Both data sources are completely independent. yr.no refers to the Norwegian Meteorological Institute while OpenWeatherMap is a weather data service located in the U.S. Both have a worldwide coverage.
You can easily switch between both sources and decide, which provides the most accurate forecasts for your locations.
- yr.no has proven to be rather accurate in Europe. It provides a 7 day forecast, often with hourly forecasts for the first couple of days.
- OpenWeatherMap provides a 5 day forecast in 3 hour intervals.