Only in the Ubuntu channel, so haven't heard anything about jolla weather, but can assume that'll be the same. Seems a bit silly when we're just a conduit for the weather to get to the same watch, doesn't it ;)
From Jolla Weather we do not really need API key or whatever, just ability to peek at the data it managed to collect and shows on the phone.
Also I found Yahoo actually uses TWC as a provider, so effectively Yahoo Weather is a proxy to TWC. Of course it has different data format caching and update frequency, but still should provide comparable results.
Currently (re)searching which API provider would be best to use