Here are two studies I made to experiment quick painting (don't laugh when I tell you the times)

The first one is in conditions closest to outdoor but form a photo on a table and in comfortable chair (about 1 hour)

The second one was more preprepared (I made a sketchy. Is that the correct word for a quick test?). I first did the sketch with a felt pen (20 min.) then paused and painted (1 hour)

No surprise the second sky is far better, at least closest to the original one. I regret that my river tilts to the left whereas in the first it is well horizontal. The second big error is the cliff which is too contrasted for a background. It is better in the first study where, as on the photo, the green tree is darker the the cliff. I totally missed that while painting.

So, there's good in either one, tell me if you see other things.