I guess that must have been the reason why the nazis wouldn't dare launch an attack without unfavourable weather conditions for allied planes.
Nope, there are a plenty of reasons why the Nazis didn´t launch an attack earlier than the "Battle of the Bulge". Just think about the allied designated target of Operation "Market Garden" on the other side: Capturing intact bridges over the river rhine but also capturing enough deep water harbours supplying the troops and ending the "Red Ball Express" from normandy. Analysing history is not just saying "Ohh, that´s the best tank in WWII" or "Yeah, the nazis had the best armies in the fourties!"
Edit: Nor it is memorization of facts everybody does in history courses at school.