On 16 December 1944, at 5:30 am, the Germans began the attack with a 90-minute artillery attack using 1,600 artillery pieces. The Americans thought was that this was an attack resulting from the Allies' recent attack in the Wahlerscheid sector to the north. In the northern sector Dietrich's 6th Panzer Army was held up for almost 24 hours by a single platoon and four U.S. Forward Artillery Observers. They then attacked Losheim Gap and Elsenborn Ridge to get through to Liège and Antwerp. Heavy snowstorms occurred in the Ardennes area. This kept the Allied aircraft grounded, but it also slowed the German advance. There were massive traffic jams and fuel shortages. von Manteuffel's Fifth Panzer Army attacked towards Bastogne and St. Vith. In the south, Brandenberger's Seventh Army moved towards Luxembourg.