for that weather data. Otherwise, your only real options are 1st party weather apps from the weather service companies themselves, like TWC, Accuweather, etc.
https://www.reddit.com/r/ios/comments/1d83i33/best_pay_once_weather_app/

