German Forces Enjoyed Early Success
The Germans were at an advantage in the early stages of the Battle. They took the Allies totally by surprise, and it took time for the American forces to gather themselves and mount a counteroffensive. In the meantime, continued bad weather and clever planning gave the Germans large inroads.
They managed to attack a weakly-defended area of the Allied line. This gave them reasonable levels of success early on, which led to enormous casualties and losses on the Allied side. However, the tide of the Battle gradually began to turn as time went on.