In FSX I just used real world weather. Although it wasn't always accurate. It did the job for me.

Now I'm looking for a free weather engine for P3D. I see al lot of them... I hope you can advise me what is the best one at the moment?

Thanks!

Don't know much about freeware weather engine (I'm an Hifisim Active Sky) customer, nevertheless when I lazy to start my second PC which host Active Sky 2016, I fire-up the free FSXWX : http://www.plane-pics.de/fsxwx/home.htm

Here are some shot I made month ago, trying to compare same situation with the two weather engine (FSxWX and Active Sky 2016.

FsxWX and below AS16 around Luchon, in south west of France :

 

Close to Luchon town, weather data known by FSxWX :

 

Same place, same moment, but with Active Sky 2016 :

Close to Brest (LFRB, west of France), 12'000 ft looking south :

 

FSxWX for Brest :

 

Active Sky for Brest :

 

Thanks for your detailed answer! 

Looks like AS16 is much better. 

What about OPUS? It's like AS16 and Ezdok in one right? I'm also looking for some ezdok effects so maybe Opus is a great solution?