Lord Marrowgar question

Our guild went for our first attempt at ICC10 yesterday, and even thought we got past it after a number of attempts, it was still pretty messy and chaotic, and I'd like to better understand the fight, and maybe help us make it smoother, my main question being how the bonestorm target selection works, just googling and reading different articles and guides online isn't helping much, because they all seem to have a different explanation(or theory) about how it actually works.
Is there anyone who has actual experience on it on warmane(specifically frostmourne) that can give me a definitive answer on how it actually works, even if it's something as simple as "it's random".
I just want to be sure once and for all so we can plan our approach accordingly.
Thanks in advance

if i recall correctly it should target the person that's furthest away from the boss. However it seems to be, like you said, a bit messy.

Generally what you what to do is keep 2 group position when bonestorm starts.
Position A) Melee/Tanks/Heals
Position B) Range dps
more than likely the first bone storm will go towards Ranged. all they do is move out of the fire towards Position A). not all the way, just to get clear of the fire and continue dps.
bonestorm will then go to Position A). same as the first. but now all melee's move out of the fire towards Position B), Ranged in the mean time walk back to their original position.
from there its just rinse and repeat until bonestorm phase is over.
This is what people mean when they say PingPong-ing the boss. have your 2 groups move 1 unit so you always know where bonestorm is going to go next. bonestorm itself doesnt do that much. its the Fires that kill people. just stay clear of those and it should be a smooth ride.

The easiest way to do the marrowgar encounter is for everyone that is Position A) to stand right underneath (but still behind) the boss.
this makes it very easy to AOE down any spikes if they land in melee range.

if I remember correctly on warmane it has been setted to be random (but prefering the ones in "ranged" position over the ones in "melee")

It should allways travel to the person furthest away, however on warmane the first charge is random, after that, it does travel to the furthest away person for the rest of the duration, you take more dmg from the bonestorm itself the close you are to the boss + the flames becomes harder to avoid aswell the close you are.

I recommend having prot paladin / holy paladin using divine sacrifise at 1 sec before it starts, have your group spread out a little when he begins casting bonestorm, eventually have druids tranquility or priests use divine hymn to help healing.