On my last jump from 10k, 3 of us went through a thick cloud layer at around 4500. (Used GPS for spot). Once in the cloud layer, there was no visibility and I had no clue where the other jumpers were. Then my Dytter went off at 3500 and I was still in the thick cloud with no visibility. That was pretty scary, since I told everyone I'm dumping at 3000. How low was this cloud layer going to go? Should I dump at 3000 regardless? Also, I didn't know where the other 2 jumpers were when we entered the cloud layer. Above or Below me? Maybe they are right above me and just don't know it. Finally visibility again just below 3000 and just before I go for my PC I see one of the jumpers doing a full track, but not away from me, more like to the side without really gaining too much distance. So he probably didn't know were I was either.
Anyways, the jump went well. My opinion, if you can avoid jumps over thick cloud layers, then do. But if you ever happen to be on a jump like this. Make good visual of all other jumpers before entering the clouds, so you know where to track. If you don't know where they are, don't track, because you don't where you're going.
Take Air.