Regarding weather effect related problems (no solution as of yet):
As DrSuperGood hinted at, the Engine Heroes runs on handles everything in one thread (except: D3D11 calls (1 thread), voice (2 threads) and watchdog threads (80 to 101)). Meaning a slightly delayed packet (= data going over the internet), or a busy harddrive, or a busy PCIe-bus will stall the game causing an FPS drop (= stutter).