https://www.weather.gov/ is free (paid for via tax dollars) and has a lot of useful information. The map of the US with all the alerts and warnings on it is rather useful.

Are you suggesting there's no extra effort involved in taking a raw data feed and presenting it in an actually usable app for user?

I can get free weather details with the built-in iOS app, but I still bought Dark Sky because it's a better interface. I have no qualms with this purchase.

In Canada, the federal government has released their own weather app (WeatherCAN), including alerts for significant weather in your area. It's basically replaced the commercial weather apps on my phones.

I would pay for DarkSky if it was available here though; I quite appreciate their approach to location privacy: https://blog.darksky.net/location-privacy/