Many map apps have a small weather widget on the map to show the weather.

Creates.app

Google Maps

Apple Maps

OpenWeather offers 1,000 api calls for free. As the widget would need to request new data when the map is moved this is probably not enough.
Open Meteo is free for non commercial use. There up to 10.000 requests per day are ok, as far as I understand it they mean this 10.000 per device and not per application so that should be absolutely fine!