Bug/Issue Big lag on weather or for no reason

First, i want to clarify a thing, i'm french and post my problem here because i have searching 1 hours for no result so I apologize for spelling errors.

Any way, my problem is that when the game raining, snowing and all weather OR sometimes in NO resaon^^ my game goes from 30 FPS to 10 FPS and i got a configuration greater than that requested for playing starbound. (processor 3,5 GHz and 12GB RAM, Ask me for more information about it ^^)And as I said above, with 1 hours of searching i got just 1 result does not work at me (Lol) and we can read the "Solution" at this link:

https://www.reddit.com/r/starbound/comments/1s8hf4/psa_eliminate_lag_on_pcs_that_normally_wouldnt/

and this:

http://www.edugeek.net/forums/gaming/39417-fix-steam-thinks-its-running-compatibility-mode.html

this is the same on both^^ then I went to see to find the entry "Steam.exe" and it does not appear to me :/
So I desperately seeks a solution here^^ Just to be clear, i can make run fallout 4 in normal quality with 60 FPS, so i think 30 FPS is not normal^^
Thank for reading me and waiting for a solution, have good day