Ralof mentions that Ulfric and the other Stormcloaks were ambushed at Darkwater Crossing "Like they knew exactly where we'd be" when we're sitting there talking with Gerdur.
My epiphany is, how did the Imperials know the Stormcloaks would be there? I am hoping there is some sort of quest, and in that quest you figure out if there is a traitor or spy among the Stormcloaks. So far I've traveled to Darkwater Crossing and turned up nothing in regards on how the Imperials knew where Ulfric would be.
Does any know if there is a quest involved or at least some clue as to how the Imperials knew where Ulfric would be?

!. Anyway, I'm going to go root around in both Windhelm and Solitude castles and see if I can't find something about how Ulfric got nailed. I'm willing to bet if its anywhere, its in the General's quarters. He would have had to order the ambush.