There is a weather setup bug in the sessions settings... (this explains why I thought lighting under overcast is incorrect)... First thing I notice is that this option behaves different than previous versions. Now the weather options are linked between all sessions... i.e. If you set sunny for Practice, overcast for Qualifying and rain for Race.... what is happening is all three sessions are set the same rain.. or to which every you setup last.
If you select a weather preset: sunny, rain, etc. That is for all sessions. To set weather individual per session: Change the 4 weather icons 1 by 1. The weather preset will change to “scripted”.